Question

#include <stdio.h>
#include <stdio.h>

int main ()
{
   printf ("hello world");
   return 0;
}

when I compile this, the compiler doesn’t give any warning/error for including stdio.h twice. Why is it so? Aren’t the functions scanf, printf etc. declared and defined twice now?

Thanks, in advance

Answer 1

Typically, header files are written similar to the below example to prevent this problem:

#ifndef MYHEADER
#define MYHEADER

...


#endif

Then, if included more than once, then 2nd instance skips the content.