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 ty开发者_开发百科pe. I already tried several combinations, none of them worked. I can't find the solution.

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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;
}

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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.

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You have put in .c what should be in .h, and vice versa. Prepro_init must be in .c file, and that file must #include "Preprocessor.h".

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YAS:Yet Another Solution.

Preprocessor.h

<some code>
    void Prepro_init(Prepro* p) {
        (*p).currentFile = 0;
    }
<some code>

Preprocessor.c

#define MAX_FILES 15

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

#include "Preprocessor.h"      //include after defining your structure.

         <some code> 
        {
              struct Prepro p;
              Prepro_init(p);
     <some code> 
          .... using p.currentFile.....
          .....using other members....
     <some code> 
        }
           <some code> 

Now it will work. I think this is your requirement. Hope it helps.

Drawback: The members of the structure Preprocessor, must be predetermined. i.e the header file uses the member currentFile. So, c file which includes Preprocessor.h must have a structure which is typedefined as Prepro and that structure must include a member currentFile.(in this case).

The same problem I had a year before, while writting a header file to display a users Avl tree in a graphical tree format.

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I would suggest that you follow Linus[1], and do not use typedef struct.

If you are in control over the library:

Include file

struct Foo;

int foo_get_n(const struct Foo *bar);

In implementation file

struct Foo
{int n;};

int foo_get_n(const struct Foo *bar)
{return bar->n;}

If you are not in control over the library:

Ask the maintainer to remove these polluting typedefs from the include files.

Summary

Do not use typedef struct.

[1] http://yarchive.net/comp/linux/typedefs.html

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Swap .h and .c file. Include header in .c.

Also refer to a book about declarations, definitions and what header files do.