Question

In VC++, when I typecast the const char* value returned by std::string::c_str() to char* and print the casted value, nothing gets printed on the screen. Here is the code snippet

#include "stdafx.h"
#include <string>

using namespace std;

string test() { return(string("HELLO"));}


int _tmain(int argc, _TCHAR* argv[])
{
  char* val;
  val = (char*) test().c_str();
  printf("\n %s\n", val);
  return 0;
}

When I simply check the ASCII value at val[0] it is 0. But under G++, the text HELLO gets displayed.

Is the cast from const char* to char* a non-standard one whose results are not defined?

Answer 1

The cast is fine as long as you don’t modify the value or read from it after altering the string (you should get at least a warning though).

The problem is that you call the function on a temporary (the temporary is the string returned by cat()). After the ;, the temporary goes out of scope and val still points to memory managed by the temp. It’s UB reading from it.