program does not compile with newer version of g++

I have the following source code. Which compiles fine in visual studios and g++ 3.4.6; but not with g++ 4.4.3 (on a newer ubuntu machine). The newer compiler requires that I explicitly include to use atoi. I am just trying to figure out what might have change开发者_开发技巧d to cause this behavior. Is it sstream header file previously included cstdlib and no longer does so. Or is it the compiler behavior that has changed.

#include <sstream>

int main()
{
  char str1[]="123";
  int i = atoi(str1);

  printf ("value = %d",i);
  return 0; 
}

You also need to include <cstdio> for printf().

Technically, if you include the headers of the form <cname> instead of <name.h>, you also need to qualify the names from the standard library using std::. A lot of standard library implementations are relaxed when it comes to this, though, and also put the names into the global namespace.

It's implementation-dependent which headers are included by which other headers, so you should always be sure to include all the headers that you need and not assume that they will be included automatically.

I'm using GCC 4.4.5 on Debian, and the headers have changed so you will not bring in the headers necessary. You need to #include <cstdlib> and #include <cstdio> to get atoi and printf, as the compiler complained about both being missing.

#include <sstream>
#include <cstdio>
#include <cstdlib>


int main()
{
  char str1[]="123";
  int i = std::atoi(str1);

  std::printf ("value = %d",i);
  return 0;
}

Well yes. That is common. You should always include ALL headers that you are directly using and not depend on the fact that those headers are already included.

Compiler behavior is what would have changed... the <sstream> doesn't use atoi.

Arguably you should have always done #include <cstdlib>, and you'd gotten lucky with your previous compilers.

As James McNeillis points out, you should also #include <cstdio> in order to use the printf function.