How to forward typedef'd struct in .h

Question

I have Preprocessor.h

#define MAX_FILES 15  struct Preprocessor {     FILE fileVector[MAX_FILES];     int currentFile; };  typedef struct Preprocessor Prepro;  void Prepro_init(Prepro* p) {     (*p).currentFile = 0; } 

I realized then that I had to separate declarations from definitions. So I created Preprocessor.c:

#define MAX_FILES 15  struct Preprocessor {     FILE fileVector[MAX_FILES];     int currentFile; };  typedef struct Preprocessor Prepro; 

And Preprocessor.h is now:

void Prepro_init(Prepro* p) {     (*p).currentFile = 0; } 

That obviously, doesn't work because Pr..h doesn't know Prepro type. I already tried several combinations, none of them worked. I can't find the solution.

Answer 1

Move the typedef struct Preprocessor Prepro; to the header the file and the definition in the c file along with the Prepro_init definition. This is will forward declare it for you with no issues.

Preprocessor.h

#ifndef _PREPROCESSOR_H_ #define _PREPROCESSOR_H_  #define MAX_FILES 15  typedef struct Preprocessor Prepro;  void Prepro_init(Prepro* p);  #endif 

Preprocessor.c

#include "Preprocessor.h"  #include <stdio.h>  struct Preprocessor {     FILE fileVector[MAX_FILES];     int currentFile; };  void Prepro_init(Prepro* p) {     (*p).currentFile = 0; } 

Answer 2

If you want to hide the definition of Preprocessor, you can simply put this in the header file :

struct Preprocessor; typedef struct Preprocessor Prepro; 

But more generally, you'll probably also need the Preprocessor definition in the header file, to allow other code to actually use it.