Found something cool in C11

c.h
typedef int i;
extern int shi;

c.c
#include "c.h"
#include "c.h"
#include "c.h"

int shi;

int
main (void)
{
return 0;
}

As you can see C11 allows multiple typedefs of the same type to the same type, a typedef long i; would be illegal
This avoids the need for include guards but sadly it does not work for structs, not that this is a problem

>>7
It is, read the standard, it says that multiples declarations in the file scope (which implies multiples tentatives definitions) are ok.

Also, you can set what standard you wanna use in gcc.