Thread: multiple include doesn't give compile error

Hi All

I have a main file (main.c) which includes show.h and show1.h
But show1.c also includes show.h. show.h looks like

Code:

void init() ;
void show() ;
void set(int x) ;
int *get() ;

extern int  *y ;

Because it is included twice I was expecting compile errors, but the program compiles/runs fine, why ?
I thought, in this situation, I needed things like #ifndef .... #endif!

Below are the listings of all the files

main.c

Code:

#include "show.h"
#include "show1.h"

int main(int argc, char *argv[])
 {
   init() ;
   set(10) ;
   show() ; 

   set(20) ;
   show() ; 

   // -------
   show1() ;

   set(303) ;
   show1() ;
   return 0 ;
 }

show.c

Code:

#include <stdlib.h> // malloc
#include <stdio.h>  // printf

#include "show.h"

int *y ;

void init() {
  y = malloc(sizeof(int)) ;
}

void set(int x) {
  *y = x ;
}

int * get() {
  return y ;
}

void show() {
  printf("value is %d\n", *y) ;
}

show.h (see above)
show1.c

Code:

#include <stdio.h>  // printf
#include "show.h"

extern int* y ;

void show1() {
  printf("the value is %d\n", *y) ;
  show();
}

show1.h

Code:

void show1() ;

I see, so it has todo with header files including each other

cheers