C - multiple definition of function during building large project -

i'm trying build large project , in have following header file

error.h

#ifndef __error_h__ #define __error_h__  #include <stdio.h> #include <stdlib.h>  void error_validate_pointer(void *ptr) {     if (ptr == null)     {         puts("error allocating memory");         exit(1);     } }  #endif /* __error_h__ */ 

i use function in every .c file have (i include "error.h" in every file) thought #ifndef protect me multiple definition error. yet, during building, following errors:

../dictionary/libdictionary.a(state_list.c.o): in function `error_validate_pointer': /home/pgolinski/dokumenty/programowanie/spellcheck-pg359186/src/dictionary/error.h:8: multiple definition of `error_validate_pointer' ../dictionary/libdictionary.a(hint.c.o):/home/pgolinski/dokumenty/programowanie/spellcheck-pg359186/src/dictionary/error.h:8: first defined here ../dictionary/libdictionary.a(state_set.c.o): in function `error_validate_pointer': /home/pgolinski/dokumenty/programowanie/spellcheck-pg359186/src/dictionary/error.h:8: multiple definition of `error_validate_pointer' ../dictionary/libdictionary.a(hint.c.o):/home/pgolinski/dokumenty/programowanie/spellcheck-pg359186/src/dictionary/error.h:8: first defined here 

what reason keep getting these errors? how avoid it?

it's happening because #include definition several times, end having multiple definitions - 1 every file include in.

change code to

#ifndef __error_h__ #define __error_h__  #include <stdio.h> #include <stdlib.h>  void error_validate_pointer(void *ptr);  #endif /* __error_h__ */ 

... header, contains declaration of function.

then create new file (e.g. error.c) definition

#include "error.h"  void error_validate_pointer(void *ptr) {     if (ptr == null)     {         puts("error allocating memory");         exit(1);     } }