Fix clang-tidy modernize-use-nullptr warnings

examples/matrix-topology/matrix-topology.cc

@@ -88,7 +88,7 @@ int main (int argc, char *argv[])
   //  DropTailQueue::MaxPackets affects the # of dropped packets, default value:100
   //  Config::SetDefault ("ns3::DropTailQueue::MaxPackets", UintegerValue (1000));
 
-  srand ( (unsigned)time ( NULL ) );   // generate different seed each time
+  srand ( (unsigned)time ( nullptr ) );   // generate different seed each time
 
   std::string tr_name ("n-node-ppp.tr");
   std::string pcap_name ("n-node-ppp");

examples/routing/simple-routing-ping6.cc

@@ -67,7 +67,7 @@ public:
    */
   inline void PrintRoutingTable (Ptr<Node>& n)
   {
-    Ptr<Ipv6StaticRouting> routing = 0;
+    Ptr<Ipv6StaticRouting> routing = nullptr;
     Ipv6StaticRoutingHelper routingHelper;
     Ptr<Ipv6> ipv6 = n->GetObject<Ipv6> ();
     uint32_t nbRoutes = 0;

examples/socket/socket-bound-static-routing.cc

@@ -161,7 +161,7 @@ main (int argc, char *argv[])
   Simulator::Schedule (Seconds (2.0),&BindSock, srcSocket, SrcToRtr2);
   Simulator::Schedule (Seconds (2.1),&SendStuff, srcSocket, dstaddr, dstport);
   // Fourth again as normal (goes via Rtr1)
-  Simulator::Schedule (Seconds (3.0),&BindSock, srcSocket, Ptr<NetDevice>(0));
+  Simulator::Schedule (Seconds (3.0),&BindSock, srcSocket, Ptr<NetDevice>(nullptr));
   Simulator::Schedule (Seconds (3.1),&SendStuff, srcSocket, dstaddr, dstport);
   // If you uncomment what's below, it results in ASSERT failing since you can't
   // bind to a socket not existing on a node

examples/socket/socket-bound-tcp-static-routing.cc

@@ -178,7 +178,7 @@ main (int argc, char *argv[])
   Simulator::Schedule (Seconds (2.0),&BindSock, srcSocket3, SrcToRtr2);
   Simulator::Schedule (Seconds (2.1),&StartFlow, srcSocket3, dstaddr, dstport);
   // Fourth again as normal (goes via Rtr1)
-  Simulator::Schedule (Seconds (3.0),&BindSock, srcSocket4, Ptr<NetDevice>(0));
+  Simulator::Schedule (Seconds (3.0),&BindSock, srcSocket4, Ptr<NetDevice>(nullptr));
   Simulator::Schedule (Seconds (3.1),&StartFlow, srcSocket4, dstaddr, dstport);
   // If you uncomment what's below, it results in ASSERT failing since you can't
   // bind to a socket not existing on a node

examples/stats/wifi-example-apps.cc

@@ -77,7 +77,7 @@ Sender::Sender()
 {
   NS_LOG_FUNCTION_NOARGS ();
   m_interval = CreateObject<ConstantRandomVariable> ();
-  m_socket = 0;
+  m_socket = nullptr;
 }
 
 Sender::~Sender()
@@ -90,7 +90,7 @@ Sender::DoDispose ()
 {
   NS_LOG_FUNCTION_NOARGS ();
 
-  m_socket = 0;
+  m_socket = nullptr;
   // chain up
   Application::DoDispose ();
 }
@@ -169,11 +169,11 @@ Receiver::GetTypeId ()
 }
 
 Receiver::Receiver() :
-  m_calc (0),
-  m_delay (0)
+  m_calc (nullptr),
+  m_delay (nullptr)
 {
   NS_LOG_FUNCTION_NOARGS ();
-  m_socket = 0;
+  m_socket = nullptr;
 }
 
 Receiver::~Receiver()
@@ -186,7 +186,7 @@ Receiver::DoDispose ()
 {
   NS_LOG_FUNCTION_NOARGS ();
 
-  m_socket = 0;
+  m_socket = nullptr;
   // chain up
   Application::DoDispose ();
 }

examples/stats/wifi-example-sim.cc

@@ -75,7 +75,7 @@ int main (int argc, char *argv[]) {
 
   {
     std::stringstream sstr;
-    sstr << "run-" << time (NULL);
+    sstr << "run-" << time (nullptr);
     runID = sstr.str ();
   }
 
@@ -299,7 +299,7 @@ int main (int argc, char *argv[]) {
   //--------------------------------------------
 
   // Pick an output writer based in the requested format.
-  Ptr<DataOutputInterface> output = 0;
+  Ptr<DataOutputInterface> output = nullptr;
   if (format == "omnet") {
       NS_LOG_INFO ("Creating omnet formatted data output.");
       output = CreateObject<OmnetDataOutput>();

examples/tutorial/tutorial-app.cc

@@ -20,7 +20,7 @@
 using namespace ns3;
 
 TutorialApp::TutorialApp ()
-  : m_socket (0),
+  : m_socket (nullptr),
     m_peer (),
     m_packetSize (0),
     m_nPackets (0),
@@ -33,7 +33,7 @@ TutorialApp::TutorialApp ()
 
 TutorialApp::~TutorialApp ()
 {
-  m_socket = 0;
+  m_socket = nullptr;
 }
 
 /* static */