Conversion to char*

• The char* pointer returned by c_str( ) is const

• The pointer can only be relied on until the next non-const member of string is called:

      #include <stdio.h>
      #include <string>
      using std::string;
      void main()
      {
          string file_name = "myfile.txt";
          fopen( file_name, "r" );  // Will not compile: cannot convert
                                    // from std::string to const char *
  
          fopen( file_name.c_str(), "r" ); // Ok: use null-terminated char*
  
          char* backdoor = file_name.c_str();   // Will not compile, illegal
          const char* ptr_fname = file_name.c_str(); // Ok
          file_name.append( "blah" );                // Invalidates ptr_fname!
      }