diff --git a/src/Anon.cc b/src/Anon.cc
index 4c54510217..41544ab8c8 100644
--- a/src/Anon.cc
+++ b/src/Anon.cc
@@ -12,7 +12,7 @@
 #include "Reporter.h"
 
 
-AnonymizeIPAddr* ip_anonymizer[NUM_ADDR_ANONYMIZATION_METHODS] = {0};
+AnonymizeIPAddr* ip_anonymizer[NUM_ADDR_ANONYMIZATION_METHODS] = {nullptr};
 
 static uint32_t rand32()
 	{
@@ -148,7 +148,7 @@ AnonymizeIPAddr_A50::~AnonymizeIPAddr_A50()
 
 void AnonymizeIPAddr_A50::init()
 	{
-	root = next_free_node = 0;
+	root = next_free_node = nullptr;
 
 	// Prepare special nodes for 0.0.0.0 and 255.255.255.255.
 	memset(&special_nodes[0], 0, sizeof(special_nodes));
@@ -222,7 +222,7 @@ AnonymizeIPAddr_A50::Node* AnonymizeIPAddr_A50::new_node_block()
 	for ( int i = 1; i < block_size - 1; ++i )
 		block[i].child[0] = &block[i+1];
 
-	block[block_size - 1].child[0] = 0;
+	block[block_size - 1].child[0] = nullptr;
 	next_free_node = &block[1];
 
 	return &block[0];
@@ -276,12 +276,12 @@ AnonymizeIPAddr_A50::Node* AnonymizeIPAddr_A50::make_peer(ipaddr32_t a, Node* n)
 	Node* down[2];
 
 	if ( ! (down[0] = new_node()) )
-		return 0;
+		return nullptr;
 
 	if ( ! (down[1] = new_node()) )
 		{
 		free_node(down[0]);
-		return 0;
+		return nullptr;
 		}
 
 	// swivel is first bit 'a' and 'old->input' differ.
@@ -292,7 +292,7 @@ AnonymizeIPAddr_A50::Node* AnonymizeIPAddr_A50::make_peer(ipaddr32_t a, Node* n)
 
 	down[bitvalue]->input = a;
 	down[bitvalue]->output = make_output(n->output, swivel);
-	down[bitvalue]->child[0] = down[bitvalue]->child[1] = 0;
+	down[bitvalue]->child[0] = down[bitvalue]->child[1] = nullptr;
 
 	*down[1 - bitvalue] = *n;	// copy orig node down one level
 
@@ -316,7 +316,7 @@ AnonymizeIPAddr_A50::Node* AnonymizeIPAddr_A50::find_node(ipaddr32_t a)
 		root = new_node();
 		root->input = a;
 		root->output = rand32();
-		root->child[0] = root->child[1] = 0;
+		root->child[0] = root->child[1] = nullptr;
 
 		return root;
 		}
@@ -351,12 +351,12 @@ AnonymizeIPAddr_A50::Node* AnonymizeIPAddr_A50::find_node(ipaddr32_t a)
 		}
 
 	reporter->InternalError("out of memory!");
-	return 0;
+	return nullptr;
 	}
 
 void init_ip_addr_anonymizers()
 	{
-	ip_anonymizer[KEEP_ORIG_ADDR] = 0;
+	ip_anonymizer[KEEP_ORIG_ADDR] = nullptr;
 	ip_anonymizer[SEQUENTIALLY_NUMBERED] = new AnonymizeIPAddr_Seq();
 	ip_anonymizer[RANDOM_MD5] = new AnonymizeIPAddr_RandomMD5();
 	ip_anonymizer[PREFIX_PRESERVING_A50] = new AnonymizeIPAddr_A50();
@@ -365,7 +365,7 @@ void init_ip_addr_anonymizers()
 
 ipaddr32_t anonymize_ip(ipaddr32_t ip, enum ip_addr_anonymization_class_t cl)
 	{
-	TableVal* preserve_addr = 0;
+	TableVal* preserve_addr = nullptr;
 	AddrVal addr(ip);
 
 	int method = -1;
diff --git a/src/Attr.cc b/src/Attr.cc
index ea735b67f0..bf39c7f9c9 100644
--- a/src/Attr.cc
+++ b/src/Attr.cc
@@ -197,7 +197,7 @@ void Attributes::AddAttrs(Attributes* a)
 Attr* Attributes::FindAttr(attr_tag t) const
 	{
 	if ( ! attrs )
-		return 0;
+		return nullptr;
 
 	for ( const auto& a : *attrs )
 		{
@@ -205,7 +205,7 @@ Attr* Attributes::FindAttr(attr_tag t) const
 			return a;
 		}
 
-	return 0;
+	return nullptr;
 	}
 
 void Attributes::RemoveAttr(attr_tag t)
diff --git a/src/Base64.cc b/src/Base64.cc
index 51d2b707ad..16e43d296c 100644
--- a/src/Base64.cc
+++ b/src/Base64.cc
@@ -55,7 +55,7 @@ int* Base64Converter::InitBase64Table(const string& alphabet)
 	if ( alphabet == default_alphabet && default_table_initialized )
 		return default_base64_table;
 
-	int* base64_table = 0;
+	int* base64_table = nullptr;
 
 	if ( alphabet == default_alphabet )
 		{
@@ -98,7 +98,7 @@ Base64Converter::Base64Converter(Connection* arg_conn, const string& arg_alphabe
 		alphabet = default_alphabet;
 		}
 
-	base64_table = 0;
+	base64_table = nullptr;
 	base64_group_next = 0;
 	base64_padding = base64_after_padding = 0;
 	errored = 0;
@@ -234,7 +234,7 @@ BroString* decode_base64(const BroString* s, const BroString* a, Connection* con
 		{
 		reporter->Error("base64 decoding alphabet is not 64 characters: %s",
 		                a->CheckString());
-		return 0;
+		return nullptr;
 		}
 
 	int buf_len = int((s->Len() + 3) / 4) * 3 + 1;
@@ -259,7 +259,7 @@ BroString* decode_base64(const BroString* s, const BroString* a, Connection* con
 
 err:
 	delete [] rbuf;
-	return 0;
+	return nullptr;
 	}
 
 BroString* encode_base64(const BroString* s, const BroString* a, Connection* conn)
@@ -268,10 +268,10 @@ BroString* encode_base64(const BroString* s, const BroString* a, Connection* con
 		{
 		reporter->Error("base64 alphabet is not 64 characters: %s",
 		                a->CheckString());
-		return 0;
+		return nullptr;
 		}
 
-	char* outbuf = 0;
+	char* outbuf = nullptr;
 	int outlen = 0;
 	Base64Converter enc(conn, a ? a->CheckString() : "");
 	enc.Encode(s->Len(), (const unsigned char*) s->Bytes(), &outlen, &outbuf);
diff --git a/src/Base64.h b/src/Base64.h
index cdebc93017..2348eccc11 100644
--- a/src/Base64.h
+++ b/src/Base64.h
@@ -59,5 +59,5 @@ protected:
 
 };
 
-BroString* decode_base64(const BroString* s, const BroString* a = 0, Connection* conn = 0);
-BroString* encode_base64(const BroString* s, const BroString* a = 0, Connection* conn = 0);
+BroString* decode_base64(const BroString* s, const BroString* a = nullptr, Connection* conn = nullptr);
+BroString* encode_base64(const BroString* s, const BroString* a = nullptr, Connection* conn = nullptr);
diff --git a/src/BroString.cc b/src/BroString.cc
index 33a14a315b..cfd7e92c15 100644
--- a/src/BroString.cc
+++ b/src/BroString.cc
@@ -284,7 +284,7 @@ BroString* BroString::GetSubstring(int start, int len) const
 	{
 	// This code used to live in zeek.bif's sub_bytes() routine.
 	if ( start < 0 || start > n )
-		return 0;
+		return nullptr;
 
 	if ( len < 0 || len > n - start )
 		len = n - start;
@@ -302,7 +302,7 @@ BroString::Vec* BroString::Split(const BroString::IdxVec& indices) const
 	unsigned int i;
 
 	if ( indices.empty() )
-		return 0;
+		return nullptr;
 
 	// Copy input, ensuring space for "0":
 	IdxVec idx(1 + indices.size());
@@ -343,7 +343,7 @@ VectorVal* BroString:: VecToPolicy(Vec* vec)
 	VectorVal* result =
 		new VectorVal(internal_type("string_vec")->AsVectorType());
 	if ( ! result )
-		return 0;
+		return nullptr;
 
 	for ( unsigned int i = 0; i < vec->size(); ++i )
 		{
diff --git a/src/BroString.h b/src/BroString.h
index 40a1029291..66c3bce4b7 100644
--- a/src/BroString.h
+++ b/src/BroString.h
@@ -94,7 +94,7 @@ public:
 	//
 	// Note that you need to delete[] the resulting string.
 	//
-	char* Render(int format = EXPANDED_STRING, int* len = 0) const;
+	char* Render(int format = EXPANDED_STRING, int* len = nullptr) const;
 
 	// Similar to the above, but useful for output streams.
 	// Also more useful for debugging purposes since no deallocation
diff --git a/src/Brofiler.cc b/src/Brofiler.cc
index c406182747..a2391145cd 100644
--- a/src/Brofiler.cc
+++ b/src/Brofiler.cc
@@ -76,7 +76,7 @@ bool Brofiler::ReadStats()
 
 		pair<string, string> location_desc(std::move(location), std::move(desc));
 		uint64_t count;
-		atoi_n(cnt.size(), cnt.c_str(), 0, 10, count);
+		atoi_n(cnt.size(), cnt.c_str(), nullptr, 10, count);
 		usage_map.emplace(std::move(location_desc), count);
 		}
 
diff --git a/src/CompHash.cc b/src/CompHash.cc
index b28c9e307b..7d9a29da62 100644
--- a/src/CompHash.cc
+++ b/src/CompHash.cc
@@ -47,19 +47,19 @@ CompositeHash::CompositeHash(IntrusivePtr<TypeList> composite_type)
 		// via the singleton later.
 		singleton_tag = (*type->Types())[0]->InternalType();
 		size = 0;
-		key = 0;
+		key = nullptr;
 		}
 
 	else
 		{
-		size = ComputeKeySize(0, true, true);
+		size = ComputeKeySize(nullptr, true, true);
 
 		if ( size > 0 )
 			// Fixed size.  Make sure what we get is fully aligned.
 			key = reinterpret_cast<char*>
 				(new double[size/sizeof(double) + 1]);
 		else
-			key = 0;
+			key = nullptr;
 		}
 	}
 
@@ -72,7 +72,7 @@ CompositeHash::~CompositeHash()
 char* CompositeHash::SingleValHash(bool type_check, char* kp0,
 				   BroType* bt, Val* v, bool optional) const
 	{
-	char* kp1 = 0;
+	char* kp1 = nullptr;
 	InternalTypeTag t = bt->InternalType();
 
 	if ( optional )
@@ -90,7 +90,7 @@ char* CompositeHash::SingleValHash(bool type_check, char* kp0,
 		{
 		InternalTypeTag vt = v->Type()->InternalType();
 		if ( vt != t )
-			return 0;
+			return nullptr;
 		}
 
 	switch ( t ) {
@@ -186,12 +186,12 @@ char* CompositeHash::SingleValHash(bool type_check, char* kp0,
 				bool optional = (a && a->FindAttr(ATTR_OPTIONAL));
 
 				if ( ! (rv_i || optional) )
-					return 0;
+					return nullptr;
 
 				if ( ! (kp = SingleValHash(type_check, kp,
 							   rt->FieldType(i),
 							   rv_i, optional)) )
-					return 0;
+					return nullptr;
 				}
 
 			kp1 = kp;
@@ -242,7 +242,7 @@ char* CompositeHash::SingleValHash(bool type_check, char* kp0,
 
 				if ( ! (kp1 = SingleValHash(type_check, kp1, key->Type(), key,
 				                            false)) )
-					return 0;
+					return nullptr;
 
 				if ( ! v->Type()->IsSet() )
 					{
@@ -250,7 +250,7 @@ char* CompositeHash::SingleValHash(bool type_check, char* kp0,
 
 					if ( ! (kp1 = SingleValHash(type_check, kp1, val->Type(),
 								    val.get(), false)) )
-						return 0;
+						return nullptr;
 					}
 				}
 
@@ -278,7 +278,7 @@ char* CompositeHash::SingleValHash(bool type_check, char* kp0,
 					{
 					if ( ! (kp1 = SingleValHash(type_check, kp1,
 					                            vt->YieldType(), val, false)) )
-						return 0;
+						return nullptr;
 					}
 				}
 			}
@@ -295,7 +295,7 @@ char* CompositeHash::SingleValHash(bool type_check, char* kp0,
 				Val* v = lv->Index(i);
 				if ( ! (kp1 = SingleValHash(type_check, kp1, v->Type(), v,
 				                            false)) )
-					return 0;
+					return nullptr;
 				}
 			}
 			break;
@@ -303,7 +303,7 @@ char* CompositeHash::SingleValHash(bool type_check, char* kp0,
 		default:
 			{
 			reporter->InternalError("bad index type in CompositeHash::SingleValHash");
-			return 0;
+			return nullptr;
 			}
 		}
 
@@ -326,7 +326,7 @@ char* CompositeHash::SingleValHash(bool type_check, char* kp0,
 		break;
 
 	case TYPE_INTERNAL_ERROR:
-		return 0;
+		return nullptr;
 	}
 
 	return kp1;
@@ -361,7 +361,7 @@ HashKey* CompositeHash::ComputeHash(const Val* v, bool type_check) const
 		{
 		int sz = ComputeKeySize(v, type_check, false);
 		if ( sz == 0 )
-			return 0;
+			return nullptr;
 
 		k = reinterpret_cast<char*>(new double[sz/sizeof(double) + 1]);
 		type_check = false;	// no need to type-check again.
@@ -370,18 +370,18 @@ HashKey* CompositeHash::ComputeHash(const Val* v, bool type_check) const
 	const type_list* tl = type->Types();
 
 	if ( type_check && v->Type()->Tag() != TYPE_LIST )
-		return 0;
+		return nullptr;
 
 	const val_list* vl = v->AsListVal()->Vals();
 	if ( type_check && vl->length() != tl->length() )
-		return 0;
+		return nullptr;
 
 	char* kp = k;
 	loop_over_list(*tl, i)
 		{
 		kp = SingleValHash(type_check, kp, (*tl)[i], (*vl)[i], false);
 		if ( ! kp )
-			return 0;
+			return nullptr;
 		}
 
 	return new HashKey((k == key), (void*) k, kp - k);
@@ -393,13 +393,13 @@ HashKey* CompositeHash::ComputeSingletonHash(const Val* v, bool type_check) cons
 		{
 		const val_list* vl = v->AsListVal()->Vals();
 		if ( type_check && vl->length() != 1 )
-			return 0;
+			return nullptr;
 
 		v = (*vl)[0];
 		}
 
 	if ( type_check && v->Type()->InternalType() != singleton_tag )
-		return 0;
+		return nullptr;
 
 	switch ( singleton_tag ) {
 	case TYPE_INTERNAL_INT:
@@ -434,17 +434,17 @@ HashKey* CompositeHash::ComputeSingletonHash(const Val* v, bool type_check) cons
 			}
 
 		reporter->InternalError("bad index type in CompositeHash::ComputeSingletonHash");
-		return 0;
+		return nullptr;
 
 	case TYPE_INTERNAL_STRING:
 		return new HashKey(v->AsString());
 
 	case TYPE_INTERNAL_ERROR:
-		return 0;
+		return nullptr;
 
 	default:
 		reporter->InternalError("bad internal type in CompositeHash::ComputeSingletonHash");
-		return 0;
+		return nullptr;
 	}
 	}
 
@@ -507,7 +507,7 @@ int CompositeHash::SingleTypeKeySize(BroType* bt, const Val* v,
 
 		case TYPE_RECORD:
 			{
-			const RecordVal* rv = v ? v->AsRecordVal() : 0;
+			const RecordVal* rv = v ? v->AsRecordVal() : nullptr;
 			RecordType* rt = bt->AsRecordType();
 			int num_fields = rt->NumFields();
 
@@ -517,7 +517,7 @@ int CompositeHash::SingleTypeKeySize(BroType* bt, const Val* v,
 				bool optional = (a && a->FindAttr(ATTR_OPTIONAL));
 
 				sz = SingleTypeKeySize(rt->FieldType(i),
-						       rv ? rv->Lookup(i) : 0,
+						       rv ? rv->Lookup(i) : nullptr,
 						       type_check, sz, optional,
 						       calc_static_size);
 				if ( ! sz )
@@ -632,7 +632,7 @@ int CompositeHash::SingleTypeKeySize(BroType* bt, const Val* v,
 int CompositeHash::ComputeKeySize(const Val* v, bool type_check, bool calc_static_size) const
 	{
 	const type_list* tl = type->Types();
-	const val_list* vl = 0;
+	const val_list* vl = nullptr;
 	if ( v )
 		{
 		if ( type_check && v->Type()->Tag() != TYPE_LIST )
@@ -646,7 +646,7 @@ int CompositeHash::ComputeKeySize(const Val* v, bool type_check, bool calc_stati
 	int sz = 0;
 	loop_over_list(*tl, i)
 		{
-		sz = SingleTypeKeySize((*tl)[i], v ? v->AsListVal()->Index(i) : 0,
+		sz = SingleTypeKeySize((*tl)[i], v ? v->AsListVal()->Index(i) : nullptr,
 				       type_check, sz, false, calc_static_size);
 		if ( ! sz )
 			return 0;
@@ -745,7 +745,7 @@ const char* CompositeHash::RecoverOneVal(const HashKey* k, const char* kp0,
 
 	TypeTag tag = t->Tag();
 	InternalTypeTag it = t->InternalType();
-	const char* kp1 = 0;
+	const char* kp1 = nullptr;
 
 	if ( optional )
 		{
diff --git a/src/Conn.cc b/src/Conn.cc
index bc37dea87a..95ee5af8f2 100644
--- a/src/Conn.cc
+++ b/src/Conn.cc
@@ -120,7 +120,7 @@ Connection::Connection(NetSessions* s, const ConnIDKey& k, double t, const ConnI
 	if ( arg_encap )
 		encapsulation = new EncapsulationStack(*arg_encap);
 	else
-		encapsulation = 0;
+		encapsulation = nullptr;
 	}
 
 Connection::~Connection()
@@ -132,7 +132,7 @@ Connection::~Connection()
 
 	if ( conn_val )
 		{
-		conn_val->SetOrigin(0);
+		conn_val->SetOrigin(nullptr);
 		Unref(conn_val);
 		}
 
@@ -148,7 +148,7 @@ void Connection::CheckEncapsulation(const EncapsulationStack* arg_encap)
 		{
 		if ( *encapsulation != *arg_encap )
 			{
-			Event(tunnel_changed, 0, arg_encap->GetVectorVal());
+			Event(tunnel_changed, nullptr, arg_encap->GetVectorVal());
 			delete encapsulation;
 			encapsulation = new EncapsulationStack(*arg_encap);
 			}
@@ -157,14 +157,14 @@ void Connection::CheckEncapsulation(const EncapsulationStack* arg_encap)
 	else if ( encapsulation )
 		{
 		EncapsulationStack empty;
-		Event(tunnel_changed, 0, empty.GetVectorVal());
+		Event(tunnel_changed, nullptr, empty.GetVectorVal());
 		delete encapsulation;
 		encapsulation = nullptr;
 		}
 
 	else if ( arg_encap )
 		{
-		Event(tunnel_changed, 0, arg_encap->GetVectorVal());
+		Event(tunnel_changed, nullptr, arg_encap->GetVectorVal());
 		encapsulation = new EncapsulationStack(*arg_encap);
 		}
 	}
@@ -269,7 +269,7 @@ void Connection::HistoryThresholdEvent(EventHandlerPtr e, bool is_orig,
 void Connection::DeleteTimer(double /* t */)
 	{
 	if ( is_active )
-		Event(connection_timeout, 0);
+		Event(connection_timeout, nullptr);
 
 	sessions->Remove(this);
 	}
@@ -282,7 +282,7 @@ void Connection::InactivityTimer(double t)
 		{
 		if ( last_time + inactivity_timeout <= t )
 			{
-			Event(connection_timeout, 0);
+			Event(connection_timeout, nullptr);
 			sessions->Remove(this);
 			++killed_by_inactivity;
 			}
@@ -402,12 +402,12 @@ RecordVal* Connection::BuildConnVal()
 
 analyzer::Analyzer* Connection::FindAnalyzer(analyzer::ID id)
 	{
-	return root_analyzer ? root_analyzer->FindChild(id) : 0;
+	return root_analyzer ? root_analyzer->FindChild(id) : nullptr;
 	}
 
 analyzer::Analyzer* Connection::FindAnalyzer(const analyzer::Tag& tag)
 	{
-	return root_analyzer ? root_analyzer->FindChild(tag) : 0;
+	return root_analyzer ? root_analyzer->FindChild(tag) : nullptr;
 	}
 
 analyzer::Analyzer* Connection::FindAnalyzer(const char* name)
@@ -696,7 +696,7 @@ void Connection::CheckFlowLabel(bool is_orig, uint32_t flow_label)
 		if ( connection_flow_label_changed &&
 		     (is_orig ? saw_first_orig_packet : saw_first_resp_packet) )
 			{
-			EnqueueEvent(connection_flow_label_changed, 0,
+			EnqueueEvent(connection_flow_label_changed, nullptr,
 				IntrusivePtr{AdoptRef{}, BuildConnVal()},
 				IntrusivePtr{AdoptRef{}, val_mgr->GetBool(is_orig)},
 				IntrusivePtr{AdoptRef{}, val_mgr->GetCount(my_flow_label)},
diff --git a/src/Conn.h b/src/Conn.h
index a2bb1face5..5048a98f0f 100644
--- a/src/Conn.h
+++ b/src/Conn.h
@@ -180,13 +180,13 @@ public:
 	// given that event's first argument will be it, and it's second will be
 	// the connection value.  If 'name' is null, then the event's first
 	// argument is the connection value.
-	void Event(EventHandlerPtr f, analyzer::Analyzer* analyzer, const char* name = 0);
+	void Event(EventHandlerPtr f, analyzer::Analyzer* analyzer, const char* name = nullptr);
 
 	// If a handler exists for 'f', an event will be generated.  In any case,
 	// 'v1' and 'v2' reference counts get decremented.  The event's first
 	// argument is the connection value, second argument is 'v1', and if 'v2'
 	// is given that will be it's third argument.
-	void Event(EventHandlerPtr f, analyzer::Analyzer* analyzer, Val* v1, Val* v2 = 0);
+	void Event(EventHandlerPtr f, analyzer::Analyzer* analyzer, Val* v1, Val* v2 = nullptr);
 
 	// If a handler exists for 'f', an event will be generated.  In any case,
 	// reference count for each element in the 'vl' list are decremented.  The
diff --git a/src/DFA.cc b/src/DFA.cc
index e99e772fcc..071a8f9570 100644
--- a/src/DFA.cc
+++ b/src/DFA.cc
@@ -17,7 +17,7 @@ DFA_State::DFA_State(int arg_state_num, const EquivClass* ec,
 	num_sym = ec->NumClasses();
 	nfa_states = arg_nfa_states;
 	accept = arg_accept;
-	mark = 0;
+	mark = nullptr;
 
 	SymPartition(ec);
 
@@ -96,7 +96,7 @@ DFA_State* DFA_State::ComputeXtion(int sym, DFA_Machine* machine)
 	else
 		{
 		delete ns;
-		next_d = 0;	// Jam
+		next_d = nullptr;	// Jam
 		}
 
 	AddXtion(equiv_sym, next_d);
@@ -182,7 +182,7 @@ void DFA_State::ClearMarks()
 	{
 	if ( mark )
 		{
-		SetMark(0);
+		SetMark(nullptr);
 
 		for ( int i = 0; i < num_sym; ++i )
 			{
@@ -395,7 +395,7 @@ DFA_Machine::DFA_Machine(NFA_Machine* n, EquivClass* arg_ec)
 		}
 	else
 		{
-		start_state = 0; // Jam
+		start_state = nullptr; // Jam
 		delete ns;
 		}
 	}
@@ -451,7 +451,7 @@ bool DFA_Machine::StateSetToDFA_State(NFA_state_list* state_set,
 	if ( accept->empty() )
 		{
 		delete accept;
-		accept = 0;
+		accept = nullptr;
 		}
 
 	DFA_State* ds = new DFA_State(state_count++, ec, state_set, accept);
diff --git a/src/DNS_Mgr.cc b/src/DNS_Mgr.cc
index e0bc8ffe90..b39ba83aab 100644
--- a/src/DNS_Mgr.cc
+++ b/src/DNS_Mgr.cc
@@ -194,7 +194,7 @@ DNS_Mapping::DNS_Mapping(const IPAddr& addr, struct hostent* h, uint32_t ttl)
 	{
 	Init(h);
 	req_addr = addr;
-	req_host = 0;
+	req_host = nullptr;
 	req_ttl = ttl;
 	}
 
@@ -203,7 +203,7 @@ DNS_Mapping::DNS_Mapping(FILE* f)
 	Clear();
 	init_failed = true;
 
-	req_host = 0;
+	req_host = nullptr;
 	req_ttl = 0;
 	creation_time = 0;
 
@@ -255,7 +255,7 @@ DNS_Mapping::DNS_Mapping(FILE* f)
 			}
 		}
 	else
-		addrs = 0;
+		addrs = nullptr;
 
 	init_failed = false;
 	}
@@ -302,7 +302,7 @@ IntrusivePtr<TableVal> DNS_Mapping::AddrsSet() {
 IntrusivePtr<StringVal> DNS_Mapping::Host()
 	{
 	if ( failed || num_names == 0 || ! names[0] )
-		return 0;
+		return nullptr;
 
 	if ( ! host_val )
 		host_val = make_intrusive<StringVal>(names[0]);
@@ -315,8 +315,8 @@ void DNS_Mapping::Init(struct hostent* h)
 	no_mapping = false;
 	init_failed = false;
 	creation_time = current_time();
-	host_val = 0;
-	addrs_val = 0;
+	host_val = nullptr;
+	addrs_val = nullptr;
 
 	if ( ! h )
 		{
@@ -327,7 +327,7 @@ void DNS_Mapping::Init(struct hostent* h)
 	map_type = h->h_addrtype;
 	num_names = 1;	// for now, just use official name
 	names = new char*[num_names];
-	names[0] = h->h_name ? copy_string(h->h_name) : 0;
+	names[0] = h->h_name ? copy_string(h->h_name) : nullptr;
 
 	for ( num_addrs = 0; h->h_addr_list[num_addrs]; ++num_addrs )
 		;
@@ -344,7 +344,7 @@ void DNS_Mapping::Init(struct hostent* h)
 				                  IPAddr::Network);
 		}
 	else
-		addrs = 0;
+		addrs = nullptr;
 
 	failed = false;
 	}
@@ -352,10 +352,10 @@ void DNS_Mapping::Init(struct hostent* h)
 void DNS_Mapping::Clear()
 	{
 	num_names = num_addrs = 0;
-	names = 0;
-	addrs = 0;
-	host_val = 0;
-	addrs_val = 0;
+	names = nullptr;
+	addrs = nullptr;
+	host_val = nullptr;
+	addrs_val = nullptr;
 	no_mapping = false;
 	map_type = 0;
 	failed = true;
@@ -363,7 +363,7 @@ void DNS_Mapping::Clear()
 
 void DNS_Mapping::Save(FILE* f) const
 	{
-	fprintf(f, "%.0f %d %s %d %s %d %d %" PRIu32"\n", creation_time, req_host != 0,
+	fprintf(f, "%.0f %d %s %d %s %d %d %" PRIu32"\n", creation_time, req_host != nullptr,
 		req_host ? req_host : req_addr.AsString().c_str(),
 		failed, (names && names[0]) ? names[0] : "*",
 		map_type, num_addrs, req_ttl);
@@ -381,11 +381,11 @@ DNS_Mgr::DNS_Mgr(DNS_MgrMode arg_mode)
 
 	dns_mapping_valid = dns_mapping_unverified = dns_mapping_new_name =
 		dns_mapping_lost_name = dns_mapping_name_changed =
-			dns_mapping_altered =  0;
+			dns_mapping_altered =  nullptr;
 
-	dm_rec = 0;
+	dm_rec = nullptr;
 
-	cache_name = dir = 0;
+	cache_name = dir = nullptr;
 
 	asyncs_pending = 0;
 	num_requests = 0;
@@ -540,7 +540,7 @@ IntrusivePtr<TableVal> DNS_Mgr::LookupHost(const char* name)
 
 	case DNS_FORCE:
 		reporter->FatalError("can't find DNS entry for %s in cache", name);
-		return 0;
+		return nullptr;
 
 	case DNS_DEFAULT:
 		requests.push_back(new DNS_Mgr_Request(name, AF_INET, false));
@@ -550,7 +550,7 @@ IntrusivePtr<TableVal> DNS_Mgr::LookupHost(const char* name)
 
 	default:
 		reporter->InternalError("bad mode in DNS_Mgr::LookupHost");
-		return 0;
+		return nullptr;
 	}
 	}
 
@@ -585,7 +585,7 @@ IntrusivePtr<Val> DNS_Mgr::LookupAddr(const IPAddr& addr)
 	case DNS_FORCE:
 		reporter->FatalError("can't find DNS entry for %s in cache",
 		    addr.AsString().c_str());
-		return 0;
+		return nullptr;
 
 	case DNS_DEFAULT:
 		requests.push_back(new DNS_Mgr_Request(addr));
@@ -594,7 +594,7 @@ IntrusivePtr<Val> DNS_Mgr::LookupAddr(const IPAddr& addr)
 
 	default:
 		reporter->InternalError("bad mode in DNS_Mgr::LookupAddr");
-		return 0;
+		return nullptr;
 	}
 	}
 
@@ -634,7 +634,7 @@ void DNS_Mgr::Resolve()
 				DNS_Mgr_Request* dr = requests[i];
 				if ( dr->RequestPending() )
 					{
-					AddResult(dr, 0);
+					AddResult(dr, nullptr);
 					dr->RequestDone();
 					}
 				}
@@ -748,7 +748,7 @@ IntrusivePtr<Val> DNS_Mgr::BuildMappingVal(DNS_Mapping* dm)
 
 void DNS_Mgr::AddResult(DNS_Mgr_Request* dr, struct nb_dns_result* r)
 	{
-	struct hostent* h = (r && r->host_errno == 0) ? r->hostent : 0;
+	struct hostent* h = (r && r->host_errno == 0) ? r->hostent : nullptr;
 	u_int32_t ttl = (r && r->host_errno == 0) ? r->ttl : 0;
 
 	DNS_Mapping* new_dm;
@@ -758,7 +758,7 @@ void DNS_Mgr::AddResult(DNS_Mgr_Request* dr, struct nb_dns_result* r)
 	if ( dr->ReqHost() )
 		{
 		new_dm = new DNS_Mapping(dr->ReqHost(), h, ttl);
-		prev_dm = 0;
+		prev_dm = nullptr;
 
 		if ( dr->ReqIsTxt() )
 			{
@@ -784,10 +784,10 @@ void DNS_Mgr::AddResult(DNS_Mgr_Request* dr, struct nb_dns_result* r)
 			if ( it == host_mappings.end() )
 				{
 				host_mappings[dr->ReqHost()].first =
-					new_dm->Type() == AF_INET ? new_dm : 0;
+					new_dm->Type() == AF_INET ? new_dm : nullptr;
 
 				host_mappings[dr->ReqHost()].second =
-					new_dm->Type() == AF_INET ? 0 : new_dm;
+					new_dm->Type() == AF_INET ? nullptr : new_dm;
 				}
 			else
 				{
@@ -980,7 +980,7 @@ const char* DNS_Mgr::LookupAddrInCache(const IPAddr& addr)
 	AddrMap::iterator it = addr_mappings.find(addr);
 
 	if ( it == addr_mappings.end() )
-		return 0;
+		return nullptr;
 
 	DNS_Mapping* d = it->second;
 
@@ -988,7 +988,7 @@ const char* DNS_Mgr::LookupAddrInCache(const IPAddr& addr)
 		{
 		addr_mappings.erase(it);
 		delete d;
-		return 0;
+		return nullptr;
 		}
 
 	// The escapes in the following strings are to avoid having it
@@ -1002,21 +1002,21 @@ IntrusivePtr<TableVal> DNS_Mgr::LookupNameInCache(const string& name)
 	if ( it == host_mappings.end() )
 		{
 		it = host_mappings.begin();
-		return 0;
+		return nullptr;
 		}
 
 	DNS_Mapping* d4 = it->second.first;
 	DNS_Mapping* d6 = it->second.second;
 
 	if ( ! d4 || ! d4->names || ! d6 || ! d6->names )
-		return 0;
+		return nullptr;
 
 	if ( d4->Expired() || d6->Expired() )
 		{
 		host_mappings.erase(it);
 		delete d4;
 		delete d6;
-		return 0;
+		return nullptr;
 		}
 
 	auto tv4 = d4->AddrsSet();
@@ -1029,7 +1029,7 @@ const char* DNS_Mgr::LookupTextInCache(const string& name)
 	{
 	TextMap::iterator it = text_mappings.find(name);
 	if ( it == text_mappings.end() )
-		return 0;
+		return nullptr;
 
 	DNS_Mapping* d = it->second;
 
@@ -1037,7 +1037,7 @@ const char* DNS_Mgr::LookupTextInCache(const string& name)
 		{
 		text_mappings.erase(it);
 		delete d;
-		return 0;
+		return nullptr;
 		}
 
 	// The escapes in the following strings are to avoid having it
@@ -1077,7 +1077,7 @@ void DNS_Mgr::AsyncLookupAddr(const IPAddr& host, LookupCallback* callback)
 		return;
 		}
 
-	AsyncRequest* req = 0;
+	AsyncRequest* req = nullptr;
 
 	// Have we already a request waiting for this host?
 	AsyncRequestAddrMap::iterator i = asyncs_addrs.find(host);
@@ -1115,7 +1115,7 @@ void DNS_Mgr::AsyncLookupName(const string& name, LookupCallback* callback)
 		return;
 		}
 
-	AsyncRequest* req = 0;
+	AsyncRequest* req = nullptr;
 
 	// Have we already a request waiting for this host?
 	AsyncRequestNameMap::iterator i = asyncs_names.find(name);
@@ -1154,7 +1154,7 @@ void DNS_Mgr::AsyncLookupNameText(const string& name, LookupCallback* callback)
 		return;
 		}
 
-	AsyncRequest* req = 0;
+	AsyncRequest* req = nullptr;
 
 	// Have we already a request waiting for this host?
 	AsyncRequestTextMap::iterator i = asyncs_texts.find(name);
diff --git a/src/DbgBreakpoint.cc b/src/DbgBreakpoint.cc
index 7bd18ce05f..094b46a33e 100644
--- a/src/DbgBreakpoint.cc
+++ b/src/DbgBreakpoint.cc
@@ -49,13 +49,13 @@ DbgBreakpoint::DbgBreakpoint()
 	enabled = temporary = false;
 	BPID = -1;
 
-	at_stmt = 0;
+	at_stmt = nullptr;
 	at_time = -1.0;
 
 	repeat_count = hit_count = 0;
 
 	description[0] = 0;
-	source_filename = 0;
+	source_filename = nullptr;
 	source_line = 0;
 	}
 
diff --git a/src/Debug.cc b/src/Debug.cc
index 7bc6e3f4bb..3a13a4c7f7 100644
--- a/src/Debug.cc
+++ b/src/Debug.cc
@@ -55,7 +55,7 @@ DebuggerState::DebuggerState()
 	BreakFromSignal(false);
 
 	// ### Don't choose this arbitrary size! Extend Frame.
-	dbg_locals = new Frame(1024, /* func = */ 0, /* fn_args = */ 0);
+	dbg_locals = new Frame(1024, /* func = */ nullptr, /* fn_args = */ nullptr);
 	}
 
 DebuggerState::~DebuggerState()
@@ -107,7 +107,7 @@ FILE* TraceState::SetTraceFile(const char* filename)
 	else
 		{
 		fprintf(stderr, "Unable to open trace file %s\n", filename);
-		trace_file = 0;
+		trace_file = nullptr;
 		}
 
 	return oldfile;
@@ -137,7 +137,7 @@ int TraceState::LogTrace(const char* fmt, ...)
 
 	const Stmt* stmt;
 	Location loc;
-	loc.filename = 0;
+	loc.filename = nullptr;
 
 	if ( g_frame_stack.size() > 0 && g_frame_stack.back() )
 		{
@@ -178,7 +178,7 @@ void get_first_statement(Stmt* list, Stmt*& first, Location& loc)
 	{
 	if ( ! list )
 		{
-		first = 0;
+		first = nullptr;
 		return;
 		}
 
@@ -231,7 +231,7 @@ static void parse_function_name(vector<ParseLocationRec>& result,
 		return;
 		}
 
-	Stmt* body = 0;	// the particular body we care about; 0 = all
+	Stmt* body = nullptr;	// the particular body we care about; 0 = all
 
 	if ( bodies.size() == 1 )
 		body = bodies[0].stmts.get();
@@ -380,7 +380,7 @@ vector<ParseLocationRec> parse_location_string(const string& s)
 			return result;
 			}
 
-		StmtLocMapping* hit = 0;
+		StmtLocMapping* hit = nullptr;
 		for ( const auto entry : *(iter->second) )
 			{
 			plr.filename = entry->Loc().filename;
@@ -399,7 +399,7 @@ vector<ParseLocationRec> parse_location_string(const string& s)
 		if ( hit )
 			plr.stmt = hit->Statement();
 		else
-			plr.stmt = 0;
+			plr.stmt = nullptr;
 		}
 
 	return result;
@@ -730,7 +730,7 @@ static char* get_prompt(bool reset_counter = false)
 string get_context_description(const Stmt* stmt, const Frame* frame)
 	{
 	ODesc d;
-	const BroFunc* func = frame ? frame->GetFunction() : 0;
+	const BroFunc* func = frame ? frame->GetFunction() : nullptr;
 
 	if ( func )
 		func->DescribeDebug(&d, frame->GetFuncArgs());
@@ -758,7 +758,7 @@ string get_context_description(const Stmt* stmt, const Frame* frame)
 
 int dbg_handle_debug_input()
 	{
-	static char* input_line = 0;
+	static char* input_line = nullptr;
 	int status = 0;
 
 	if ( g_debugger_state.BreakFromSignal() )
@@ -820,7 +820,7 @@ int dbg_handle_debug_input()
 		if ( input_line )
 			{
 			free(input_line);	// this was malloc'ed
-			input_line = 0;
+			input_line = nullptr;
 			}
 		else
 			exit(0);
@@ -934,8 +934,8 @@ bool post_execute_stmt(Stmt* stmt, Frame* f, Val* result, stmt_flow_type* flow)
 
 // Evaluates the given expression in the context of the currently selected
 // frame.  Returns the resulting value, or nil if none (or there was an error).
-Expr* g_curr_debug_expr = 0;
-const char* g_curr_debug_error = 0;
+Expr* g_curr_debug_expr = nullptr;
+const char* g_curr_debug_error = nullptr;
 bool in_debug = false;
 
 // ### fix this hardwired access to external variables etc.
@@ -993,7 +993,7 @@ IntrusivePtr<Val> dbg_eval_expr(const char* expr)
 		if ( g_curr_debug_expr )
 			{
 			delete g_curr_debug_expr;
-			g_curr_debug_expr = 0;
+			g_curr_debug_expr = nullptr;
 			}
 		}
 	else
@@ -1003,9 +1003,9 @@ IntrusivePtr<Val> dbg_eval_expr(const char* expr)
 		pop_scope();
 
 	delete g_curr_debug_expr;
-	g_curr_debug_expr = 0;
+	g_curr_debug_expr = nullptr;
 	delete [] g_curr_debug_error;
-	g_curr_debug_error = 0;
+	g_curr_debug_error = nullptr;
 	in_debug = false;
 
 	return result;
diff --git a/src/Debug.h b/src/Debug.h
index 676c587635..bfbac98d70 100644
--- a/src/Debug.h
+++ b/src/Debug.h
@@ -149,7 +149,7 @@ bool post_execute_stmt(Stmt* stmt, Frame* f, Val* result, stmt_flow_type* flow);
 // Returns 1 if successful, 0 otherwise.
 // If cmdfile is non-nil, it contains the location of a file of commands
 // to be executed as debug commands.
-int dbg_init_debugger(const char* cmdfile = 0);
+int dbg_init_debugger(const char* cmdfile = nullptr);
 int dbg_shutdown_debugger();
 
 // Returns 1 if successful, 0 otherwise.
diff --git a/src/DebugCmds.cc b/src/DebugCmds.cc
index b65d979f5e..eb284a6c69 100644
--- a/src/DebugCmds.cc
+++ b/src/DebugCmds.cc
@@ -125,7 +125,7 @@ void choose_global_symbols_regex(const string& regex, vector<ID*>& choices,
 PQueue<DebugCmdInfo> g_DebugCmdInfos;
 
 DebugCmdInfo::DebugCmdInfo(const DebugCmdInfo& info)
-: cmd(info.cmd), helpstring(0)
+: cmd(info.cmd), helpstring(nullptr)
 	{
 	num_names = info.num_names;
 	names = info.names;
@@ -153,7 +153,7 @@ const DebugCmdInfo* get_debug_cmd_info(DebugCmd cmd)
 	if ( (int) cmd < g_DebugCmdInfos.length() )
 		return g_DebugCmdInfos[(int) cmd];
 	else
-		return 0;
+		return nullptr;
 	}
 
 int find_all_matching_cmds(const string& prefix, const char* array_of_matches[])
@@ -165,7 +165,7 @@ int find_all_matching_cmds(const string& prefix, const char* array_of_matches[])
 
 	for ( int i = 0; i < num_debug_cmds(); ++i )
 		{
-		array_of_matches[g_DebugCmdInfos[i]->Cmd()] = 0;
+		array_of_matches[g_DebugCmdInfos[i]->Cmd()] = nullptr;
 
 		for ( int j = 0; j < g_DebugCmdInfos[i]->NumNames(); ++j )
 			{
@@ -177,7 +177,7 @@ int find_all_matching_cmds(const string& prefix, const char* array_of_matches[])
 			if ( ! prefix.compare(curr_name) )
 				{
 				for ( int k = 0; k < num_debug_cmds(); ++k )
-					array_of_matches[k] = 0;
+					array_of_matches[k] = nullptr;
 
 				array_of_matches[g_DebugCmdInfos[i]->Cmd()] = curr_name;
 				return 1;
@@ -214,7 +214,7 @@ static int dbg_backtrace_internal(int start, int end)
 	for ( int i = start; i >= end; --i )
 		{
 		const Frame* f = g_frame_stack[i];
-		const Stmt* stmt = f ? f->GetNextStmt() : 0;
+		const Stmt* stmt = f ? f->GetNextStmt() : nullptr;
 
 		string context = get_context_description(stmt, f);
 		debug_msg("#%d  %s\n",
diff --git a/src/DebugCmds.h b/src/DebugCmds.h
index 470e4ae993..c5c84ad7fa 100644
--- a/src/DebugCmds.h
+++ b/src/DebugCmds.h
@@ -18,7 +18,7 @@ public:
 			bool resume_execution, const char* const helpstring,
 			bool repeatable);
 
-	DebugCmdInfo() : helpstring(0) {}
+	DebugCmdInfo() : helpstring(nullptr) {}
 
 	int Cmd() const		{ return cmd; }
 	int NumNames() const	{ return num_names; }
diff --git a/src/DebugLogger.cc b/src/DebugLogger.cc
index fdb57efc61..4fac89414e 100644
--- a/src/DebugLogger.cc
+++ b/src/DebugLogger.cc
@@ -26,7 +26,7 @@ DebugLogger::Stream DebugLogger::streams[NUM_DBGS] = {
 DebugLogger::DebugLogger()
 	{
 	verbose = false;
-	file = 0;
+	file = nullptr;
 	}
 
 DebugLogger::~DebugLogger()
diff --git a/src/Desc.cc b/src/Desc.cc
index 50d95f80c8..c02347f42f 100644
--- a/src/Desc.cc
+++ b/src/Desc.cc
@@ -21,7 +21,7 @@ ODesc::ODesc(desc_type t, BroFile* arg_f)
 	style = STANDARD_STYLE;
 	f = arg_f;
 
-	if ( f == 0 )
+	if ( f == nullptr )
 		{
 		size = DEFAULT_SIZE;
 		base = safe_malloc(size);
@@ -31,7 +31,7 @@ ODesc::ODesc(desc_type t, BroFile* arg_f)
 	else
 		{
 		offset = size = 0;
-		base = 0;
+		base = nullptr;
 		}
 
 	indent_level = 0;
diff --git a/src/Desc.h b/src/Desc.h
index 2a29c75a92..8896dbf52f 100644
--- a/src/Desc.h
+++ b/src/Desc.h
@@ -29,7 +29,7 @@ class BroType;
 
 class ODesc {
 public:
-	explicit ODesc(desc_type t=DESC_READABLE, BroFile* f=0);
+	explicit ODesc(desc_type t=DESC_READABLE, BroFile* f=nullptr);
 
 	~ODesc();
 
@@ -131,7 +131,7 @@ public:
 	byte_vec TakeBytes()
 		{
 		const void* t = base;
-		base = 0;
+		base = nullptr;
 		size = 0;
 
 		// Don't clear offset, as we want to still support
diff --git a/src/Dict.cc b/src/Dict.cc
index 369510f7b1..1f62908c5c 100644
--- a/src/Dict.cc
+++ b/src/Dict.cc
@@ -81,7 +81,7 @@ TEST_CASE("dict operation")
 	dict.Remove(key2);
 	CHECK(dict.Length() == 0);
 	uint32_t* lookup2 = dict.Lookup(key2);
-	CHECK(lookup2 == (uint32_t*)0);
+	CHECK(lookup2 == (uint32_t*)nullptr);
 	delete key2;
 
 	CHECK(dict.MaxLength() == 1);
@@ -132,7 +132,7 @@ TEST_CASE("dict nthentry")
 
 	// NthEntry returns null for unordered dicts
 	uint32_t* lookup = unordered.NthEntry(0);
-	CHECK(lookup == (uint32_t*)0);
+	CHECK(lookup == (uint32_t*)nullptr);
 
 	// Ordered dicts are based on order of insertion, nothing about the
 	// data itself
@@ -256,7 +256,7 @@ void Dictionary::DeInit()
 void* Dictionary::Lookup(const void* key, int key_size, hash_t hash) const
 	{
 	if ( ! tbl && ! tbl2 )
-		return 0;
+		return nullptr;
 
 	hash_t h;
 	PList<DictEntry>* chain;
@@ -280,7 +280,7 @@ void* Dictionary::Lookup(const void* key, int key_size, hash_t hash) const
 			}
 		}
 
-	return 0;
+	return nullptr;
 	}
 
 void* Dictionary::Insert(void* key, int key_size, hash_t hash, void* val,
@@ -314,7 +314,7 @@ void* Dictionary::Remove(const void* key, int key_size, hash_t hash,
 				bool dont_delete)
 	{
 	if ( ! tbl && ! tbl2 )
-		return 0;
+		return nullptr;
 
 	hash_t h;
 	PList<DictEntry>* chain;
@@ -334,7 +334,7 @@ void* Dictionary::Remove(const void* key, int key_size, hash_t hash,
 		}
 
 	if ( ! chain )
-		return 0;
+		return nullptr;
 
 	for ( int i = 0; i < chain->length(); ++i )
 		{
@@ -346,7 +346,7 @@ void* Dictionary::Remove(const void* key, int key_size, hash_t hash,
 			void* entry_value = DoRemove(entry, h, chain, i);
 
 			if ( dont_delete )
-				entry->key = 0;
+				entry->key = nullptr;
 
 			delete entry;
 			--*num_entries_ptr;
@@ -354,7 +354,7 @@ void* Dictionary::Remove(const void* key, int key_size, hash_t hash,
 			}
 		}
 
-	return 0;
+	return nullptr;
 	}
 
 void* Dictionary::DoRemove(DictEntry* entry, hash_t h,
@@ -395,7 +395,7 @@ void* Dictionary::DoRemove(DictEntry* entry, hash_t h,
 void* Dictionary::NthEntry(int n, const void*& key, int& key_len) const
 	{
 	if ( ! order || n < 0 || n >= Length() )
-		return 0;
+		return nullptr;
 
 	DictEntry* entry = (*order)[n];
 	key = entry->key;
@@ -419,8 +419,8 @@ void* Dictionary::NextEntry(HashKey*& h, IterCookie*& cookie, int return_hash) c
 		{
 		const_cast<PList<IterCookie>*>(&cookies)->remove(cookie);
 		delete cookie;
-		cookie = 0;
-		return 0;
+		cookie = nullptr;
+		return nullptr;
 		}
 
 	// If there are any inserted entries, return them first.
@@ -486,8 +486,8 @@ void* Dictionary::NextEntry(HashKey*& h, IterCookie*& cookie, int return_hash) c
 		// a better way?
 		const_cast<PList<IterCookie>*>(&cookies)->remove(cookie);
 		delete cookie;
-		cookie = 0;
-		return 0;
+		cookie = nullptr;
+		return nullptr;
 		}
 
 	entry = (*ttbl[b])[0];
@@ -604,7 +604,7 @@ void* Dictionary::Insert(DictEntry* new_entry, bool copy_key)
 			c->inserted.push_back(new_entry);
 		}
 
-	return 0;
+	return nullptr;
 	}
 
 int Dictionary::NextPrime(int n) const
@@ -665,7 +665,7 @@ void Dictionary::MoveChains()
 		if ( ! chain )
 			continue;
 
-		tbl[tbl_next_ind - 1] = 0;
+		tbl[tbl_next_ind - 1] = nullptr;
 
 		for ( int j = 0; j < chain->length(); ++j )
 			{
diff --git a/src/Dict.h b/src/Dict.h
index b5edeba76b..a611c1b3f1 100644
--- a/src/Dict.h
+++ b/src/Dict.h
@@ -70,7 +70,7 @@ public:
 		}
 
 	// True if the dictionary is ordered, false otherwise.
-	bool IsOrdered() const		{ return order != 0; }
+	bool IsOrdered() const		{ return order != nullptr; }
 
 	// If the dictionary is ordered then returns the n'th entry's value;
 	// the second method also returns the key.  The first entry inserted
diff --git a/src/EquivClass.cc b/src/EquivClass.cc
index c067137227..39bc2699c2 100644
--- a/src/EquivClass.cc
+++ b/src/EquivClass.cc
@@ -12,7 +12,7 @@ EquivClass::EquivClass(int arg_size)
 	bck = new int[size];
 	equiv_class = new int[size];
 	rep = new int[size];
-	ccl_flags = 0;
+	ccl_flags = nullptr;
 	num_ecs = 0;
 
 	ec_nil = no_class = no_rep = size + 1;
diff --git a/src/Event.cc b/src/Event.cc
index c33fba5929..11e34b0117 100644
--- a/src/Event.cc
+++ b/src/Event.cc
@@ -74,10 +74,10 @@ void Event::Dispatch(bool no_remote)
 
 EventMgr::EventMgr()
 	{
-	head = tail = 0;
+	head = tail = nullptr;
 	current_src = SOURCE_LOCAL;
 	current_aid = 0;
-	src_val = 0;
+	src_val = nullptr;
 	draining = false;
 	}
 
@@ -176,8 +176,8 @@ void EventMgr::Drain()
 	for ( int round = 0; head && round < 2; round++ )
 		{
 		Event* current = head;
-		head = 0;
-		tail = 0;
+		head = nullptr;
+		tail = nullptr;
 
 		while ( current )
 			{
diff --git a/src/Event.h b/src/Event.h
index 6bf43a0aa4..44ede22e66 100644
--- a/src/Event.h
+++ b/src/Event.h
@@ -64,7 +64,7 @@ public:
 	[[deprecated("Remove in v4.1.  Use Enqueue() instead.")]]
 	void QueueEventFast(const EventHandlerPtr &h, val_list vl,
 			SourceID src = SOURCE_LOCAL, analyzer::ID aid = 0,
-			TimerMgr* mgr = 0, BroObj* obj = 0);
+			TimerMgr* mgr = nullptr, BroObj* obj = nullptr);
 
 	// Queues an event if there's an event handler (or remote consumer).  This
 	// function always takes ownership of decrementing the reference count of
@@ -75,7 +75,7 @@ public:
 	[[deprecated("Remove in v4.1.  Use Enqueue() instead.")]]
 	void QueueEvent(const EventHandlerPtr &h, val_list vl,
 			SourceID src = SOURCE_LOCAL, analyzer::ID aid = 0,
-			TimerMgr* mgr = 0, BroObj* obj = 0);
+			TimerMgr* mgr = nullptr, BroObj* obj = nullptr);
 
 	// Same as QueueEvent, except taking the event's argument list via a
 	// pointer instead of by value.  This function takes ownership of the
@@ -84,7 +84,7 @@ public:
 	[[deprecated("Remove in v4.1.  Use Enqueue() instead.")]]
 	void QueueEvent(const EventHandlerPtr &h, val_list* vl,
 			SourceID src = SOURCE_LOCAL, analyzer::ID aid = 0,
-			TimerMgr* mgr = 0, BroObj* obj = 0);
+			TimerMgr* mgr = nullptr, BroObj* obj = nullptr);
 
 	/**
 	 * Adds an event to the queue.  If no handler is found for the event
@@ -117,7 +117,7 @@ public:
 	void Drain();
 	bool IsDraining() const	{ return draining; }
 
-	bool HasEvents() const	{ return head != 0; }
+	bool HasEvents() const	{ return head != nullptr; }
 
 	// Returns the source ID of last raised event.
 	SourceID CurrentSource() const	{ return current_src; }
diff --git a/src/EventHandler.cc b/src/EventHandler.cc
index 8f35d47ed5..c1fad45a91 100644
--- a/src/EventHandler.cc
+++ b/src/EventHandler.cc
@@ -13,8 +13,8 @@ EventHandler::EventHandler(const char* arg_name)
 	{
 	name = copy_string(arg_name);
 	used = false;
-	local = 0;
-	type = 0;
+	local = nullptr;
+	type = nullptr;
 	error_handler = false;
 	enabled = true;
 	generate_always = false;
@@ -42,10 +42,10 @@ FuncType* EventHandler::FType(bool check_export)
 	                    check_export);
 
 	if ( ! id )
-		return 0;
+		return nullptr;
 
 	if ( id->Type()->Tag() != TYPE_FUNC )
-		return 0;
+		return nullptr;
 
 	type = id->Type()->AsFuncType();
 	return type;
diff --git a/src/EventHandler.h b/src/EventHandler.h
index effafb134e..59773560f6 100644
--- a/src/EventHandler.h
+++ b/src/EventHandler.h
@@ -69,7 +69,7 @@ private:
 // Encapsulates a ptr to an event handler to overload the boolean operator.
 class EventHandlerPtr {
 public:
-	EventHandlerPtr(EventHandler* p = 0)		{ handler = p; }
+	EventHandlerPtr(EventHandler* p = nullptr)		{ handler = p; }
 	EventHandlerPtr(const EventHandlerPtr& h)	{ handler = h.handler; }
 
 	const EventHandlerPtr& operator=(EventHandler* p)
diff --git a/src/Expr.cc b/src/Expr.cc
index 0c99f01012..cb34859ea6 100644
--- a/src/Expr.cc
+++ b/src/Expr.cc
@@ -54,7 +54,7 @@ const char* expr_name(BroExprTag t)
 	return expr_names[int(t)];
 	}
 
-Expr::Expr(BroExprTag arg_tag) : tag(arg_tag), type(0), paren(false)
+Expr::Expr(BroExprTag arg_tag) : tag(arg_tag), type(nullptr), paren(false)
 	{
 	SetLocationInfo(&start_location, &end_location);
 	}
@@ -1623,7 +1623,7 @@ IntrusivePtr<Val> BoolExpr::Eval(Frame* f) const
 			result->Assign(i, val_mgr->GetBool(local_result));
 			}
 		else
-			result->Assign(i, 0);
+			result->Assign(i, nullptr);
 		}
 
 	return result;
@@ -1952,7 +1952,7 @@ IntrusivePtr<Val> CondExpr::Eval(Frame* f) const
 			result->Assign(i, v ? v->Ref() : nullptr);
 			}
 		else
-			result->Assign(i, 0);
+			result->Assign(i, nullptr);
 		}
 
 	return result;
@@ -2019,7 +2019,7 @@ AssignExpr::AssignExpr(IntrusivePtr<Expr> arg_op1, IntrusivePtr<Expr> arg_op2,
 	             std::move(arg_op1) : arg_op1->MakeLvalue(),
 	             std::move(arg_op2))
 	{
-	val = 0;
+	val = nullptr;
 	is_init = arg_is_init;
 
 	if ( IsError() )
@@ -2079,7 +2079,7 @@ bool AssignExpr::TypeCheck(attr_list* attrs)
 
 	if ( bt1 == TYPE_TABLE && op2->Tag() == EXPR_LIST )
 		{
-		attr_list* attr_copy = 0;
+		attr_list* attr_copy = nullptr;
 
 		if ( attrs )
 			{
@@ -2178,7 +2178,7 @@ bool AssignExpr::TypeCheck(attr_list* attrs)
 					return false;
 					}
 
-				attr_list* attr_copy = 0;
+				attr_list* attr_copy = nullptr;
 
 				if ( sce->Attrs() )
 					{
@@ -2293,7 +2293,7 @@ void AssignExpr::EvalIntoAggregate(const BroType* t, Val* aggr, Frame* f) const
 	if ( IsError() )
 		return;
 
-	TypeDecl td(0, 0);
+	TypeDecl td(nullptr, nullptr);
 
 	if ( IsRecordElement(&td) )
 		{
@@ -2348,7 +2348,7 @@ IntrusivePtr<Val> AssignExpr::InitVal(const BroType* t, IntrusivePtr<Val> aggr)
 	if ( IsError() )
 		return nullptr;
 
-	TypeDecl td(0, 0);
+	TypeDecl td(nullptr, nullptr);
 
 	if ( IsRecordElement(&td) )
 		{
@@ -2690,7 +2690,7 @@ IntrusivePtr<Val> IndexExpr::Fold(Val* v1, Val* v2) const
 		const ListVal* lv = v2->AsListVal();
 		const BroString* s = v1->AsString();
 		int len = s->Len();
-		BroString* substring = 0;
+		BroString* substring = nullptr;
 
 		if ( lv->Length() == 1 )
 			{
@@ -2709,7 +2709,7 @@ IntrusivePtr<Val> IndexExpr::Fold(Val* v1, Val* v2) const
 			bro_int_t substring_len = last - first;
 
 			if ( substring_len < 0 )
-				substring = 0;
+				substring = nullptr;
 			else
 				substring = s->GetSubstring(first, substring_len);
 			}
@@ -2851,7 +2851,7 @@ TraversalCode IndexExpr::Traverse(TraversalCallback* cb) const
 
 FieldExpr::FieldExpr(IntrusivePtr<Expr> arg_op, const char* arg_field_name)
 	: UnaryExpr(EXPR_FIELD, std::move(arg_op)),
-	  field_name(copy_string(arg_field_name)), td(0), field(0)
+	  field_name(copy_string(arg_field_name)), td(nullptr), field(0)
 	{
 	if ( IsError() )
 		return;
@@ -2905,7 +2905,7 @@ void FieldExpr::Assign(Frame* f, IntrusivePtr<Val> v)
 
 void FieldExpr::Delete(Frame* f)
 	{
-	Assign(f, 0);
+	Assign(f, nullptr);
 	}
 
 IntrusivePtr<Val> FieldExpr::Fold(Val* v) const
@@ -2914,7 +2914,7 @@ IntrusivePtr<Val> FieldExpr::Fold(Val* v) const
 		return {NewRef{}, result};
 
 	// Check for &default.
-	const Attr* def_attr = td ? td->FindAttr(ATTR_DEFAULT) : 0;
+	const Attr* def_attr = td ? td->FindAttr(ATTR_DEFAULT) : nullptr;
 
 	if ( def_attr )
 		return def_attr->AttrExpr()->Eval(nullptr);
@@ -3101,7 +3101,7 @@ TableConstructorExpr::TableConstructorExpr(IntrusivePtr<ListExpr> constructor_li
 			}
 		}
 
-	attrs = arg_attrs ? new Attributes(arg_attrs, type, false, false) : 0;
+	attrs = arg_attrs ? new Attributes(arg_attrs, type, false, false) : nullptr;
 
 	type_list* indices = type->AsTableType()->Indices()->Types();
 	const expr_list& cle = op->AsListExpr()->Exprs();
@@ -3173,7 +3173,7 @@ IntrusivePtr<Val> TableConstructorExpr::InitVal(const BroType* t, IntrusivePtr<V
 	const expr_list& exprs = op->AsListExpr()->Exprs();
 
 	for ( const auto& expr : exprs )
-		expr->EvalIntoAggregate(t, tval.get(), 0);
+		expr->EvalIntoAggregate(t, tval.get(), nullptr);
 
 	return tval;
 	}
@@ -3219,7 +3219,7 @@ SetConstructorExpr::SetConstructorExpr(IntrusivePtr<ListExpr> constructor_list,
 	else if ( type->Tag() != TYPE_TABLE || ! type->AsTableType()->IsSet() )
 		SetError("values in set(...) constructor do not specify a set");
 
-	attrs = arg_attrs ? new Attributes(arg_attrs, type, false, false) : 0;
+	attrs = arg_attrs ? new Attributes(arg_attrs, type, false, false) : nullptr;
 
 	type_list* indices = type->AsTableType()->Indices()->Types();
 	expr_list& cle = op->AsListExpr()->Exprs();
@@ -3265,7 +3265,7 @@ IntrusivePtr<Val> SetConstructorExpr::Eval(Frame* f) const
 	for ( const auto& expr : exprs )
 		{
 		auto element = expr->Eval(f);
-		aggr->Assign(element.get(), 0);
+		aggr->Assign(element.get(), nullptr);
 		}
 
 	return aggr;
@@ -3287,7 +3287,7 @@ IntrusivePtr<Val> SetConstructorExpr::InitVal(const BroType* t, IntrusivePtr<Val
 		{
 		auto element = check_and_promote(e->Eval(nullptr), index_type, true);
 
-		if ( ! element || ! tval->Assign(element.get(), 0) )
+		if ( ! element || ! tval->Assign(element.get(), nullptr) )
 			{
 			Error(fmt("initialization type mismatch in set"), e);
 			return nullptr;
@@ -3521,7 +3521,7 @@ IntrusivePtr<Val> ArithCoerceExpr::Fold(Val* v) const
 		if ( Val* elt = vv->Lookup(i) )
 			result->Assign(i, FoldSingleVal(elt, t));
 		else
-			result->Assign(i, 0);
+			result->Assign(i, nullptr);
 		}
 
 	return result;
@@ -4191,7 +4191,7 @@ IntrusivePtr<Val> CallExpr::Eval(Frame* f) const
 	if ( func_val && v )
 		{
 		const ::Func* funcv = func_val->AsFunc();
-		const CallExpr* current_call = f ? f->GetCall() : 0;
+		const CallExpr* current_call = f ? f->GetCall() : nullptr;
 
 		if ( f )
 			f->SetCall(this);
@@ -4491,12 +4491,12 @@ IntrusivePtr<BroType> ListExpr::InitType() const
 		return nullptr;
 		}
 
-	if ( exprs[0]->IsRecordElement(0) )
+	if ( exprs[0]->IsRecordElement(nullptr) )
 		{
 		type_decl_list* types = new type_decl_list(exprs.length());
 		for ( const auto& expr : exprs )
 			{
-			TypeDecl* td = new TypeDecl(0, 0);
+			TypeDecl* td = new TypeDecl(nullptr, nullptr);
 			if ( ! expr->IsRecordElement(td) )
 				{
 				expr->Error("record element expected");
@@ -5063,7 +5063,7 @@ bool check_and_promote_args(ListExpr* const args, RecordType* types)
 		for ( int i = ntypes - 1; i >= el.length(); --i )
 			{
 			TypeDecl* td = types->FieldDecl(i);
-			Attr* def_attr = td->attrs ? td->attrs->FindAttr(ATTR_DEFAULT) : 0;
+			Attr* def_attr = td->attrs ? td->attrs->FindAttr(ATTR_DEFAULT) : nullptr;
 
 			if ( ! def_attr )
 				{
diff --git a/src/Expr.h b/src/Expr.h
index 1ed01a57a9..4727b5c670 100644
--- a/src/Expr.h
+++ b/src/Expr.h
@@ -523,7 +523,7 @@ public:
 	bool IsPure() const override;
 
 protected:
-	bool TypeCheck(attr_list* attrs = 0);
+	bool TypeCheck(attr_list* attrs = nullptr);
 	bool TypeCheckArithmetics(TypeTag bt1, TypeTag bt2);
 
 	bool is_init;
diff --git a/src/File.cc b/src/File.cc
index ade6918715..7581b9fb3b 100644
--- a/src/File.cc
+++ b/src/File.cc
@@ -56,9 +56,9 @@ BroFile::BroFile(FILE* arg_f)
 	{
 	Init();
 	f = arg_f;
-	name = access = 0;
+	name = access = nullptr;
 	t = base_type(TYPE_STRING);
-	is_open = (f != 0);
+	is_open = (f != nullptr);
 	}
 
 BroFile::BroFile(FILE* arg_f, const char* arg_name, const char* arg_access)
@@ -68,13 +68,13 @@ BroFile::BroFile(FILE* arg_f, const char* arg_name, const char* arg_access)
 	name = copy_string(arg_name);
 	access = copy_string(arg_access);
 	t = base_type(TYPE_STRING);
-	is_open = (f != 0);
+	is_open = (f != nullptr);
 	}
 
 BroFile::BroFile(const char* arg_name, const char* arg_access)
 	{
 	Init();
-	f = 0;
+	f = nullptr;
 	name = copy_string(arg_name);
 	access = copy_string(arg_access);
 	t = base_type(TYPE_STRING);
@@ -110,7 +110,7 @@ const char* BroFile::Name() const
 	if ( f == stderr )
 		return "/dev/stderr";
 
-	return 0;
+	return nullptr;
 	}
 
 bool BroFile::Open(FILE* file, const char* mode)
@@ -168,7 +168,7 @@ void BroFile::Init()
 	{
 	open_time = 0;
 	is_open = false;
-	attrs = 0;
+	attrs = nullptr;
 	buffered = true;
 	raw_output = false;
 
@@ -185,7 +185,7 @@ FILE* BroFile::File()
 FILE* BroFile::Seek(long new_position)
 	{
 	if ( ! File() )
-		return 0;
+		return nullptr;
 
 	if ( fseek(f, new_position, SEEK_SET) < 0 )
 		reporter->Error("seek failed");
@@ -271,11 +271,11 @@ void BroFile::SetAttrs(Attributes* arg_attrs)
 RecordVal* BroFile::Rotate()
 	{
 	if ( ! is_open )
-		return 0;
+		return nullptr;
 
 	// Do not rotate stdin/stdout/stderr.
 	if ( f == stdin || f == stdout || f == stderr )
-		return 0;
+		return nullptr;
 
 	RecordVal* info = new RecordVal(rotate_info);
 	FILE* newf = rotate_file(name, info);
@@ -283,7 +283,7 @@ RecordVal* BroFile::Rotate()
 	if ( ! newf )
 		{
 		Unref(info);
-		return 0;
+		return nullptr;
 		}
 
 	info->Assign(2, make_intrusive<Val>(open_time, TYPE_TIME));
@@ -291,7 +291,7 @@ RecordVal* BroFile::Rotate()
 	Unlink();
 
  	fclose(f);
-	f = 0;
+	f = nullptr;
 
 	Open(newf);
 	return info;
diff --git a/src/File.h b/src/File.h
index 2d10237a76..c811a958be 100644
--- a/src/File.h
+++ b/src/File.h
@@ -80,7 +80,7 @@ protected:
 	 * If file is not given and mode is, the filename will be opened with that
 	 * access mode.
 	 */
-	bool Open(FILE* f = nullptr, const char* mode = 0);
+	bool Open(FILE* f = nullptr, const char* mode = nullptr);
 
 	void Unlink();
 
diff --git a/src/Frag.cc b/src/Frag.cc
index c571a039d5..c155a91f51 100644
--- a/src/Frag.cc
+++ b/src/Frag.cc
@@ -49,7 +49,7 @@ FragReassembler::FragReassembler(NetSessions* arg_s,
 		memcpy(proto_hdr, ip->IP6_Hdr(), proto_hdr_len);
 		}
 
-	reassembled_pkt = 0;
+	reassembled_pkt = nullptr;
 	frag_size = 0;	// flag meaning "not known"
 	next_proto = ip->NextProto();
 
@@ -59,7 +59,7 @@ FragReassembler::FragReassembler(NetSessions* arg_s,
 		timer_mgr->Add(expire_timer);
 		}
 	else
-		expire_timer = 0;
+		expire_timer = nullptr;
 
 	AddFragment(t, ip, pkt);
 	}
@@ -285,7 +285,7 @@ void FragReassembler::BlockInserted(DataBlockMap::const_iterator /* it */)
 		}
 
 	delete reassembled_pkt;
-	reassembled_pkt = 0;
+	reassembled_pkt = nullptr;
 
 	unsigned int version = ((const struct ip*)pkt_start)->ip_v;
 
@@ -318,7 +318,7 @@ void FragReassembler::Expire(double t)
 	{
 	block_list.Clear();
 	expire_timer->ClearReassembler();
-	expire_timer = 0;	// timer manager will delete it
+	expire_timer = nullptr;	// timer manager will delete it
 
 	sessions->Remove(this);
 	}
@@ -329,6 +329,6 @@ void FragReassembler::DeleteTimer()
 		{
 		expire_timer->ClearReassembler();
 		timer_mgr->Cancel(expire_timer);
-		expire_timer = 0;	// timer manager will delete it
+		expire_timer = nullptr;	// timer manager will delete it
 		}
 	}
diff --git a/src/Frag.h b/src/Frag.h
index 31d5ec5bd0..ca81c54887 100644
--- a/src/Frag.h
+++ b/src/Frag.h
@@ -32,7 +32,7 @@ public:
 
 	void Expire(double t);
 	void DeleteTimer();
-	void ClearTimer()	{ expire_timer = 0; }
+	void ClearTimer()	{ expire_timer = nullptr; }
 
 	const IP_Hdr* ReassembledPkt()	{ return reassembled_pkt; }
 	const FragReassemblerKey& Key() const	{ return key; }
@@ -63,7 +63,7 @@ public:
 	void Dispatch(double t, bool is_expire) override;
 
 	// Break the association between this timer and its creator.
-	void ClearReassembler()	{ f = 0; }
+	void ClearReassembler()	{ f = nullptr; }
 
 protected:
 	FragReassembler* f;
diff --git a/src/Frame.cc b/src/Frame.cc
index 1c093398dc..09e95dad33 100644
--- a/src/Frame.cc
+++ b/src/Frame.cc
@@ -136,7 +136,7 @@ void Frame::Reset(int startIdx)
 	for ( int i = startIdx; i < size; ++i )
 		{
 		UnrefElement(i);
-		frame[i] = 0;
+		frame[i] = nullptr;
 		}
 	}
 
@@ -159,7 +159,7 @@ void Frame::Describe(ODesc* d) const
 
 		for ( int i = 0; i < size; ++i )
 			 {
-			 d->Add(frame[i] != 0);
+			 d->Add(frame[i] != nullptr);
 			 d->SP();
 			 }
 		}
diff --git a/src/Frame.h b/src/Frame.h
index 0961290ab1..2a5acab11e 100644
--- a/src/Frame.h
+++ b/src/Frame.h
@@ -217,7 +217,7 @@ public:
 	trigger::Trigger* GetTrigger() const		{ return trigger.get(); }
 
 	void SetCall(const CallExpr* arg_call)	{ call = arg_call; }
-	void ClearCall()			{ call = 0; }
+	void ClearCall()			{ call = nullptr; }
 	const CallExpr* GetCall() const		{ return call; }
 
 	void SetDelayed()	{ delayed = true; }
diff --git a/src/Func.h b/src/Func.h
index c414e3ac85..3f75226c1a 100644
--- a/src/Func.h
+++ b/src/Func.h
@@ -97,7 +97,7 @@ public:
 
 	uint32_t GetUniqueFuncID() const { return unique_id; }
 	static Func* GetFuncPtrByID(uint32_t id)
-		{ return id >= unique_ids.size() ? 0 : unique_ids[id]; }
+		{ return id >= unique_ids.size() ? nullptr : unique_ids[id]; }
 
 protected:
 	Func();
@@ -205,7 +205,7 @@ public:
 	void Describe(ODesc* d) const override;
 
 protected:
-	BuiltinFunc()	{ func = 0; is_pure = 0; }
+	BuiltinFunc()	{ func = nullptr; is_pure = 0; }
 
 	built_in_func func;
 	bool is_pure;
diff --git a/src/ID.cc b/src/ID.cc
index e0caea3b2d..3494d8a175 100644
--- a/src/ID.cc
+++ b/src/ID.cc
@@ -25,7 +25,7 @@ ID::ID(const char* arg_name, IDScope arg_scope, bool arg_is_export)
 	scope = arg_scope;
 	is_export = arg_is_export;
 	is_option = false;
-	val = 0;
+	val = nullptr;
 	is_const = false;
 	is_enum_const = false;
 	is_type = false;
@@ -60,7 +60,7 @@ void ID::ClearVal()
 	if ( ! weak_ref )
 		Unref(val);
 
-	val = 0;
+	val = nullptr;
 	}
 
 void ID::SetVal(IntrusivePtr<Val> v, bool arg_weak_ref)
@@ -147,12 +147,12 @@ void ID::SetVal(IntrusivePtr<Expr> ev, init_class c)
 
 bool ID::IsRedefinable() const
 	{
-	return FindAttr(ATTR_REDEF) != 0;
+	return FindAttr(ATTR_REDEF) != nullptr;
 	}
 
 void ID::SetAttrs(IntrusivePtr<Attributes> a)
 	{
-	attrs = 0;
+	attrs = nullptr;
 	AddAttrs(std::move(a));
 	}
 
@@ -197,12 +197,12 @@ void ID::UpdateValAttrs()
 
 Attr* ID::FindAttr(attr_tag t) const
 	{
-	return attrs ? attrs->FindAttr(t) : 0;
+	return attrs ? attrs->FindAttr(t) : nullptr;
 	}
 
 bool ID::IsDeprecated() const
 	{
-	return FindAttr(ATTR_DEPRECATED) != 0;
+	return FindAttr(ATTR_DEPRECATED) != nullptr;
 	}
 
 void ID::MakeDeprecated(IntrusivePtr<Expr> deprecation)
diff --git a/src/ID.h b/src/ID.h
index ee96ea7845..b7cca8237d 100644
--- a/src/ID.h
+++ b/src/ID.h
@@ -41,8 +41,8 @@ public:
 	const BroType* Type() const	{ return type.get(); }
 
 	void MakeType()			{ is_type = true; }
-	BroType* AsType()		{ return is_type ? Type() : 0; }
-	const BroType* AsType() const	{ return is_type ? Type() : 0; }
+	BroType* AsType()		{ return is_type ? Type() : nullptr; }
+	const BroType* AsType() const	{ return is_type ? Type() : nullptr; }
 
 	// If weak_ref is false, the Val is assumed to be already ref'ed
 	// and will be deref'ed when the ID is deleted.
@@ -57,7 +57,7 @@ public:
 	void SetVal(IntrusivePtr<Val> v, init_class c);
 	void SetVal(IntrusivePtr<Expr> ev, init_class c);
 
-	bool HasVal() const		{ return val != 0; }
+	bool HasVal() const		{ return val != nullptr; }
 	Val* ID_Val()			{ return val; }
 	const Val* ID_Val() const	{ return val; }
 	void ClearVal();
@@ -90,7 +90,7 @@ public:
 
 	std::string GetDeprecationWarning() const;
 
-	void Error(const char* msg, const BroObj* o2 = 0);
+	void Error(const char* msg, const BroObj* o2 = nullptr);
 
 	void Describe(ODesc* d) const override;
 	// Adds type and value to description.
diff --git a/src/IP.cc b/src/IP.cc
index 65c34c8e40..019bec0790 100644
--- a/src/IP.cc
+++ b/src/IP.cc
@@ -13,26 +13,26 @@
 #include "BroString.h"
 #include "Reporter.h"
 
-static RecordType* ip4_hdr_type = 0;
-static RecordType* ip6_hdr_type = 0;
-static RecordType* ip6_ext_hdr_type = 0;
-static RecordType* ip6_option_type = 0;
-static RecordType* ip6_hopopts_type = 0;
-static RecordType* ip6_dstopts_type = 0;
-static RecordType* ip6_routing_type = 0;
-static RecordType* ip6_fragment_type = 0;
-static RecordType* ip6_ah_type = 0;
-static RecordType* ip6_esp_type = 0;
-static RecordType* ip6_mob_type = 0;
-static RecordType* ip6_mob_msg_type = 0;
-static RecordType* ip6_mob_brr_type = 0;
-static RecordType* ip6_mob_hoti_type = 0;
-static RecordType* ip6_mob_coti_type = 0;
-static RecordType* ip6_mob_hot_type = 0;
-static RecordType* ip6_mob_cot_type = 0;
-static RecordType* ip6_mob_bu_type = 0;
-static RecordType* ip6_mob_back_type = 0;
-static RecordType* ip6_mob_be_type = 0;
+static RecordType* ip4_hdr_type = nullptr;
+static RecordType* ip6_hdr_type = nullptr;
+static RecordType* ip6_ext_hdr_type = nullptr;
+static RecordType* ip6_option_type = nullptr;
+static RecordType* ip6_hopopts_type = nullptr;
+static RecordType* ip6_dstopts_type = nullptr;
+static RecordType* ip6_routing_type = nullptr;
+static RecordType* ip6_fragment_type = nullptr;
+static RecordType* ip6_ah_type = nullptr;
+static RecordType* ip6_esp_type = nullptr;
+static RecordType* ip6_mob_type = nullptr;
+static RecordType* ip6_mob_msg_type = nullptr;
+static RecordType* ip6_mob_brr_type = nullptr;
+static RecordType* ip6_mob_hoti_type = nullptr;
+static RecordType* ip6_mob_coti_type = nullptr;
+static RecordType* ip6_mob_hot_type = nullptr;
+static RecordType* ip6_mob_cot_type = nullptr;
+static RecordType* ip6_mob_bu_type = nullptr;
+static RecordType* ip6_mob_back_type = nullptr;
+static RecordType* ip6_mob_be_type = nullptr;
 
 static inline RecordType* hdrType(RecordType*& type, const char* name)
 	{
@@ -79,7 +79,7 @@ static VectorVal* BuildOptionsVal(const u_char* data, int len)
 
 RecordVal* IPv6_Hdr::BuildRecordVal(VectorVal* chain) const
 	{
-	RecordVal* rv = 0;
+	RecordVal* rv = nullptr;
 
 	switch ( type ) {
 	case IPPROTO_IPV6:
@@ -330,7 +330,7 @@ IPAddr IP_Hdr::DstAddr() const
 
 RecordVal* IP_Hdr::BuildIPHdrVal() const
 	{
-	RecordVal* rval = 0;
+	RecordVal* rval = nullptr;
 
 	if ( ip4 )
 		{
@@ -354,7 +354,7 @@ RecordVal* IP_Hdr::BuildIPHdrVal() const
 
 RecordVal* IP_Hdr::BuildPktHdrVal() const
 	{
-	static RecordType* pkt_hdr_type = 0;
+	static RecordType* pkt_hdr_type = nullptr;
 
 	if ( ! pkt_hdr_type )
 		pkt_hdr_type = internal_type("pkt_hdr")->AsRecordType();
@@ -365,9 +365,9 @@ RecordVal* IP_Hdr::BuildPktHdrVal() const
 
 RecordVal* IP_Hdr::BuildPktHdrVal(RecordVal* pkt_hdr, int sindex) const
 	{
-	static RecordType* tcp_hdr_type = 0;
-	static RecordType* udp_hdr_type = 0;
-	static RecordType* icmp_hdr_type = 0;
+	static RecordType* tcp_hdr_type = nullptr;
+	static RecordType* udp_hdr_type = nullptr;
+	static RecordType* icmp_hdr_type = nullptr;
 
 	if ( ! tcp_hdr_type )
 		{
diff --git a/src/IP.h b/src/IP.h
index 287bcf8fad..5eaac66a2b 100644
--- a/src/IP.h
+++ b/src/IP.h
@@ -136,7 +136,7 @@ public:
 	/**
 	 * Returns the script-layer record representation of the header.
 	 */
-	RecordVal* BuildRecordVal(VectorVal* chain = 0) const;
+	RecordVal* BuildRecordVal(VectorVal* chain = nullptr) const;
 
 protected:
 	uint8_t type;
@@ -184,7 +184,7 @@ public:
 	 */
 	const struct ip6_frag* GetFragHdr() const
 		{ return IsFragment() ?
-				(const struct ip6_frag*)chain[chain.size()-1]->Data(): 0; }
+				(const struct ip6_frag*)chain[chain.size()-1]->Data(): nullptr; }
 
 	/**
 	 * If the header chain is a fragment, returns the offset in number of bytes
diff --git a/src/NFA.cc b/src/NFA.cc
index f22b4e0b21..94de8260d7 100644
--- a/src/NFA.cc
+++ b/src/NFA.cc
@@ -14,11 +14,11 @@ static int nfa_state_id = 0;
 NFA_State::NFA_State(int arg_sym, EquivClass* ec)
 	{
 	sym = arg_sym;
-	ccl = 0;
+	ccl = nullptr;
 	accept = NO_ACCEPT;
 	first_trans_is_back_ref = false;
-	mark = 0;
-	epsclosure = 0;
+	mark = nullptr;
+	epsclosure = nullptr;
 	id = ++nfa_state_id;
 
 	// Fix up equivalence classes based on this transition.  Note that any
@@ -39,9 +39,9 @@ NFA_State::NFA_State(CCL* arg_ccl)
 	ccl = arg_ccl;
 	accept = NO_ACCEPT;
 	first_trans_is_back_ref = false;
-	mark = 0;
+	mark = nullptr;
 	id = ++nfa_state_id;
-	epsclosure = 0;
+	epsclosure = nullptr;
 	}
 
 NFA_State::~NFA_State()
@@ -67,7 +67,7 @@ NFA_State* NFA_State::DeepCopy()
 		return mark;
 		}
 
-	NFA_State* copy = ccl ? new NFA_State(ccl) : new NFA_State(sym, 0);
+	NFA_State* copy = ccl ? new NFA_State(ccl) : new NFA_State(sym, nullptr);
 	SetMark(copy);
 
 	for ( int i = 0; i < xtions.length(); ++i )
@@ -80,7 +80,7 @@ void NFA_State::ClearMarks()
 	{
 	if ( mark )
 		{
-		SetMark(0);
+		SetMark(nullptr);
 		for ( int i = 0; i < xtions.length(); ++i )
 			xtions[i]->ClearMarks();
 		}
@@ -125,7 +125,7 @@ NFA_state_list* NFA_State::EpsilonClosure()
 
 	// Clear out markers.
 	for ( i = 0; i < states.length(); ++i )
-		states[i]->SetMark(0);
+		states[i]->SetMark(nullptr);
 
 	// Make it fit.
 	epsclosure->resize(0);
@@ -262,7 +262,7 @@ void NFA_Machine::MakePositiveClosure()
 
 void NFA_Machine::MakeRepl(int lower, int upper)
 	{
-	NFA_Machine* dup = 0;
+	NFA_Machine* dup = nullptr;
 	if ( upper > lower || upper == NO_UPPER_BOUND )
 		dup = DuplicateMachine();
 
diff --git a/src/NFA.h b/src/NFA.h
index 6b6827acc2..77e0102fba 100644
--- a/src/NFA.h
+++ b/src/NFA.h
@@ -78,12 +78,12 @@ protected:
 
 class EpsilonState : public NFA_State {
 public:
-	EpsilonState()	: NFA_State(SYM_EPSILON, 0)	{ }
+	EpsilonState()	: NFA_State(SYM_EPSILON, nullptr)	{ }
 };
 
 class NFA_Machine : public BroObj {
 public:
-	explicit NFA_Machine(NFA_State* first, NFA_State* final = 0);
+	explicit NFA_Machine(NFA_State* first, NFA_State* final = nullptr);
 	~NFA_Machine() override;
 
 	NFA_State* FirstState() const	{ return first_state; }
diff --git a/src/Net.cc b/src/Net.cc
index 6aa3177639..21542aad04 100644
--- a/src/Net.cc
+++ b/src/Net.cc
@@ -115,7 +115,7 @@ RETSIGTYPE watchdog(int /* signo */)
 					if ( ! pkt_dumper || pkt_dumper->IsError() )
 						{
 						reporter->Error("watchdog: can't open watchdog-pkt.pcap for writing");
-						pkt_dumper = 0;
+						pkt_dumper = nullptr;
 						}
 					}
 
diff --git a/src/Net.h b/src/Net.h
index e7b7f3bd7f..dc121ec9e0 100644
--- a/src/Net.h
+++ b/src/Net.h
@@ -30,7 +30,7 @@ extern void net_delete();	// Reclaim all memory, etc.
 extern void net_update_time(double new_network_time);
 extern void net_packet_dispatch(double t, const Packet* pkt,
 			iosource::PktSrc* src_ps);
-extern void expire_timers(iosource::PktSrc* src_ps = 0);
+extern void expire_timers(iosource::PktSrc* src_ps = nullptr);
 extern void zeek_terminate_loop(const char* reason);
 
 // Functions to temporarily suspend processing of live input (network packets
diff --git a/src/Obj.cc b/src/Obj.cc
index 43cee1e7d6..89edc8edff 100644
--- a/src/Obj.cc
+++ b/src/Obj.cc
@@ -165,7 +165,7 @@ void BroObj::DoMsg(ODesc* d, const char s1[], const BroObj* obj2,
 	d->Add(s1);
 	PinPoint(d, obj2, pinpoint_only);
 
-	const Location* loc2 = 0;
+	const Location* loc2 = nullptr;
 	if ( obj2 && obj2->GetLocationInfo() != &no_location &&
 		 *obj2->GetLocationInfo() != *GetLocationInfo() )
 		loc2 = obj2->GetLocationInfo();
diff --git a/src/Obj.h b/src/Obj.h
index ec09dd8571..cab0ab92d5 100644
--- a/src/Obj.h
+++ b/src/Obj.h
@@ -66,7 +66,7 @@ public:
 		// we check for whether start_location has a line number
 		// of 0, which should only happen if it's been assigned
 		// to no_location (or hasn't been initialized at all).
-		location = 0;
+		location = nullptr;
 		if ( start_location.first_line != 0 )
 			SetLocationInfo(&start_location, &end_location);
 		}
@@ -80,14 +80,14 @@ public:
 	// Report user warnings/errors.  If obj2 is given, then it's
 	// included in the message, though if pinpoint_only is non-zero,
 	// then obj2 is only used to pinpoint the location.
-	void Warn(const char* msg, const BroObj* obj2 = 0,
-			bool pinpoint_only = false, const Location* expr_location = 0) const;
-	void Error(const char* msg, const BroObj* obj2 = 0,
-			bool pinpoint_only = false, const Location* expr_location = 0) const;
+	void Warn(const char* msg, const BroObj* obj2 = nullptr,
+			bool pinpoint_only = false, const Location* expr_location = nullptr) const;
+	void Error(const char* msg, const BroObj* obj2 = nullptr,
+			bool pinpoint_only = false, const Location* expr_location = nullptr) const;
 
 	// Report internal errors.
-	void BadTag(const char* msg, const char* t1 = 0,
-			const char* t2 = 0) const;
+	void BadTag(const char* msg, const char* t1 = nullptr,
+			const char* t2 = nullptr) const;
 #define CHECK_TAG(t1, t2, text, tag_to_text_func) \
 	{ \
 	if ( t1 != t2 ) \
@@ -134,9 +134,9 @@ protected:
 private:
 	friend class SuppressErrors;
 
-	void DoMsg(ODesc* d, const char s1[], const BroObj* obj2 = 0,
-			bool pinpoint_only = false, const Location* expr_location = 0) const;
-	void PinPoint(ODesc* d, const BroObj* obj2 = 0,
+	void DoMsg(ODesc* d, const char s1[], const BroObj* obj2 = nullptr,
+			bool pinpoint_only = false, const Location* expr_location = nullptr) const;
+	void PinPoint(ODesc* d, const BroObj* obj2 = nullptr,
 			bool pinpoint_only = false) const;
 
 	friend inline void Ref(BroObj* o);
diff --git a/src/OpaqueVal.cc b/src/OpaqueVal.cc
index b8d7669d54..607376ed60 100644
--- a/src/OpaqueVal.cc
+++ b/src/OpaqueVal.cc
@@ -699,24 +699,24 @@ bool EntropyVal::DoUnserialize(const broker::data& data)
 BloomFilterVal::BloomFilterVal()
 	: OpaqueVal(bloomfilter_type)
 	{
-	type = 0;
-	hash = 0;
-	bloom_filter = 0;
+	type = nullptr;
+	hash = nullptr;
+	bloom_filter = nullptr;
 	}
 
 BloomFilterVal::BloomFilterVal(OpaqueType* t)
 	: OpaqueVal(t)
 	{
-	type = 0;
-	hash = 0;
-	bloom_filter = 0;
+	type = nullptr;
+	hash = nullptr;
+	bloom_filter = nullptr;
 	}
 
 BloomFilterVal::BloomFilterVal(probabilistic::BloomFilter* bf)
 	: OpaqueVal(bloomfilter_type)
 	{
-	type = 0;
-	hash = 0;
+	type = nullptr;
+	hash = nullptr;
 	bloom_filter = bf;
 	}
 
@@ -790,13 +790,13 @@ IntrusivePtr<BloomFilterVal> BloomFilterVal::Merge(const BloomFilterVal* x,
 	     ! same_type(x->Type(), y->Type()) )
 		{
 		reporter->Error("cannot merge Bloom filters with different types");
-		return 0;
+		return nullptr;
 		}
 
 	if ( typeid(*x->bloom_filter) != typeid(*y->bloom_filter) )
 		{
 		reporter->Error("cannot merge different Bloom filter types");
-		return 0;
+		return nullptr;
 		}
 
 	probabilistic::BloomFilter* copy = x->bloom_filter->Clone();
@@ -805,7 +805,7 @@ IntrusivePtr<BloomFilterVal> BloomFilterVal::Merge(const BloomFilterVal* x,
 		{
 		delete copy;
 		reporter->Error("failed to merge Bloom filter");
-		return 0;
+		return nullptr;
 		}
 
 	auto merged = make_intrusive<BloomFilterVal>(copy);
@@ -813,7 +813,7 @@ IntrusivePtr<BloomFilterVal> BloomFilterVal::Merge(const BloomFilterVal* x,
 	if ( x->Type() && ! merged->Typify(x->Type()) )
 		{
 		reporter->Error("failed to set type on merged Bloom filter");
-		return 0;
+		return nullptr;
 		}
 
 	return merged;
@@ -876,17 +876,17 @@ bool BloomFilterVal::DoUnserialize(const broker::data& data)
 
 CardinalityVal::CardinalityVal() : OpaqueVal(cardinality_type)
 	{
-	c = 0;
-	type = 0;
-	hash = 0;
+	c = nullptr;
+	type = nullptr;
+	hash = nullptr;
 	}
 
 CardinalityVal::CardinalityVal(probabilistic::CardinalityCounter* arg_c)
 	: OpaqueVal(cardinality_type)
 	{
 	c = arg_c;
-	type = 0;
-	hash = 0;
+	type = nullptr;
+	hash = nullptr;
 	}
 
 CardinalityVal::~CardinalityVal()
diff --git a/src/Options.cc b/src/Options.cc
index c4f864189a..a68f76595c 100644
--- a/src/Options.cc
+++ b/src/Options.cc
@@ -186,49 +186,49 @@ zeek::Options zeek::parse_cmdline(int argc, char** argv)
 		}
 
 	constexpr struct option long_opts[] = {
-		{"parse-only",	no_argument,		0,	'a'},
-		{"bare-mode",	no_argument,		0,	'b'},
-		{"debug-script",	no_argument,		0,	'd'},
-		{"exec",		required_argument,	0,	'e'},
-		{"filter",		required_argument,	0,	'f'},
-		{"help",		no_argument,		0,	'h'},
-		{"iface",		required_argument,	0,	'i'},
-		{"zeekygen",		required_argument,		0,	'X'},
-		{"prefix",		required_argument,	0,	'p'},
-		{"readfile",		required_argument,	0,	'r'},
-		{"rulefile",		required_argument,	0,	's'},
-		{"tracefile",		required_argument,	0,	't'},
-		{"writefile",		required_argument,	0,	'w'},
-		{"version",		no_argument,		0,	'v'},
-		{"no-checksums",	no_argument,		0,	'C'},
-		{"force-dns",		no_argument,		0,	'F'},
-		{"load-seeds",		required_argument,	0,	'G'},
-		{"save-seeds",		required_argument,	0,	'H'},
-		{"print-plugins",	no_argument,		0,	'N'},
-		{"prime-dns",		no_argument,		0,	'P'},
-		{"time",		no_argument,		0,	'Q'},
-		{"debug-rules",		no_argument,		0,	'S'},
-		{"re-level",		required_argument,	0,	'T'},
-		{"watchdog",		no_argument,		0,	'W'},
-		{"print-id",		required_argument,	0,	'I'},
-		{"status-file",		required_argument,	0,	'U'},
+		{"parse-only",	no_argument,		nullptr,	'a'},
+		{"bare-mode",	no_argument,		nullptr,	'b'},
+		{"debug-script",	no_argument,		nullptr,	'd'},
+		{"exec",		required_argument,	nullptr,	'e'},
+		{"filter",		required_argument,	nullptr,	'f'},
+		{"help",		no_argument,		nullptr,	'h'},
+		{"iface",		required_argument,	nullptr,	'i'},
+		{"zeekygen",		required_argument,		nullptr,	'X'},
+		{"prefix",		required_argument,	nullptr,	'p'},
+		{"readfile",		required_argument,	nullptr,	'r'},
+		{"rulefile",		required_argument,	nullptr,	's'},
+		{"tracefile",		required_argument,	nullptr,	't'},
+		{"writefile",		required_argument,	nullptr,	'w'},
+		{"version",		no_argument,		nullptr,	'v'},
+		{"no-checksums",	no_argument,		nullptr,	'C'},
+		{"force-dns",		no_argument,		nullptr,	'F'},
+		{"load-seeds",		required_argument,	nullptr,	'G'},
+		{"save-seeds",		required_argument,	nullptr,	'H'},
+		{"print-plugins",	no_argument,		nullptr,	'N'},
+		{"prime-dns",		no_argument,		nullptr,	'P'},
+		{"time",		no_argument,		nullptr,	'Q'},
+		{"debug-rules",		no_argument,		nullptr,	'S'},
+		{"re-level",		required_argument,	nullptr,	'T'},
+		{"watchdog",		no_argument,		nullptr,	'W'},
+		{"print-id",		required_argument,	nullptr,	'I'},
+		{"status-file",		required_argument,	nullptr,	'U'},
 
 #ifdef	DEBUG
-		{"debug",		required_argument,	0,	'B'},
+		{"debug",		required_argument,	nullptr,	'B'},
 #endif
 #ifdef	USE_IDMEF
-		{"idmef-dtd",		required_argument,	0,	'n'},
+		{"idmef-dtd",		required_argument,	nullptr,	'n'},
 #endif
 #ifdef	USE_PERFTOOLS_DEBUG
-		{"mem-leaks",	no_argument,		0,	'm'},
-		{"mem-profile",	no_argument,		0,	'M'},
+		{"mem-leaks",	no_argument,		nullptr,	'm'},
+		{"mem-profile",	no_argument,		nullptr,	'M'},
 #endif
 
-		{"pseudo-realtime",	optional_argument, 0,	'E'},
-		{"jobs",	optional_argument, 0,	'j'},
-		{"test",		no_argument,		0,	'#'},
+		{"pseudo-realtime",	optional_argument, nullptr,	'E'},
+		{"jobs",	optional_argument, nullptr,	'j'},
+		{"test",		no_argument,		nullptr,	'#'},
 
-		{0,			0,			0,	0},
+		{nullptr,			0,			nullptr,	0},
 	};
 
 	char opts[256];
diff --git a/src/PolicyFile.cc b/src/PolicyFile.cc
index a6f93c8d88..470194b3a1 100644
--- a/src/PolicyFile.cc
+++ b/src/PolicyFile.cc
@@ -18,8 +18,8 @@ using namespace std;
 #include "Reporter.h"
 
 struct PolicyFile {
-	PolicyFile ()	{ filedata = 0; lmtime = 0; }
-	~PolicyFile ()	{ delete [] filedata; filedata = 0; }
+	PolicyFile ()	{ filedata = nullptr; lmtime = 0; }
+	~PolicyFile ()	{ delete [] filedata; filedata = nullptr; }
 
 	time_t lmtime;
 	char* filedata;
diff --git a/src/PrefixTable.cc b/src/PrefixTable.cc
index 391d11e673..36012af5a3 100644
--- a/src/PrefixTable.cc
+++ b/src/PrefixTable.cc
@@ -28,7 +28,7 @@ void* PrefixTable::Insert(const IPAddr& addr, int width, void* data)
 	if ( ! node )
 		{
 		reporter->InternalWarning("Cannot create node in patricia tree");
-		return 0;
+		return nullptr;
 		}
 
 	void* old = node->data;
@@ -59,7 +59,7 @@ void* PrefixTable::Insert(const Val* value, void* data)
 
 	default:
 		reporter->InternalWarning("Wrong index type for PrefixTable");
-		return 0;
+		return nullptr;
 	}
 	}
 
@@ -97,7 +97,7 @@ void* PrefixTable::Lookup(const IPAddr& addr, int width, bool exact) const
 	patricia_node_t** list = nullptr;
 
 	Deref_Prefix(prefix);
-	return node ? node->data : 0;
+	return node ? node->data : nullptr;
 	}
 
 void* PrefixTable::Lookup(const Val* value, bool exact) const
@@ -120,7 +120,7 @@ void* PrefixTable::Lookup(const Val* value, bool exact) const
 	default:
 		reporter->InternalWarning("Wrong index type %d for PrefixTable",
 		                          value->Type()->Tag());
-		return 0;
+		return nullptr;
 	}
 	}
 
@@ -131,7 +131,7 @@ void* PrefixTable::Remove(const IPAddr& addr, int width)
 	Deref_Prefix(prefix);
 
 	if ( ! node )
-		return 0;
+		return nullptr;
 
 	void* old = node->data;
 	patricia_remove(tree, node);
@@ -158,7 +158,7 @@ void* PrefixTable::Remove(const Val* value)
 
 	default:
 		reporter->InternalWarning("Wrong index type for PrefixTable");
-		return 0;
+		return nullptr;
 	}
 	}
 
@@ -167,7 +167,7 @@ PrefixTable::iterator PrefixTable::InitIterator()
 	iterator i;
 	i.Xsp = i.Xstack;
 	i.Xrn = tree->head;
-	i.Xnode = 0;
+	i.Xnode = nullptr;
 	return i;
 	}
 
@@ -177,7 +177,7 @@ void* PrefixTable::GetNext(iterator* i)
 		{
 		i->Xnode = i->Xrn;
 		if ( ! i->Xnode )
-			return 0;
+			return nullptr;
 
 		if ( i->Xrn->l )
 			{
@@ -194,7 +194,7 @@ void* PrefixTable::GetNext(iterator* i)
 			i->Xrn = *(--i->Xsp);
 
 		else
-			i->Xrn = (patricia_node_t*) 0;
+			i->Xrn = (patricia_node_t*) nullptr;
 
 		if ( i->Xnode->prefix )
 			return (void*) i->Xnode->data;
diff --git a/src/PrefixTable.h b/src/PrefixTable.h
index 21b956756a..2bd640772d 100644
--- a/src/PrefixTable.h
+++ b/src/PrefixTable.h
@@ -30,10 +30,10 @@ public:
 	// Addr in network byte order. If data is zero, acts like a set.
 	// Returns ptr to old data if already existing.
 	// For existing items without data, returns non-nil if found.
-	void* Insert(const IPAddr& addr, int width, void* data = 0);
+	void* Insert(const IPAddr& addr, int width, void* data = nullptr);
 
 	// Value may be addr or subnet.
-	void* Insert(const Val* value, void* data = 0);
+	void* Insert(const Val* value, void* data = nullptr);
 
 	// Returns nil if not found, pointer to data otherwise.
 	// For items without data, returns non-nil if found.
diff --git a/src/PriorityQueue.h b/src/PriorityQueue.h
index 05de50ee69..591c79c474 100644
--- a/src/PriorityQueue.h
+++ b/src/PriorityQueue.h
@@ -34,7 +34,7 @@ public:
 	PQ_Element* Top() const
 		{
 		if ( heap_size == 0 )
-			return 0;
+			return nullptr;
 
 		return heap[0];
 		}
diff --git a/src/RE.cc b/src/RE.cc
index 183c421e17..ac59567f4d 100644
--- a/src/RE.cc
+++ b/src/RE.cc
@@ -12,10 +12,10 @@
 #include "Reporter.h"
 #include "BroString.h"
 
-CCL* curr_ccl = 0;
+CCL* curr_ccl = nullptr;
 
 Specific_RE_Matcher* rem;
-NFA_Machine* nfa = 0;
+NFA_Machine* nfa = nullptr;
 int case_insensitive = 0;
 
 extern int RE_parse(void);
@@ -27,10 +27,10 @@ Specific_RE_Matcher::Specific_RE_Matcher(match_type arg_mt, int arg_multiline)
 	{
 	mt = arg_mt;
 	multiline = arg_multiline;
-	any_ccl = 0;
-	pattern_text = 0;
-	dfa = 0;
-	ecs = 0;
+	any_ccl = nullptr;
+	pattern_text = nullptr;
+	dfa = nullptr;
+	ecs = nullptr;
 	accepted = new AcceptingSet();
 	}
 
@@ -131,7 +131,7 @@ bool Specific_RE_Matcher::Compile(bool lazy)
 		{
 		reporter->Error("error compiling pattern /%s/", pattern_text);
 		Unref(nfa);
-		nfa = 0;
+		nfa = nullptr;
 		return false;
 		}
 
@@ -141,7 +141,7 @@ bool Specific_RE_Matcher::Compile(bool lazy)
 	dfa = new DFA_Machine(nfa, EC());
 
 	Unref(nfa);
-	nfa = 0;
+	nfa = nullptr;
 
 	ecs = EC()->EquivClasses();
 
@@ -155,7 +155,7 @@ bool Specific_RE_Matcher::CompileSet(const string_list& set, const int_list& idx
 
 	rem = this;
 
-	NFA_Machine* set_nfa = 0;
+	NFA_Machine* set_nfa = nullptr;
 
 	loop_over_list(set, i)
 		{
@@ -172,7 +172,7 @@ bool Specific_RE_Matcher::CompileSet(const string_list& set, const int_list& idx
 			else
 				Unref(nfa);
 
-			nfa = 0;
+			nfa = nullptr;
 			return false;
 			}
 
@@ -257,7 +257,7 @@ bool Specific_RE_Matcher::MatchAll(const u_char* bv, int n)
 	if ( d )
 		d = d->Xtion(ecs[SYM_EOL], dfa);
 
-	return d && d->Accept() != 0;
+	return d && d->Accept() != nullptr;
 	}
 
 
@@ -354,7 +354,7 @@ bool RE_Match_State::Match(const u_char* bv, int n,
 
 		if ( ! next_state )
 			{
-			current_state = 0;
+			current_state = nullptr;
 			break;
 			}
 
diff --git a/src/RE.h b/src/RE.h
index 702767016c..dfadcaaf28 100644
--- a/src/RE.h
+++ b/src/RE.h
@@ -140,10 +140,10 @@ class RE_Match_State {
 public:
 	explicit RE_Match_State(Specific_RE_Matcher* matcher)
 		{
-		dfa = matcher->DFA() ? matcher->DFA() : 0;
+		dfa = matcher->DFA() ? matcher->DFA() : nullptr;
 		ecs = matcher->EC()->EquivClasses();
 		current_pos = -1;
-		current_state = 0;
+		current_state = nullptr;
 		}
 
 	const AcceptingMatchSet& AcceptedMatches() const
@@ -159,7 +159,7 @@ public:
 	void Clear()
 		{
 		current_pos = -1;
-		current_state = 0;
+		current_state = nullptr;
 		accepted_matches.clear();
 		}
 
diff --git a/src/Reporter.cc b/src/Reporter.cc
index 68446dd553..ae5261ff5f 100644
--- a/src/Reporter.cc
+++ b/src/Reporter.cc
@@ -30,7 +30,7 @@ int closelog();
 }
 #endif
 
-Reporter* reporter = 0;
+Reporter* reporter = nullptr;
 
 Reporter::Reporter()
 	{
@@ -88,8 +88,8 @@ void Reporter::Info(const char* fmt, ...)
 	{
 	va_list ap;
 	va_start(ap, fmt);
-	FILE* out = EmitToStderr(info_to_stderr) ? stderr : 0;
-	DoLog("", reporter_info, out, 0, 0, true, true, 0, fmt, ap);
+	FILE* out = EmitToStderr(info_to_stderr) ? stderr : nullptr;
+	DoLog("", reporter_info, out, nullptr, nullptr, true, true, nullptr, fmt, ap);
 	va_end(ap);
 	}
 
@@ -97,8 +97,8 @@ void Reporter::Warning(const char* fmt, ...)
 	{
 	va_list ap;
 	va_start(ap, fmt);
-	FILE* out = EmitToStderr(warnings_to_stderr) ? stderr : 0;
-	DoLog("warning", reporter_warning, out, 0, 0, true, true, 0, fmt, ap);
+	FILE* out = EmitToStderr(warnings_to_stderr) ? stderr : nullptr;
+	DoLog("warning", reporter_warning, out, nullptr, nullptr, true, true, nullptr, fmt, ap);
 	va_end(ap);
 	}
 
@@ -107,8 +107,8 @@ void Reporter::Error(const char* fmt, ...)
 	++errors;
 	va_list ap;
 	va_start(ap, fmt);
-	FILE* out = EmitToStderr(errors_to_stderr) ? stderr : 0;
-	DoLog("error", reporter_error, out, 0, 0, true, true, 0, fmt, ap);
+	FILE* out = EmitToStderr(errors_to_stderr) ? stderr : nullptr;
+	DoLog("error", reporter_error, out, nullptr, nullptr, true, true, nullptr, fmt, ap);
 	va_end(ap);
 	}
 
@@ -118,7 +118,7 @@ void Reporter::FatalError(const char* fmt, ...)
 	va_start(ap, fmt);
 
 	// Always log to stderr.
-	DoLog("fatal error", 0, stderr, 0, 0, true, false, 0, fmt, ap);
+	DoLog("fatal error", nullptr, stderr, nullptr, nullptr, true, false, nullptr, fmt, ap);
 
 	va_end(ap);
 
@@ -134,7 +134,7 @@ void Reporter::FatalErrorWithCore(const char* fmt, ...)
 	va_start(ap, fmt);
 
 	// Always log to stderr.
-	DoLog("fatal error", 0, stderr, 0, 0, true, false, 0, fmt, ap);
+	DoLog("fatal error", nullptr, stderr, nullptr, nullptr, true, false, nullptr, fmt, ap);
 
 	va_end(ap);
 
@@ -152,8 +152,8 @@ void Reporter::ExprRuntimeError(const Expr* expr, const char* fmt, ...)
 	PushLocation(expr->GetLocationInfo());
 	va_list ap;
 	va_start(ap, fmt);
-	FILE* out = EmitToStderr(errors_to_stderr) ? stderr : 0;
-	DoLog("expression error", reporter_error, out, 0, 0, true, true,
+	FILE* out = EmitToStderr(errors_to_stderr) ? stderr : nullptr;
+	DoLog("expression error", reporter_error, out, nullptr, nullptr, true, true,
 	      d.Description(), fmt, ap);
 	va_end(ap);
 	PopLocation();
@@ -166,8 +166,8 @@ void Reporter::RuntimeError(const Location* location, const char* fmt, ...)
 	PushLocation(location);
 	va_list ap;
 	va_start(ap, fmt);
-	FILE* out = EmitToStderr(errors_to_stderr) ? stderr : 0;
-	DoLog("runtime error", reporter_error, out, 0, 0, true, true, "", fmt, ap);
+	FILE* out = EmitToStderr(errors_to_stderr) ? stderr : nullptr;
+	DoLog("runtime error", reporter_error, out, nullptr, nullptr, true, true, "", fmt, ap);
 	va_end(ap);
 	PopLocation();
 	throw InterpreterException();
@@ -179,7 +179,7 @@ void Reporter::InternalError(const char* fmt, ...)
 	va_start(ap, fmt);
 
 	// Always log to stderr.
-	DoLog("internal error", 0, stderr, 0, 0, true, false, 0, fmt, ap);
+	DoLog("internal error", nullptr, stderr, nullptr, nullptr, true, false, nullptr, fmt, ap);
 
 	va_end(ap);
 
@@ -197,7 +197,7 @@ void Reporter::AnalyzerError(analyzer::Analyzer* a, const char* fmt,
 	va_start(ap, fmt);
 	// Always log to stderr.
 	// TODO: would be nice to also log a call stack.
-	DoLog("analyzer error", reporter_error, stderr, 0, 0, true, true, 0, fmt,
+	DoLog("analyzer error", reporter_error, stderr, nullptr, nullptr, true, true, nullptr, fmt,
 	      ap);
 	va_end(ap);
 	}
@@ -206,9 +206,9 @@ void Reporter::InternalWarning(const char* fmt, ...)
 	{
 	va_list ap;
 	va_start(ap, fmt);
-	FILE* out = EmitToStderr(warnings_to_stderr) ? stderr : 0;
+	FILE* out = EmitToStderr(warnings_to_stderr) ? stderr : nullptr;
 	// TODO: would be nice to also log a call stack.
-	DoLog("internal warning", reporter_warning, out, 0, 0, true, true, 0, fmt,
+	DoLog("internal warning", reporter_warning, out, nullptr, nullptr, true, true, nullptr, fmt,
 	      ap);
 	va_end(ap);
 	}
@@ -228,7 +228,7 @@ void Reporter::WeirdHelper(EventHandlerPtr event, val_list vl, const char* fmt_n
 	{
 	va_list ap;
 	va_start(ap, fmt_name);
-	DoLog("weird", event, 0, 0, &vl, false, false, 0, fmt_name, ap);
+	DoLog("weird", event, nullptr, nullptr, &vl, false, false, nullptr, fmt_name, ap);
 	va_end(ap);
 	}
 
@@ -382,7 +382,7 @@ void Reporter::DoLog(const char* prefix, EventHandlerPtr event, FILE* out,
 
 	int size = sizeof(tmp);
 	char* buffer  = tmp;
-	char* alloced = 0;
+	char* alloced = nullptr;
 
 	string loc_str;
 
diff --git a/src/Rule.cc b/src/Rule.cc
index ade2ca3f7c..3a7533b6f6 100644
--- a/src/Rule.cc
+++ b/src/Rule.cc
@@ -87,7 +87,7 @@ void Rule::AddRequires(const char* id, bool opposite_direction, bool negate)
 	{
 	Precond* p = new Precond;
 	p->id = copy_string(id);
-	p->rule = 0;
+	p->rule = nullptr;
 	p->opposite_dir = opposite_direction;
 	p->negate = negate;
 
diff --git a/src/Rule.h b/src/Rule.h
index 5d18ae8d84..29099dcb8e 100644
--- a/src/Rule.h
+++ b/src/Rule.h
@@ -25,7 +25,7 @@ public:
 		idx = rule_counter++;
 		location = arg_location;
 		active = true;
-		next = 0;
+		next = nullptr;
 		}
 
 	~Rule();
diff --git a/src/RuleMatcher.cc b/src/RuleMatcher.cc
index f492846a4d..0abafcb4da 100644
--- a/src/RuleMatcher.cc
+++ b/src/RuleMatcher.cc
@@ -48,10 +48,10 @@ RuleHdrTest::RuleHdrTest(Prot arg_prot, uint32_t arg_offset, uint32_t arg_size,
 	size = arg_size;
 	comp = arg_comp;
 	vals = arg_vals;
-	sibling = 0;
-	child = 0;
-	pattern_rules = 0;
-	pure_rules = 0;
+	sibling = nullptr;
+	child = nullptr;
+	pattern_rules = nullptr;
+	pure_rules = nullptr;
 	ruleset = new IntSet;
 	id = ++idcounter;
 	level = 0;
@@ -65,10 +65,10 @@ RuleHdrTest::RuleHdrTest(Prot arg_prot, Comp arg_comp, vector<IPPrefix> arg_v)
 	comp = arg_comp;
 	vals = new maskedvalue_list;
 	prefix_vals = std::move(arg_v);
-	sibling = 0;
-	child = 0;
-	pattern_rules = 0;
-	pure_rules = 0;
+	sibling = nullptr;
+	child = nullptr;
+	pattern_rules = nullptr;
+	pure_rules = nullptr;
 	ruleset = new IntSet;
 	id = ++idcounter;
 	level = 0;
@@ -103,7 +103,7 @@ RuleHdrTest::RuleHdrTest(RuleHdrTest& h)
 		for ( PatternSet* orig_set : h.psets[j] )
 			{
 			PatternSet* copied_set = new PatternSet;
-			copied_set->re = 0;
+			copied_set->re = nullptr;
 			copied_set->ids = orig_set->ids;
 			for ( const auto& pattern : orig_set->patterns )
 				copied_set->patterns.push_back(copy_string(pattern));
@@ -113,10 +113,10 @@ RuleHdrTest::RuleHdrTest(RuleHdrTest& h)
 			}
 		}
 
-	sibling = 0;
-	child = 0;
-	pattern_rules = 0;
-	pure_rules = 0;
+	sibling = nullptr;
+	child = nullptr;
+	pattern_rules = nullptr;
+	pure_rules = nullptr;
 	ruleset = new IntSet;
 	id = ++idcounter;
 	level = 0;
@@ -758,8 +758,8 @@ RuleEndpointState* RuleMatcher::InitEndpoint(analyzer::Analyzer* analyzer,
 		// Evaluate all rules on this node which don't contain
 		// any patterns.
 		for ( Rule* r = hdr_test->pure_rules; r; r = r->next )
-			if ( EvalRuleConditions(r, state, 0, 0, false) )
-				ExecRuleActions(r, state, 0, 0, false);
+			if ( EvalRuleConditions(r, state, nullptr, 0, false) )
+				ExecRuleActions(r, state, nullptr, 0, false);
 
 		// If we're on or above the RE_level, we may have some
 		// pattern matching to do.
@@ -989,7 +989,7 @@ void RuleMatcher::ExecPureRules(RuleEndpointState* state, bool eos)
 	for ( const auto& hdr_test : state->hdr_tests )
 		{
 		for ( Rule* r = hdr_test->pure_rules; r; r = r->next )
-			ExecRulePurely(r, 0, state, eos);
+			ExecRulePurely(r, nullptr, state, eos);
 		}
 	}
 
@@ -1001,14 +1001,14 @@ bool RuleMatcher::ExecRulePurely(Rule* r, BroString* s,
 
 	DBG_LOG(DBG_RULES, "Checking rule %s purely", r->ID());
 
-	if ( EvalRuleConditions(r, state, 0, 0, eos) )
+	if ( EvalRuleConditions(r, state, nullptr, 0, eos) )
 		{
 		DBG_LOG(DBG_RULES, "MATCH!");
 
 		if ( s )
 			ExecRuleActions(r, state, s->Bytes(), s->Len(), eos);
 		else
-			ExecRuleActions(r, state, 0, 0, eos);
+			ExecRuleActions(r, state, nullptr, 0, eos);
 
 		return true;
 		}
@@ -1098,7 +1098,7 @@ void RuleMatcher::ExecRule(Rule* rule, RuleEndpointState* state, bool eos)
 		for ( Rule* r = h->pure_rules; r; r = r->next )
 			if ( r == rule )
 				{ // found, so let's evaluate it
-				ExecRulePurely(rule, 0, state, eos);
+				ExecRulePurely(rule, nullptr, state, eos);
 				return;
 				}
 
@@ -1273,7 +1273,7 @@ static Val* get_bro_val(const char* label)
 	if ( ! id )
 		{
 		rules_error("unknown script-level identifier", label);
-		return 0;
+		return nullptr;
 		}
 
 	return id->ID_Val();
@@ -1464,7 +1464,7 @@ void RuleMatcherState::FinishEndpointMatcher()
 	delete orig_match_state;
 	delete resp_match_state;
 
-	orig_match_state = resp_match_state = 0;
+	orig_match_state = resp_match_state = nullptr;
 	}
 
 void RuleMatcherState::Match(Rule::PatternType type, const u_char* data,
diff --git a/src/RuleMatcher.h b/src/RuleMatcher.h
index 0650081000..4e4845cecf 100644
--- a/src/RuleMatcher.h
+++ b/src/RuleMatcher.h
@@ -67,7 +67,7 @@ typedef PList<BroString> bstr_list;
 
 // Get values from Bro's script-level variables.
 extern void id_to_maskedvallist(const char* id, maskedvalue_list* append_to,
-                                vector<IPPrefix>* prefix_vector = 0);
+                                vector<IPPrefix>* prefix_vector = nullptr);
 extern char* id_to_str(const char* id);
 extern uint32_t id_to_uint(const char* id);
 
@@ -256,7 +256,7 @@ public:
 	 * @return The results of the signature matching.
 	 */
 	MIME_Matches* Match(RuleFileMagicState* state, const u_char* data,
-	                   uint64_t len, MIME_Matches* matches = 0) const;
+	                   uint64_t len, MIME_Matches* matches = nullptr) const;
 
 
 	/**
@@ -313,7 +313,7 @@ public:
 	Val* BuildRuleStateValue(const Rule* rule,
 					const RuleEndpointState* state) const;
 
-	void GetStats(Stats* stats, RuleHdrTest* hdr_test = 0);
+	void GetStats(Stats* stats, RuleHdrTest* hdr_test = nullptr);
 	void DumpStats(BroFile* f);
 
 private:
@@ -373,13 +373,13 @@ private:
 // Keeps bi-directional matching-state.
 class RuleMatcherState {
 public:
-	RuleMatcherState()	{ orig_match_state = resp_match_state = 0; }
+	RuleMatcherState()	{ orig_match_state = resp_match_state = nullptr; }
 	~RuleMatcherState()
 		{ delete orig_match_state; delete resp_match_state; }
 
 	// ip may be nil.
 	void InitEndpointMatcher(analyzer::Analyzer* analyzer, const IP_Hdr* ip,
-				 int caplen, bool from_orig, analyzer::pia::PIA* pia = 0);
+				 int caplen, bool from_orig, analyzer::pia::PIA* pia = nullptr);
 
 	// bol/eol should be set to false for type Rule::PAYLOAD; they're
 	// deduced automatically.
diff --git a/src/Scope.cc b/src/Scope.cc
index c75dc64410..c324c6a134 100644
--- a/src/Scope.cc
+++ b/src/Scope.cc
@@ -20,7 +20,7 @@ Scope::Scope(IntrusivePtr<ID> id, attr_list* al)
 	: scope_id(std::move(id))
 	{
 	attrs = al;
-	return_type = 0;
+	return_type = nullptr;
 
 	inits = new id_list;
 
@@ -65,7 +65,7 @@ ID* Scope::GenerateTemporary(const char* name)
 id_list* Scope::GetInits()
 	{
 	id_list* ids = inits;
-	inits = 0;
+	inits = nullptr;
 	return ids;
 	}
 
@@ -76,9 +76,9 @@ void Scope::Describe(ODesc* d) const
 
 	else
 		{
-		d->Add(scope_id != 0);
+		d->Add(scope_id != nullptr);
 		d->SP();
-		d->Add(return_type != 0);
+		d->Add(return_type != nullptr);
 		d->SP();
 		d->Add(static_cast<uint64_t>(local.size()));
 		d->SP();
@@ -149,7 +149,7 @@ IntrusivePtr<ID> lookup_ID(const char* name, const char* curr_module,
 			return {NewRef{}, id};
 		}
 
-	return 0;
+	return nullptr;
 	}
 
 IntrusivePtr<ID> install_ID(const char* name, const char* module_name,
diff --git a/src/SerializationFormat.cc b/src/SerializationFormat.cc
index 1aa8346f3f..f2dd26bf5b 100644
--- a/src/SerializationFormat.cc
+++ b/src/SerializationFormat.cc
@@ -29,7 +29,7 @@ void SerializationFormat::StartRead(const char* data, uint32_t arg_len)
 
 void SerializationFormat::EndRead()
 	{
-	input = 0;
+	input = nullptr;
 	}
 
 void SerializationFormat::StartWrite()
@@ -37,7 +37,7 @@ void SerializationFormat::StartWrite()
 	if ( output && output_size > INITIAL_SIZE )
 		{
 		free(output);
-		output = 0;
+		output = nullptr;
 		}
 
 	if ( ! output )
@@ -54,7 +54,7 @@ uint32_t SerializationFormat::EndWrite(char** data)
 	{
 	uint32_t rval = output_pos;
 	*data = output;
-	output = 0;
+	output = nullptr;
 	output_size = 0;
 	output_pos = 0;
 	return rval;
@@ -193,7 +193,7 @@ bool BinarySerializationFormat::Read(char** str, int* len, const char* tag)
 	if ( ! ReadData(s, l) )
 		{
 		delete [] s;
-		*str = 0;
+		*str = nullptr;
 		return false;
 		}
 
diff --git a/src/Sessions.cc b/src/Sessions.cc
index ba40f08cad..104a39f28e 100644
--- a/src/Sessions.cc
+++ b/src/Sessions.cc
@@ -68,16 +68,16 @@ NetSessions::NetSessions()
 	if ( stp_correlate_pair )
 		stp_manager = new analyzer::stepping_stone::SteppingStoneManager();
 	else
-		stp_manager = 0;
+		stp_manager = nullptr;
 
 	discarder = new Discarder();
 	if ( ! discarder->IsActive() )
 		{
 		delete discarder;
-		discarder = 0;
+		discarder = nullptr;
 		}
 
-	packet_filter = 0;
+	packet_filter = nullptr;
 
 	dump_this_packet = false;
 	num_packets_processed = 0;
@@ -86,12 +86,12 @@ NetSessions::NetSessions()
 		pkt_profiler = new PacketProfiler(pkt_profile_mode,
 				pkt_profile_freq, pkt_profile_file->AsFile());
 	else
-		pkt_profiler = 0;
+		pkt_profiler = nullptr;
 
 	if ( arp_request || arp_reply || bad_arp )
 		arp_analyzer = new analyzer::arp::ARP_Analyzer();
 	else
-		arp_analyzer = 0;
+		arp_analyzer = nullptr;
 
 	memset(&stats, 0, sizeof(SessionStats));
 	}
@@ -153,7 +153,7 @@ void NetSessions::NextPacket(double t, const Packet* pkt)
 
 		const struct ip* ip = (const struct ip*) (pkt->data + pkt->hdr_size);
 		IP_Hdr ip_hdr(ip, false);
-		DoNextPacket(t, pkt, &ip_hdr, 0);
+		DoNextPacket(t, pkt, &ip_hdr, nullptr);
 		}
 
 	else if ( pkt->l3_proto == L3_IPV6 )
@@ -165,7 +165,7 @@ void NetSessions::NextPacket(double t, const Packet* pkt)
 			}
 
 		IP_Hdr ip_hdr((const struct ip6_hdr*) (pkt->data + pkt->hdr_size), false, caplen);
-		DoNextPacket(t, pkt, &ip_hdr, 0);
+		DoNextPacket(t, pkt, &ip_hdr, nullptr);
 		}
 
 	else if ( pkt->l3_proto == L3_ARP )
@@ -261,7 +261,7 @@ void NetSessions::DoNextPacket(double t, const Packet* pkt, const IP_Hdr* ip_hdr
 	if ( discarder && discarder->NextPacket(ip_hdr, len, caplen) )
 		return;
 
-	FragReassembler* f = 0;
+	FragReassembler* f = nullptr;
 
 	if ( ip_hdr->IsFragment() )
 		{
@@ -574,7 +574,7 @@ void NetSessions::DoNextPacket(double t, const Packet* pkt, const IP_Hdr* ip_hdr
 			return;
 			}
 
-		IP_Hdr* inner = 0;
+		IP_Hdr* inner = nullptr;
 
 		if ( gre_version != 0 )
 			{
@@ -662,7 +662,7 @@ void NetSessions::DoNextPacket(double t, const Packet* pkt, const IP_Hdr* ip_hdr
 		// We already know that connection.
 		if ( conn->IsReuse(t, data) )
 			{
-			conn->Event(connection_reused, 0);
+			conn->Event(connection_reused, nullptr);
 
 			Remove(conn);
 			conn = NewConn(key, t, &id, data, proto, ip_hdr->FlowLabel(), pkt, encapsulation);
@@ -686,16 +686,16 @@ void NetSessions::DoNextPacket(double t, const Packet* pkt, const IP_Hdr* ip_hdr
 
 	conn->CheckFlowLabel(is_orig, ip_hdr->FlowLabel());
 
-	Val* pkt_hdr_val = 0;
+	Val* pkt_hdr_val = nullptr;
 
 	if ( ipv6_ext_headers && ip_hdr->NumHeaders() > 1 )
 		{
 		pkt_hdr_val = ip_hdr->BuildPktHdrVal();
-		conn->Event(ipv6_ext_headers, 0, pkt_hdr_val);
+		conn->Event(ipv6_ext_headers, nullptr, pkt_hdr_val);
 		}
 
 	if ( new_packet )
-		conn->Event(new_packet, 0,
+		conn->Event(new_packet, nullptr,
 		        pkt_hdr_val ? pkt_hdr_val->Ref() : ip_hdr->BuildPktHdrVal());
 
 	conn->NextPacket(t, is_orig, ip_hdr, len, caplen, data,
@@ -739,7 +739,7 @@ void NetSessions::DoNextInnerPacket(double t, const Packet* pkt,
 		    ((network_time - (double)ts.tv_sec) * 1000000);
 		}
 
-	const u_char* data = 0;
+	const u_char* data = nullptr;
 
 	if ( inner->IP4_Hdr() )
 		data = (const u_char*) inner->IP4_Hdr();
@@ -906,7 +906,7 @@ Connection* NetSessions::FindConnection(Val* v)
 	{
 	BroType* vt = v->Type();
 	if ( ! IsRecord(vt->Tag()) )
-		return 0;
+		return nullptr;
 
 	RecordType* vr = vt->AsRecordType();
 	const val_list* vl = v->AsRecord();
@@ -931,7 +931,7 @@ Connection* NetSessions::FindConnection(Val* v)
 		resp_p = vr->FieldOffset("resp_p");
 
 		if ( orig_h < 0 || resp_h < 0 || orig_p < 0 || resp_p < 0 )
-			return 0;
+			return nullptr;
 
 		// ### we ought to check that the fields have the right
 		// types, too.
@@ -967,7 +967,7 @@ Connection* NetSessions::FindConnection(Val* v)
 		// This can happen due to pseudo-connections we
 		// construct, for example for packet headers embedded
 		// in ICMPs.
-		return 0;
+		return nullptr;
 		}
 
 	Connection* conn = nullptr;
@@ -1151,7 +1151,7 @@ Connection* NetSessions::NewConn(const ConnIDKey& k, double t, const ConnID* id,
 			break;
 		default:
 			reporter->InternalWarning("unknown transport protocol");
-			return 0;
+			return nullptr;
 	};
 
 	if ( tproto == TRANSPORT_TCP )
@@ -1163,7 +1163,7 @@ Connection* NetSessions::NewConn(const ConnIDKey& k, double t, const ConnID* id,
 	bool flip = false;
 
 	if ( ! WantConnection(src_h, dst_h, tproto, flags, flip) )
-		return 0;
+		return nullptr;
 
 	Connection* conn = new Connection(this, k, t, id, flow_label, pkt, encapsulation);
 	conn->SetTransport(tproto);
@@ -1175,11 +1175,11 @@ Connection* NetSessions::NewConn(const ConnIDKey& k, double t, const ConnID* id,
 		{
 		conn->Done();
 		Unref(conn);
-		return 0;
+		return nullptr;
 		}
 
 	if ( new_connection )
-		conn->Event(new_connection, 0);
+		conn->Event(new_connection, nullptr);
 
 	return conn;
 	}
diff --git a/src/Sessions.h b/src/Sessions.h
index efa4e430a2..8d67df1d96 100644
--- a/src/Sessions.h
+++ b/src/Sessions.h
@@ -75,9 +75,9 @@ public:
 	void GetStats(SessionStats& s) const;
 
 	void Weird(const char* name, const Packet* pkt,
-	    const EncapsulationStack* encap = 0, const char* addl = "");
+	    const EncapsulationStack* encap = nullptr, const char* addl = "");
 	void Weird(const char* name, const IP_Hdr* ip,
-	    const EncapsulationStack* encap = 0, const char* addl = "");
+	    const EncapsulationStack* encap = nullptr, const char* addl = "");
 
 	PacketFilter* GetPacketFilter()
 		{
diff --git a/src/SmithWaterman.cc b/src/SmithWaterman.cc
index 31611d1d4a..c9896d3c19 100644
--- a/src/SmithWaterman.cc
+++ b/src/SmithWaterman.cc
@@ -61,22 +61,22 @@ VectorVal* BroSubstring::VecToPolicy(Vec* vec)
 	RecordType* sw_substring_type =
 		internal_type("sw_substring")->AsRecordType();
 	if ( ! sw_substring_type )
-		return 0;
+		return nullptr;
 
 	RecordType* sw_align_type =
 		internal_type("sw_align")->AsRecordType();
 	if ( ! sw_align_type )
-		return 0;
+		return nullptr;
 
 	VectorType* sw_align_vec_type =
 		internal_type("sw_align_vec")->AsVectorType();
 	if ( ! sw_align_vec_type )
-		return 0;
+		return nullptr;
 
 	VectorVal* result =
 		new VectorVal(internal_type("sw_substring_vec")->AsVectorType());
 	if ( ! result )
-		return 0;
+		return nullptr;
 
 	if ( vec )
 		{
@@ -235,9 +235,9 @@ public:
 		{
 		// Make sure access is in allowed range.
 		if ( row < 0 || row >= _rows )
-			return 0;
+			return nullptr;
 		if ( col < 0 || col >= _cols )
-			return 0;
+			return nullptr;
 
 		return &(_nodes[row * _cols + col]);
 		}
@@ -359,7 +359,7 @@ static void sw_collect_multiple(BroSubstring::Vec* result,
 				{
 				BroSubstring::Vec* old_al = *it;
 
-				if ( old_al == 0 )
+				if ( old_al == nullptr )
 					continue;
 
 				for ( BroSubstring::VecIt it2 = old_al->begin();
@@ -372,7 +372,7 @@ static void sw_collect_multiple(BroSubstring::Vec* result,
 							{
 							delete_each(new_al);
 							delete new_al;
-							new_al = 0;
+							new_al = nullptr;
 							goto end_loop;
 							}
 
@@ -398,7 +398,7 @@ end_loop:
 		{
 		BroSubstring::Vec* al = *it;
 
-		if ( al == 0 )
+		if ( al == nullptr )
 			continue;
 
 		for ( BroSubstring::VecIt it2 = al->begin();
@@ -432,8 +432,8 @@ BroSubstring::Vec* smith_waterman(const BroString* s1, const BroString* s2,
 	byte_vec string2 = s2->Bytes();
 
 	SWNodeMatrix matrix(s1, s2);	// dynamic programming matrix.
-	SWNode* node_max = 0;	// pointer to the best score's node
-	SWNode* node_br_max = 0;	// pointer to lowest-right matching node
+	SWNode* node_max = nullptr;	// pointer to the best score's node
+	SWNode* node_br_max = nullptr;	// pointer to lowest-right matching node
 
 	// The highest score in the matrix, globally.  We initialize to 1
 	// because we are only interested in real scores (initializing to
diff --git a/src/Stats.cc b/src/Stats.cc
index 8720933fae..8ab8a21cbc 100644
--- a/src/Stats.cc
+++ b/src/Stats.cc
@@ -339,7 +339,7 @@ void ProfileLogger::SegmentProfile(const char* name, const Location* loc,
 
 SampleLogger::SampleLogger()
 	{
-	static TableType* load_sample_info = 0;
+	static TableType* load_sample_info = nullptr;
 
 	if ( ! load_sample_info )
 		load_sample_info = internal_type("load_sample_info")->AsTableType();
@@ -355,14 +355,14 @@ SampleLogger::~SampleLogger()
 void SampleLogger::FunctionSeen(const Func* func)
 	{
 	Val* idx = new StringVal(func->Name());
-	load_samples->Assign(idx, 0);
+	load_samples->Assign(idx, nullptr);
 	Unref(idx);
 	}
 
 void SampleLogger::LocationSeen(const Location* loc)
 	{
 	Val* idx = new StringVal(loc->filename);
-	load_samples->Assign(idx, 0);
+	load_samples->Assign(idx, nullptr);
 	Unref(idx);
 	}
 
@@ -438,7 +438,7 @@ void PacketProfiler::ProfilePkt(double t, unsigned int bytes)
 		getrusage(RUSAGE_SELF, &res);
 		gettimeofday(&ptimestamp, 0);
 
-		get_memory_usage(&last_mem, 0);
+		get_memory_usage(&last_mem, nullptr);
 		last_Utime = res.ru_utime.tv_sec + res.ru_utime.tv_usec / 1e6;
 		last_Stime = res.ru_stime.tv_sec + res.ru_stime.tv_usec / 1e6;
 		last_Rtime = ptimestamp.tv_sec + ptimestamp.tv_usec / 1e6;
@@ -462,7 +462,7 @@ void PacketProfiler::ProfilePkt(double t, unsigned int bytes)
 			ptimestamp.tv_sec + ptimestamp.tv_usec / 1e6;
 
 		uint64_t curr_mem;
-		get_memory_usage(&curr_mem, 0);
+		get_memory_usage(&curr_mem, nullptr);
 
 		file->Write(fmt("%.06f %.03f %" PRIu64 " %" PRIu64 " %.03f %.03f %.03f %" PRIu64 "\n",
 				t, time-last_timestamp, pkt_cnt, byte_cnt,
diff --git a/src/Stmt.cc b/src/Stmt.cc
index 0a7e0cdcae..5b2a7023ba 100644
--- a/src/Stmt.cc
+++ b/src/Stmt.cc
@@ -182,7 +182,7 @@ TraversalCode ExprListStmt::Traverse(TraversalCallback* cb) const
 	HANDLE_TC_STMT_POST(tc);
 	}
 
-static BroFile* print_stdout = 0;
+static BroFile* print_stdout = nullptr;
 
 static IntrusivePtr<EnumVal> lookup_enum_val(const char* module_name, const char* name)
 	{
@@ -629,7 +629,7 @@ SwitchStmt::SwitchStmt(IntrusivePtr<Expr> index, case_list* arg_cases)
 						NegExpr* ne = (NegExpr*)(expr);
 
 						if ( ne->Op()->IsConst() )
-							Unref(exprs.replace(j, new ConstExpr(ne->Eval(0))));
+							Unref(exprs.replace(j, new ConstExpr(ne->Eval(nullptr))));
 						}
 						break;
 
@@ -638,7 +638,7 @@ SwitchStmt::SwitchStmt(IntrusivePtr<Expr> index, case_list* arg_cases)
 						PosExpr* pe = (PosExpr*)(expr);
 
 						if ( pe->Op()->IsConst() )
-							Unref(exprs.replace(j, new ConstExpr(pe->Eval(0))));
+							Unref(exprs.replace(j, new ConstExpr(pe->Eval(nullptr))));
 						}
 						break;
 
@@ -648,7 +648,7 @@ SwitchStmt::SwitchStmt(IntrusivePtr<Expr> index, case_list* arg_cases)
 
 						if ( ne->Id()->IsConst() )
 							{
-							auto v = ne->Eval(0);
+							auto v = ne->Eval(nullptr);
 
 							if ( v )
 								Unref(exprs.replace(j, new ConstExpr(std::move(v))));
@@ -757,7 +757,7 @@ bool SwitchStmt::AddCaseLabelTypeMapping(ID* t, int idx)
 std::pair<int, ID*> SwitchStmt::FindCaseLabelMatch(const Val* v) const
 	{
 	int label_idx = -1;
-	ID* label_id = 0;
+	ID* label_id = nullptr;
 
 	// Find matching expression cases.
 	if ( case_label_value_map.Length() )
@@ -1065,7 +1065,7 @@ ForStmt::ForStmt(id_list* arg_loop_vars, IntrusivePtr<Expr> loop_expr)
 	: ExprStmt(STMT_FOR, std::move(loop_expr))
 	{
 	loop_vars = arg_loop_vars;
-	body = 0;
+	body = nullptr;
 
 	if ( e->Type()->Tag() == TYPE_TABLE )
 		{
@@ -1090,7 +1090,7 @@ ForStmt::ForStmt(id_list* arg_loop_vars, IntrusivePtr<Expr> loop_expr)
 				{
 				add_local({NewRef{}, (*loop_vars)[i]},
 						{NewRef{}, ind_type}, INIT_NONE,
-						0, 0, VAR_REGULAR);
+						nullptr, nullptr, VAR_REGULAR);
 				}
 			}
 		}
@@ -1106,7 +1106,7 @@ ForStmt::ForStmt(id_list* arg_loop_vars, IntrusivePtr<Expr> loop_expr)
 		BroType* t = (*loop_vars)[0]->Type();
 		if ( ! t )
 			add_local({NewRef{}, (*loop_vars)[0]}, base_type(TYPE_COUNT),
-						INIT_NONE, 0, 0, VAR_REGULAR);
+						INIT_NONE, nullptr, nullptr, VAR_REGULAR);
 
 		else if ( ! IsIntegral(t->Tag()) )
 			{
@@ -1127,7 +1127,7 @@ ForStmt::ForStmt(id_list* arg_loop_vars, IntrusivePtr<Expr> loop_expr)
 		if ( ! t )
 			add_local({NewRef{}, (*loop_vars)[0]},
 					base_type(TYPE_STRING),
-					INIT_NONE, 0, 0, VAR_REGULAR);
+					INIT_NONE, nullptr, nullptr, VAR_REGULAR);
 
 		else if ( t->Tag() != TYPE_STRING )
 			{
@@ -1158,7 +1158,7 @@ ForStmt::ForStmt(id_list* arg_loop_vars,
 		else
 			{
 			add_local(value_var, {NewRef{}, yield_type}, INIT_NONE,
-			                 0, 0, VAR_REGULAR);
+			                 nullptr, nullptr, VAR_REGULAR);
 			}
 		}
 	else
@@ -1471,7 +1471,7 @@ void ReturnStmt::Describe(ODesc* d) const
 	{
 	Stmt::Describe(d);
 	if ( ! d->IsReadable() )
-		d->Add(e != 0);
+		d->Add(e != nullptr);
 
 	if ( e )
 		{
@@ -1600,7 +1600,7 @@ IntrusivePtr<Val> EventBodyList::Exec(Frame* f, stmt_flow_type& flow) const
 
 	// Simulate a return so the hooks operate properly.
 	stmt_flow_type ft = FLOW_RETURN;
-	(void) post_execute_stmt(f->GetNextStmt(), f, 0, &ft);
+	(void) post_execute_stmt(f->GetNextStmt(), f, nullptr, &ft);
 
 	return nullptr;
 	}
@@ -1656,7 +1656,7 @@ IntrusivePtr<Val> InitStmt::Exec(Frame* f, stmt_flow_type& flow) const
 		{
 		BroType* t = aggr->Type();
 
-		Val* v = 0;
+		Val* v = nullptr;
 
 		switch ( t->Tag() ) {
 		case TYPE_RECORD:
diff --git a/src/Tag.cc b/src/Tag.cc
index f09b06c054..e0145afd6d 100644
--- a/src/Tag.cc
+++ b/src/Tag.cc
@@ -41,13 +41,13 @@ Tag::Tag()
 	{
 	type = 0;
 	subtype = 0;
-	val = 0;
+	val = nullptr;
 	}
 
 Tag::~Tag()
 	{
 	Unref(val);
-	val = 0;
+	val = nullptr;
 	}
 
 Tag& Tag::operator=(const Tag& other)
diff --git a/src/Traverse.h b/src/Traverse.h
index 2ef672ddd7..2e528905e0 100644
--- a/src/Traverse.h
+++ b/src/Traverse.h
@@ -12,7 +12,7 @@ class ID;
 
 class TraversalCallback {
 public:
-	TraversalCallback()	{ current_scope = 0; }
+	TraversalCallback()	{ current_scope = nullptr; }
 	virtual ~TraversalCallback() {}
 
 	virtual TraversalCode PreFunction(const Func*) { return TC_CONTINUE; }
diff --git a/src/Trigger.cc b/src/Trigger.cc
index d3b11e5cd8..773ae78c23 100644
--- a/src/Trigger.cc
+++ b/src/Trigger.cc
@@ -130,10 +130,10 @@ Trigger::Trigger(Expr* arg_cond, Stmt* arg_body, Stmt* arg_timeout_stmts,
 	timeout_stmts = arg_timeout_stmts;
 	timeout = arg_timeout;
 	frame = arg_frame->Clone();
-	timer = 0;
+	timer = nullptr;
 	delayed = false;
 	disabled = false;
-	attached = 0;
+	attached = nullptr;
 	is_return = arg_is_return;
 	location = arg_location;
 	timeout_value = -1;
diff --git a/src/TunnelEncapsulation.h b/src/TunnelEncapsulation.h
index 4f18b6118b..9dbf169326 100644
--- a/src/TunnelEncapsulation.h
+++ b/src/TunnelEncapsulation.h
@@ -129,7 +129,7 @@ protected:
  */
 class EncapsulationStack {
 public:
-	EncapsulationStack() : conns(0)
+	EncapsulationStack() : conns(nullptr)
 		{}
 
 	EncapsulationStack(const EncapsulationStack& other)
@@ -137,7 +137,7 @@ public:
 		if ( other.conns )
 			conns = new vector<EncapsulatingConn>(*(other.conns));
 		else
-			conns = 0;
+			conns = nullptr;
 		}
 
 	EncapsulationStack& operator=(const EncapsulationStack& other)
@@ -150,7 +150,7 @@ public:
 		if ( other.conns )
 			conns = new vector<EncapsulatingConn>(*(other.conns));
 		else
-			conns = 0;
+			conns = nullptr;
 
 		return *this;
 		}
diff --git a/src/Type.cc b/src/Type.cc
index baa1b6552a..a55781c648 100644
--- a/src/Type.cc
+++ b/src/Type.cc
@@ -541,7 +541,7 @@ void FuncType::Describe(ODesc* d) const
 		{
 		d->Add(int(Tag()));
 		d->Add(flavor);
-		d->Add(yield != 0);
+		d->Add(yield != nullptr);
 		args->DescribeFields(d);
 		if ( yield )
 			yield->Describe(d);
@@ -648,7 +648,7 @@ bool RecordType::HasField(const char* field) const
 BroType* RecordType::FieldType(const char* field) const
 	{
 	int offset = FieldOffset(field);
-	return offset >= 0 ? FieldType(offset) : 0;
+	return offset >= 0 ? FieldType(offset) : nullptr;
 	}
 
 BroType* RecordType::FieldType(int field) const
@@ -783,7 +783,7 @@ IntrusivePtr<TableVal> RecordType::GetRecordFieldsVal(const RecordVal* rv) const
 		if ( fv )
 			::Ref(fv);
 
-		bool logged = (fd->attrs && fd->FindAttr(ATTR_LOG) != 0);
+		bool logged = (fd->attrs && fd->FindAttr(ATTR_LOG) != nullptr);
 
 		auto nr = make_intrusive<RecordVal>(internal_type("record_field")->AsRecordType());
 
@@ -1575,10 +1575,10 @@ bool same_type(const BroType* t1, const BroType* t2, bool is_init, bool match_re
 bool same_attrs(const Attributes* a1, const Attributes* a2)
 	{
 	if ( ! a1 )
-		return (a2 == 0);
+		return (a2 == nullptr);
 
 	if ( ! a2 )
-		return (a1 == 0);
+		return (a1 == nullptr);
 
 	return (*a1 == *a2);
 	}
@@ -2023,7 +2023,7 @@ IntrusivePtr<BroType> init_type(Expr* init)
 	// Could be a record, a set, or a list of table elements.
 	Expr* e0 = el[0];
 
-	if ( e0->IsRecordElement(0) )
+	if ( e0->IsRecordElement(nullptr) )
 		// ListExpr's know how to build a record from their
 		// components.
 		return init_list->InitType();
@@ -2039,7 +2039,7 @@ IntrusivePtr<BroType> init_type(Expr* init)
 	for ( int i = 1; t && i < el.length(); ++i )
 		{
 		auto el_t = el[i]->InitType();
-		BroType* ti = el_t ? reduce_type(el_t.get()) : 0;
+		BroType* ti = el_t ? reduce_type(el_t.get()) : nullptr;
 
 		if ( ! ti )
 			return nullptr;
diff --git a/src/Type.h b/src/Type.h
index 9686bcdf9f..a201c8ce3c 100644
--- a/src/Type.h
+++ b/src/Type.h
@@ -304,12 +304,12 @@ public:
 
 	bool IsSet() const
 		{
-		return tag == TYPE_TABLE && (YieldType() == 0);
+		return tag == TYPE_TABLE && (YieldType() == nullptr);
 		}
 
 	bool IsTable() const
 		{
-		return tag == TYPE_TABLE && (YieldType() != 0);
+		return tag == TYPE_TABLE && (YieldType() != nullptr);
 		}
 
 	BroType* Ref()		{ ::Ref(this); return this; }
@@ -357,7 +357,7 @@ public:
 	const type_list* Types() const	{ return &types; }
 	type_list* Types()		{ return &types; }
 
-	bool IsPure() const		{ return pure_type != 0; }
+	bool IsPure() const		{ return pure_type != nullptr; }
 
 	// Returns the underlying pure type, or nil if the list
 	// is not pure or is empty.
@@ -485,12 +485,12 @@ protected:
 
 class TypeDecl final {
 public:
-	TypeDecl(IntrusivePtr<BroType> t, const char* i, attr_list* attrs = 0, bool in_record = false);
+	TypeDecl(IntrusivePtr<BroType> t, const char* i, attr_list* attrs = nullptr, bool in_record = false);
 	TypeDecl(const TypeDecl& other);
 	~TypeDecl();
 
 	const Attr* FindAttr(attr_tag a) const
-		{ return attrs ? attrs->FindAttr(a) : 0; }
+		{ return attrs ? attrs->FindAttr(a) : nullptr; }
 
 	void DescribeReST(ODesc* d, bool roles_only = false) const;
 
@@ -547,19 +547,19 @@ public:
 	bool IsFieldDeprecated(int field) const
 		{
 		const TypeDecl* decl = FieldDecl(field);
-		return decl && decl->FindAttr(ATTR_DEPRECATED) != 0;
+		return decl && decl->FindAttr(ATTR_DEPRECATED) != nullptr;
 		}
 
 	bool FieldHasAttr(int field, attr_tag at) const
 		{
 		const TypeDecl* decl = FieldDecl(field);
-		return decl && decl->FindAttr(at) != 0;
+		return decl && decl->FindAttr(at) != nullptr;
 		}
 
 	std::string GetFieldDeprecationWarning(int field, bool has_check) const;
 
 protected:
-	RecordType() { types = 0; }
+	RecordType() { types = nullptr; }
 
 	int num_fields;
 	type_decl_list* types;
diff --git a/src/UID.h b/src/UID.h
index 711541e283..68a87758e8 100644
--- a/src/UID.h
+++ b/src/UID.h
@@ -28,7 +28,7 @@ public:
 	 * Construct a UID of a given bit-length, optionally from given values.
 	 * @see UID::Set
 	 */
-	explicit UID(bro_uint_t bits, const uint64_t* v = 0, size_t n = 0)
+	explicit UID(bro_uint_t bits, const uint64_t* v = nullptr, size_t n = 0)
 		{ Set(bits, v, n); }
 
 	/**
@@ -47,7 +47,7 @@ public:
 	 *          64, then a value is truncated to bit in desired bit-length.
 	 * @param n number of 64-bit elements in array pointed to by \a v.
 	 */
-	void Set(bro_uint_t bits, const uint64_t* v = 0, size_t n = 0);
+	void Set(bro_uint_t bits, const uint64_t* v = nullptr, size_t n = 0);
 
 	/**
 	 * Returns a base62 (characters 0-9, A-Z, a-z) representation of the UID.
diff --git a/src/Val.cc b/src/Val.cc
index 0597323b89..580ff4d58c 100644
--- a/src/Val.cc
+++ b/src/Val.cc
@@ -48,7 +48,7 @@ Val::Val(Func* f)
 
 static FileType* GetStringFileType() noexcept
 	{
-	static FileType* string_file_type = 0;
+	static FileType* string_file_type = nullptr;
 	if ( ! string_file_type )
 		string_file_type = new FileType(base_type(TYPE_STRING));
 	return string_file_type;
@@ -366,13 +366,13 @@ void Val::ValDescribeReST(ODesc* d) const
 #ifdef DEBUG
 ID* Val::GetID() const
 	{
-	return bound_id ? global_scope()->Lookup(bound_id) : 0;
+	return bound_id ? global_scope()->Lookup(bound_id) : nullptr;
 	}
 
 void Val::SetID(ID* id)
 	{
 	delete [] bound_id;
-	bound_id = id ? copy_string(id->Name()) : 0;
+	bound_id = id ? copy_string(id->Name()) : nullptr;
 	}
 #endif
 
@@ -1233,7 +1233,7 @@ TableVal* ListVal::ConvertToSet() const
 	TableVal* t = new TableVal(std::move(s));
 
 	for ( const auto& val : vals )
-		t->Assign(val, 0);
+		t->Assign(val, nullptr);
 
 	return t;
 	}
@@ -1381,16 +1381,16 @@ TableVal::TableVal(IntrusivePtr<TableType> t, IntrusivePtr<Attributes> a) : Val(
 void TableVal::Init(IntrusivePtr<TableType> t)
 	{
 	table_type = std::move(t);
-	expire_func = 0;
-	expire_time = 0;
-	expire_cookie = 0;
-	timer = 0;
-	def_val = 0;
+	expire_func = nullptr;
+	expire_time = nullptr;
+	expire_cookie = nullptr;
+	timer = nullptr;
+	def_val = nullptr;
 
 	if ( table_type->IsSubNetIndex() )
 		subnets = new PrefixTable;
 	else
-		subnets = 0;
+		subnets = nullptr;
 
 	table_hash = new CompositeHash(IntrusivePtr<TypeList>(NewRef{},
 	                               table_type->Indices()));
@@ -1603,12 +1603,12 @@ bool TableVal::AddTo(Val* val, bool is_first_init, bool propagate_ops) const
 
 		if ( type->IsSet() )
 			{
-			if ( ! t->Assign(v->Value(), k, 0) )
+			if ( ! t->Assign(v->Value(), k, nullptr) )
 				 return false;
 			}
 		else
 			{
-			if ( ! t->Assign(0, k, {NewRef{}, v->Value()}) )
+			if ( ! t->Assign(nullptr, k, {NewRef{}, v->Value()}) )
 				 return false;
 			}
 		}
@@ -1804,11 +1804,11 @@ IntrusivePtr<Val> TableVal::Default(Val* index)
 			auto coerce = make_intrusive<RecordCoerceExpr>(
 			        IntrusivePtr{NewRef{}, def_attr->AttrExpr()},
 			        IntrusivePtr{NewRef{}, ytype->AsRecordType()});
-			def_val = coerce->Eval(0);
+			def_val = coerce->Eval(nullptr);
 			}
 
 		else
-			def_val = def_attr->AttrExpr()->Eval(0);
+			def_val = def_attr->AttrExpr()->Eval(nullptr);
 		}
 
 	if ( ! def_val )
@@ -1942,7 +1942,7 @@ IntrusivePtr<TableVal> TableVal::LookupSubnetValues(const SubNetVal* search)
 		if ( entry && entry->Value() )
 			nt->Assign(s, {NewRef{}, entry->Value()});
 		else
-			nt->Assign(s, 0); // set
+			nt->Assign(s, nullptr); // set
 
 		if ( entry )
 			{
@@ -2050,7 +2050,7 @@ void TableVal::CallChangeFunc(const Val* index, Val* old_value, OnChangeType tpe
 IntrusivePtr<Val> TableVal::Delete(const Val* index)
 	{
 	HashKey* k = ComputeHash(index);
-	TableEntryVal* v = k ? AsNonConstTable()->RemoveEntry(k) : 0;
+	TableEntryVal* v = k ? AsNonConstTable()->RemoveEntry(k) : nullptr;
 	IntrusivePtr<Val> va{NewRef{}, v ? (v->Value() ? v->Value() : this) : nullptr};
 
 	if ( subnets && ! subnets->Remove(index) )
@@ -2128,7 +2128,7 @@ ListVal* TableVal::ConvertToPureList() const
 	if ( tl->length() != 1 )
 		{
 		InternalWarning("bad index type in TableVal::ConvertToPureList");
-		return 0;
+		return nullptr;
 		}
 
 	return ConvertToList((*tl)[0]->Tag());
@@ -2136,7 +2136,7 @@ ListVal* TableVal::ConvertToPureList() const
 
 Attr* TableVal::FindAttr(attr_tag t) const
 	{
-	return attrs ? attrs->FindAttr(t) : 0;
+	return attrs ? attrs->FindAttr(t) : nullptr;
 	}
 
 void TableVal::Describe(ODesc* d) const
@@ -2253,7 +2253,7 @@ bool TableVal::ExpandCompoundAndInit(val_list* vl, int k, IntrusivePtr<Val> new_
 
 bool TableVal::CheckAndAssign(Val* index, IntrusivePtr<Val> new_val)
 	{
-	Val* v = 0;
+	Val* v = nullptr;
 	if ( subnets )
 		// We need an exact match here.
 		v = (Val*) subnets->Lookup(index, true);
@@ -2392,7 +2392,7 @@ void TableVal::DoExpire(double t)
 
 	if ( ! v )
 		{
-		expire_cookie = 0;
+		expire_cookie = nullptr;
 		InitTimer(table_expire_interval);
 		}
 	else
@@ -2419,7 +2419,7 @@ double TableVal::GetExpireTime()
 	if ( interval >= 0 )
 		return interval;
 
-	expire_time = 0;
+	expire_time = nullptr;
 
 	if ( timer )
 		timer_mgr->Cancel(timer);
@@ -2819,7 +2819,7 @@ IntrusivePtr<RecordVal> RecordVal::CoerceTo(RecordType* t, bool allow_orphaning)
 	if ( same_type(Type(), t) )
 		return {NewRef{}, this};
 
-	return CoerceTo(t, 0, allow_orphaning);
+	return CoerceTo(t, nullptr, allow_orphaning);
 	}
 
 IntrusivePtr<TableVal> RecordVal::GetRecordFieldsVal() const
@@ -2975,7 +2975,7 @@ bool VectorVal::Assign(unsigned int index, IntrusivePtr<Val> element)
 	     ! same_type(element->Type(), vector_type->YieldType(), false) )
 		return false;
 
-	Val* val_at_index = 0;
+	Val* val_at_index = nullptr;
 
 	if ( index < val.vector_val->size() )
 		val_at_index = (*val.vector_val)[index];
diff --git a/src/Val.h b/src/Val.h
index 96b610892d..80bce5cb69 100644
--- a/src/Val.h
+++ b/src/Val.h
@@ -310,7 +310,7 @@ public:
 
 	// To be overridden by mutable derived class to enable change
 	// notification.
-	virtual notifier::Modifiable* Modifiable()	{ return 0; }
+	virtual notifier::Modifiable* Modifiable()	{ return nullptr; }
 
 #ifdef DEBUG
 	// For debugging, we keep a reference to the global ID to which a
@@ -804,7 +804,7 @@ public:
 	void ClearTimer(Timer* t)
 		{
 		if ( timer == t )
-			timer = 0;
+			timer = nullptr;
 		}
 
 	HashKey* ComputeHash(const Val* index) const;
@@ -843,7 +843,7 @@ protected:
 	IntrusivePtr<Val> Default(Val* index);
 
 	// Returns true if item expiration is enabled.
-	bool ExpirationEnabled()	{ return expire_time != 0; }
+	bool ExpirationEnabled()	{ return expire_time != nullptr; }
 
 	// Returns the expiration time defined by %{create,read,write}_expire
 	// attribute, or -1 for unset/invalid values. In the invalid case, an
diff --git a/src/Var.cc b/src/Var.cc
index 406e8ab54b..ac1a0647fb 100644
--- a/src/Var.cc
+++ b/src/Var.cc
@@ -216,7 +216,7 @@ static void make_var(ID* id, IntrusivePtr<BroType> t, init_class c,
 		// For events, add a function value (without any body) here so that
 		// we can later access the ID even if no implementations have been
 		// defined.
-		Func* f = new BroFunc(id, 0, 0, 0, 0);
+		Func* f = new BroFunc(id, nullptr, nullptr, 0, 0);
 		id->SetVal(make_intrusive<Val>(f));
 		}
 	}
@@ -305,7 +305,7 @@ static void transfer_arg_defaults(RecordType* args, RecordType* recv)
 		TypeDecl* args_i = args->FieldDecl(i);
 		TypeDecl* recv_i = recv->FieldDecl(i);
 
-		Attr* def = args_i->attrs ? args_i->attrs->FindAttr(ATTR_DEFAULT) : 0;
+		Attr* def = args_i->attrs ? args_i->attrs->FindAttr(ATTR_DEFAULT) : nullptr;
 
 		if ( ! def )
 			continue;
@@ -379,7 +379,7 @@ void begin_func(ID* id, const char* module_name, function_flavor flavor,
 		case FUNC_FLAVOR_HOOK:
 			if ( is_redef )
 				// Clear out value so it will be replaced.
-				id->SetVal(0);
+				id->SetVal(nullptr);
 			break;
 
 		case FUNC_FLAVOR_FUNCTION:
diff --git a/src/broker/Manager.cc b/src/broker/Manager.cc
index 79864ae86c..8c72ca7cc6 100644
--- a/src/broker/Manager.cc
+++ b/src/broker/Manager.cc
@@ -695,7 +695,7 @@ RecordVal* Manager::MakeEvent(val_list* args, Frame* frame)
 	auto rval = new RecordVal(BifType::Record::Broker::Event);
 	auto arg_vec = new VectorVal(vector_of_data_type);
 	rval->Assign(1, arg_vec);
-	Func* func = 0;
+	Func* func = nullptr;
 	scoped_reporter_location srl{frame};
 
 	for ( auto i = 0; i < args->length(); ++i )
@@ -738,7 +738,7 @@ RecordVal* Manager::MakeEvent(val_list* args, Frame* frame)
 
 		if ( ! same_type(got_type, expected_type) )
 			{
-			rval->Assign(0, 0);
+			rval->Assign(0, nullptr);
 			Error("event parameter #%d type mismatch, got %s, expect %s", i,
 			      type_name(got_type->Tag()),
 			      type_name(expected_type->Tag()));
@@ -758,7 +758,7 @@ RecordVal* Manager::MakeEvent(val_list* args, Frame* frame)
 		if ( ! data_val->Lookup(0) )
 			{
 			Unref(data_val);
-			rval->Assign(0, 0);
+			rval->Assign(0, nullptr);
 			Error("failed to convert param #%d of type %s to broker data",
 				  i, type_name(got_type->Tag()));
 			return rval;
diff --git a/src/main.cc b/src/main.cc
index acb0beb6e7..b44543173a 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -84,44 +84,44 @@ int perftools_profile = 0;
 
 DNS_Mgr* dns_mgr;
 TimerMgr* timer_mgr;
-ValManager* val_mgr = 0;
-logging::Manager* log_mgr = 0;
-threading::Manager* thread_mgr = 0;
-input::Manager* input_mgr = 0;
-plugin::Manager* plugin_mgr = 0;
-analyzer::Manager* analyzer_mgr = 0;
-file_analysis::Manager* file_mgr = 0;
-zeekygen::Manager* zeekygen_mgr = 0;
-iosource::Manager* iosource_mgr = 0;
-bro_broker::Manager* broker_mgr = 0;
-zeek::Supervisor* zeek::supervisor_mgr = 0;
-trigger::Manager* trigger_mgr = 0;
+ValManager* val_mgr = nullptr;
+logging::Manager* log_mgr = nullptr;
+threading::Manager* thread_mgr = nullptr;
+input::Manager* input_mgr = nullptr;
+plugin::Manager* plugin_mgr = nullptr;
+analyzer::Manager* analyzer_mgr = nullptr;
+file_analysis::Manager* file_mgr = nullptr;
+zeekygen::Manager* zeekygen_mgr = nullptr;
+iosource::Manager* iosource_mgr = nullptr;
+bro_broker::Manager* broker_mgr = nullptr;
+zeek::Supervisor* zeek::supervisor_mgr = nullptr;
+trigger::Manager* trigger_mgr = nullptr;
 
 std::vector<std::string> zeek_script_prefixes;
 Stmt* stmts;
-EventHandlerPtr net_done = 0;
-RuleMatcher* rule_matcher = 0;
-EventRegistry* event_registry = 0;
-ProfileLogger* profiling_logger = 0;
-ProfileLogger* segment_logger = 0;
-SampleLogger* sample_logger = 0;
+EventHandlerPtr net_done = nullptr;
+RuleMatcher* rule_matcher = nullptr;
+EventRegistry* event_registry = nullptr;
+ProfileLogger* profiling_logger = nullptr;
+ProfileLogger* segment_logger = nullptr;
+SampleLogger* sample_logger = nullptr;
 int signal_val = 0;
 extern char version[];
-const char* command_line_policy = 0;
+const char* command_line_policy = nullptr;
 vector<string> params;
 set<string> requested_plugins;
-const char* proc_status_file = 0;
+const char* proc_status_file = nullptr;
 
-OpaqueType* md5_type = 0;
-OpaqueType* sha1_type = 0;
-OpaqueType* sha256_type = 0;
-OpaqueType* entropy_type = 0;
-OpaqueType* cardinality_type = 0;
-OpaqueType* topk_type = 0;
-OpaqueType* bloomfilter_type = 0;
-OpaqueType* x509_opaque_type = 0;
-OpaqueType* ocsp_resp_opaque_type = 0;
-OpaqueType* paraglob_type = 0;
+OpaqueType* md5_type = nullptr;
+OpaqueType* sha1_type = nullptr;
+OpaqueType* sha256_type = nullptr;
+OpaqueType* entropy_type = nullptr;
+OpaqueType* cardinality_type = nullptr;
+OpaqueType* topk_type = nullptr;
+OpaqueType* bloomfilter_type = nullptr;
+OpaqueType* x509_opaque_type = nullptr;
+OpaqueType* ocsp_resp_opaque_type = nullptr;
+OpaqueType* paraglob_type = nullptr;
 
 // Keep copy of command line
 int bro_argc;
@@ -130,7 +130,7 @@ char** bro_argv;
 const char* zeek_version()
 	{
 #ifdef DEBUG
-	static char* debug_version = 0;
+	static char* debug_version = nullptr;
 
 	if ( ! debug_version )
 		{
@@ -311,7 +311,7 @@ void terminate_bro()
 	// free the global scope
 	pop_scope();
 
-	reporter = 0;
+	reporter = nullptr;
 	}
 
 void zeek_terminate_loop(const char* reason)
@@ -527,8 +527,8 @@ int main(int argc, char** argv)
 	if ( options.random_seed_input_file )
 		seed_load_file = options.random_seed_input_file->data();
 
-	init_random_seed((seed_load_file && *seed_load_file ? seed_load_file : 0),
-					 options.random_seed_output_file ? options.random_seed_output_file->data() : 0);
+	init_random_seed((seed_load_file && *seed_load_file ? seed_load_file : nullptr),
+					 options.random_seed_output_file ? options.random_seed_output_file->data() : nullptr);
 	// DEBUG_MSG("HMAC key: %s\n", md5_digest_print(shared_hmac_md5_key));
 	init_hash_function();
 
@@ -748,7 +748,7 @@ int main(int argc, char** argv)
 
 	if ( g_policy_debug )
 		// ### Add support for debug command file.
-		dbg_init_debugger(0);
+		dbg_init_debugger(nullptr);
 
 	if ( ! options.pcap_file && ! options.interface )
 		{
@@ -847,7 +847,7 @@ int main(int argc, char** argv)
 	if ( stmts )
 		{
 		stmt_flow_type flow;
-		Frame f(current_scope()->Length(), 0, 0);
+		Frame f(current_scope()->Length(), nullptr, nullptr);
 		g_frame_stack.push_back(&f);
 
 		try
diff --git a/src/util.cc b/src/util.cc
index e75e79882d..0b1128b296 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -277,7 +277,7 @@ std::string get_escaped_string(const char* str, size_t len, bool escape_all)
 char* copy_string(const char* s)
 	{
 	if ( ! s )
-		return 0;
+		return nullptr;
 
 	char* c = new char[strlen(s)+1];
 	strcpy(c, s);
@@ -558,7 +558,7 @@ const char* strpbrk_n(size_t len, const char* s, const char* charset)
 		if ( strchr(charset, *p) )
 			return p;
 
-	return 0;
+	return nullptr;
 	}
 
 #ifndef HAVE_STRCASESTR
@@ -819,7 +819,7 @@ const char* fmt_bytes(const char* data, int len)
 
 const char* vfmt(const char* format, va_list al)
 	{
-	static char* buf = 0;
+	static char* buf = nullptr;
 	static unsigned int buf_len = 1024;
 
 	if ( ! buf )
@@ -1017,7 +1017,7 @@ void hmac_md5(size_t size, const unsigned char* bytes, unsigned char digest[16])
 static bool read_random_seeds(const char* read_file, uint32_t* seed,
 				uint32_t* buf, int bufsiz)
 	{
-	FILE* f = 0;
+	FILE* f = nullptr;
 
 	if ( ! (f = fopen(read_file, "r")) )
 		{
@@ -1053,7 +1053,7 @@ static bool read_random_seeds(const char* read_file, uint32_t* seed,
 static bool write_random_seeds(const char* write_file, uint32_t seed,
 				uint32_t* buf, int bufsiz)
 	{
-	FILE* f = 0;
+	FILE* f = nullptr;
 
 	if ( ! (f = fopen(write_file, "w+")) )
 		{
@@ -1345,7 +1345,7 @@ bool is_package_loader(const string& path)
 FILE* open_file(const string& path, const string& mode)
 	{
 	if ( path.empty() )
-		return 0;
+		return nullptr;
 
 	FILE* rval = fopen(path.c_str(), mode.c_str());
 
@@ -1384,7 +1384,7 @@ FILE* open_package(string& path, const string& mode)
 	string package_loader = "__load__" + script_extensions[0];
 	reporter->Error("Failed to open package '%s': missing '%s' file",
 	                arg_path.c_str(), package_loader.c_str());
-	return 0;
+	return nullptr;
 	}
 
 TEST_CASE("util path ops")
@@ -1810,7 +1810,7 @@ FILE* rotate_file(const char* name, RecordVal* rotate_info)
 	if ( ! newf )
 		{
 		reporter->Error("rotate_file: can't open %s: %s", tmpname, strerror(errno));
-		return 0;
+		return nullptr;
 		}
 
 	// Then move old file to "<name>.<pid>.<timestamp>" and make sure
@@ -1822,7 +1822,7 @@ FILE* rotate_file(const char* name, RecordVal* rotate_info)
 		fclose(newf);
 		unlink(newname);
 		unlink(tmpname);
-		return 0;
+		return nullptr;
 		}
 
 	// Close current file, and move the tmp to its place.
diff --git a/src/util.h b/src/util.h
index c212d5d8da..66d65ba622 100644
--- a/src/util.h
+++ b/src/util.h
@@ -139,7 +139,7 @@ inline std::string get_escaped_string(const std::string& str, bool escape_all)
 
 std::vector<std::string>* tokenize_string(std::string_view input,
 					  std::string_view delim,
-					  std::vector<std::string>* rval = 0, int limit = 0);
+					  std::vector<std::string>* rval = nullptr, int limit = 0);
 
 std::vector<std::string_view> tokenize_string(std::string_view input, const char delim) noexcept;
 
@@ -167,7 +167,7 @@ extern char* strcasestr(const char* s, const char* find);
 #endif
 extern const char* strpbrk_n(size_t len, const char* s, const char* charset);
 template<class T> int atoi_n(int len, const char* s, const char** end, int base, T& result);
-extern char* uitoa_n(uint64_t value, char* str, int n, int base, const char* prefix=0);
+extern char* uitoa_n(uint64_t value, char* str, int n, int base, const char* prefix=nullptr);
 int strstr_n(const int big_len, const unsigned char* big,
 		const int little_len, const unsigned char* little);
 extern int fputs(int len, const char* s, FILE* fp);