forgot to use std::string instead of const char *

src/internet-node/ipv4-header.cc

@@ -30,7 +30,7 @@ namespace ns3 {
 
 bool Ipv4Header::m_calcChecksum = false;
 
-const char *
+std::string
 Ipv4Header::GetUid (void)
 {
   return "Ipv4Header.ns3";

src/internet-node/ipv4-header.h

@@ -32,7 +32,7 @@ namespace ns3 {
 class Ipv4Header : public Header 
 {
 public:
-  static const char *GetUid (void);
+  static std::string GetUid (void);
   /**
    * \brief Construct a null IPv4 header
    */