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# 1  
Old 12-02-2010
C language Header files
Hi people I'm trying to do a school project and I've a situation wich is bothering me, imagine We've a program and that programs devided in multiple files "dotC1.c" and "dotC2.c" (for example) and they include our own header "header.h", and if We are using some libraries int both files it would make sence if I just include then in "header.h"? I'd apreciate if someone just help me thank you.
# 2  
Old 12-02-2010
The normal way to develop a C project is with C modules, like you describe: file1.c file2.c
plus there may be a header file, and a makefile

Let's call "file.h" the common required header file. Most projects though are much larger and there can be lots of specialized header files. I would take a look at some gnu source code to get an idea of how this all works.

Coreutils - GNU core utilities
# 3  
Old 12-02-2010
All header files do is declare the existence of a function. For instance, you have a library 'flogify' or something.

Code:
// flogify.c
#include <stdio.h>
#include "flogify.h"

int flogify(const char *oops)
{
        return(printf("flogify(%s)\n", oops));
}

Code:
//flogify.h
// #ifndef/#define/#endif prevents accidental multiple inclusion.
#ifndef __FLOGIFY_H__
#define __FLOGIFY_H__

extern int flogify(const char *);

#endif/*__FLOGIFY_H__*/

so a.c and b.c will know the function exists. But you have to link it, too, otherwise it'll complain it can't find it:

Code:
$ gcc a.c b.c -o flogify
/tmp/ccEYKx87.o: In function `main':
a.c:(.text+0x19): undefined reference to `flogify'
/tmp/ccNOvwnB.o: In function `other':
b.c:(.text+0xe): undefined reference to `flogify'
collect2: ld returned 1 exit status
$ gcc a.c b.c flogify.c -o flogify
$

In other words, header files just tell code how to use functions, they don't actually make the functions exist.
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