Why the C structure definition in the implementation file is unavailable? -

i give following example illustrate question:

1) a.h structure declared

 a.h     struct a_structure;     typedef struct a_structure *a_structure_ptr; 

2) b.c structure definition implemented

 #include "a.h"   struct a_structure  {     int a;     int b;     int c;   }; 

2) main.c structure invoked

#include <stdlib.h> #include "a.h"  int main () {    struct a_structure b;     return 0;  } 

however, cannot compile these c codes receive following error message:

>main.c(6): error c2079: 'b' uses undefined struct 'a_structure' 

any ideas? thank in advance.

edit:

#include <stdlib.h> #include "a.h"  int main () {    struct a_structure *b=0;    b=(struct a_structure*)malloc(12);    b->a=3;    free(b);     return 0;  } 

i tried create structure in way still failed.

you need this:

struct a_structure {     int a;     int b;     int c;  }; 

in a.h

this typical approach when defining structs

if you're trying implement opaque pointer, need function instantiates a_structure , returns pointer, functions manipulate a_structure pointers:

in a.h

a_structure_ptr createa(int a, int b, int c);   void freea(a_structure_ptr obj); void seta_a( a_structure_ptr obj, int ); int  geta_a( a_structure_ptr obj ); // etc. 

in b.c

a_structure_ptr createa(int a, int b, int c) {      a_structure_ptr s = malloc( sizeof(a_structure) );      s->a = a;      s->b = b;      s->c = c; }  void freea(a_structure_ptr obj) {     free( obj ); }  void seta_a( a_structure_ptr obj, int ) {     obj->a = a; } 

in main.c

int main () {     struct a_structure *b = createa( 1, 2, 3);     seta_a( b, 3 );     freea(b);     return 0; }