Question

So I know how to place an include guard in my own header files with the standard

#ifndef ...
#define ...

Now, My question is about including libraries that are not my own. would be a good example. I have a header file which requires the use of string, so I do the following

foo.h

#ifndef FOO_H
#define FOO_H

#include <string>

... code etc ...

#endif

Now, if I have another header file called.. lets say, bar.h, which ALSO requires the use of <string>, how can i prevent multiple inclusions? Does the STL already have include guards in place?

Answer 1

The STL library also has include guards and any good library should do the same.

#ifndef _GLIBCXX_STRING
#define _GLIBCXX_STRING 1

This is from gcc’s