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Full Discussion: C language Header files
Top Forums Programming C language Header files Post 302476739 by Corona688 on Thursday 2nd of December 2010 11:20:41 AM
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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LEARN ABOUT DEBIAN

gvrng

gvrng(1)																  gvrng(1)

NAME

       gvrng - An interactive, introductory programming language.

SYNTAX

       gvrng [world file | program file]

DESCRIPTION

       Guido van Robot is a project developed by advanced high school students for use by their peers as a learning tool and precursor to the fur-
       ther study of programming with Python. It is a minimalistic programming language providing just enough syntax to help  students	learn  the
       concepts  of  sequencing, conditional branching, looping and procedural abstraction. It's biggest strength is that it permits this learning
       in an environment that combines the thrill of problem-solving with instant visual feedback. In short, it is  an	interactive,  introductory
       programming  language that is excellent for learning the basic concepts of programming, applicable in any high-level language. Best of all,
       it's a whole lot of fun, too!

       At this point, you are probably asking yourself, "What is GvRng, specifically?" The gist of it is that it is a robot represented by a  tri-
       angle  on  the screen that moves around in a world made up of streets and avenues, walls and "beepers", which Guido can collect or set. His
       actions are completely guided by a program written by the user.

FILES

       /usr/bin/gvrng
       /usr/lib/gvrng
       /usr/share/doc/gvrng

AUTHORS

       Stas Zytkiewicz - stasz@linux.isbeter.nl
       Waseem Daher - wdaher@mit.edu
       Steve Howell - showell@zipcon.net

SEE ALSO

       http://gvrng.sourceforge.net

Stas Zytkiewicz 						  1.0  09/13/2004							  gvrng(1)
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