Programming

Hi I have a program, say file1.c which included file1.h, the header file which had lots of #define macros and structure definitions used by file1.c

I have decided to split the source code into 3 separate files (for logical reasons)

file1.c
file2.c
file3.c

Each of these have a corresponding header file which contain only function prototypes:

file1.h (I renamed the earlier file1.h, which had all the #defines and structure defs. to, say, abc.h)
file2.h
file3.h

So, Earlier everything was in file1.c. I removed a set of related functions and put them in file2.c, And another set of related functions and put them in file3.c


file1.c includes...

Code:

#include "file2.h"
#include "file3.h"
#include "abc.h"

file2.c includes..

Code:

#include "file1.h"
#include "abc.h"

file3.c includes..

Code:

#include "file1.h"
#include "abc.h"

Now my question is:

1) What would be an appropriate name for abc.h ?? This has lots of #define macros and structure definitions which is used by all three source files (file1.c, file2.c and file3.c) and hence is #included by all 3 of them.

2) Suppose the original source code had LOTS of global variables. The variables are used by all 3 source files. So how do I deal with them ? Can I put all these global variables in a header file and include it in all the 3 source files ? Will that work ? Or should I leave the global variables in file1.c and then declare them as "extern" in file2.c and file3.c ? (keeping in mind that there are LOTS of them).

3) Can header files contain variable declarations/definitions ???

What happens if I have a header file which has:

int a = 5

and I include this file in a some .c file and use 'a' and change its value ?

Thanks in advance..

1. Make the header file names have some relation to their contents.

2. Dont put global definitions in headers, only put "extern" references to them, I recommend don't put externs in source files.

eg have extern int myFoo,myBar;

3. Only define actual globals once in a source file

Think of it this way....

* A source file is a private implementation file.

* A header file describes the public interface to that implementation.

If you change a global variable, say from an int to a long, then you only have to change it in the specific source it's declared, and the header for that same file, not in a number of other source files.

Hey thanks for your reply.

Sorry porter, I did not understand.. should I put global variables in a header file or in a source file ?

So, say in file1.c I have declared a global variable: int x

Then in file2.c I have declared it as extern: extern int x

Now if I change int x to long x, that means I have to change it in multiple files right? file1.c and file2.c

Oh I think I now understand what you mean..

I should declare all global variables in a header file as extern. And define it in only one source file...

Something like this...

file1.c

Code:

#include "globals.h"
int a;
int b;
int c;
main()
{
     a = 1;
     b = 2;
     c = 3;
}

globals.h

Code:

extern int a;
extern int b;
extern int c;

file2.c

Code:

#include "globals.h"
func2()
{
     a++;
     b++;
     c++
}

Go to the top of the class!

duplicate post

I like using definitions in header's and sources to do this also, like so:

file.h

Code:

#ifndef _FILE_H
#define _FILE_H

#ifdef _FILE_C
#define _FILE_C_CLASS
#else
#define _FILE_C_CLASS extern
#endif

_FILE_C_CLASS int a;
_FILE_C_CLASS int b;

#endif

The top defintion (_FILE_H) prevents recursive includes of the header, common practice.

The next will define all the globals as extern unless _FILE_C is defined. Of course, in file.c you'd define that before including file.h as follows:

file.c

Code:

#define _FILE_C
#include "file.h"

/* source */

#undef _FILE_C

This way I know that one and only one C file (the one that defined _FILE_C, which should be file.c) contains the definitions of all the globals.

Meh...just my personal style that I picked up...sometimes I'll do this too:

file.h

Code:

_FILE_C_CLASS int a
#ifdef _FILE_C
= 5
#endif
;

This is probably arguable whether or not it is good, because it tells the "user" including the header what the initial value of the variable is, which you may want to hide.