Thread: define functions in another file

We just had a discussion about this not too long ago. Take a look at this thread. It should answer all your questions.

Originally Posted by suryak

The variables that I commonly used in main and this files have to be declared before I write main()..

Avoid global variables. Instead, write function that accept arguments and work on them. These functions can then do one thing and do it well, and it becomes easier to reason about your program because you only need to consider those parameters and local variables.

If you persist with unnecessary use of global variables, dividing your code into functions will only be of minimal use since you would have to keep checking if the global state is changed whenever you call a function.

Originally Posted by suryak

how do I include these files in main().

It depends. If you want to add the directory they are in to the include file search path, take a look at the gcc documentation: Options for Directory Search.

Originally Posted by suryak

As far as from the above discussion.. I decided to use extern for common variables that are involved in all modules. but does it solve my matter...?

NO! In terms of getting your program to compile and link, it may "solve" your problem, but you should strictly avoid global variables until you have acquired more experience that will allow you to make a sound decision on whether global variables are appropriate. Sure, those variables may be common to all modules, but that in itself does not mean that they should be global.

Originally Posted by suryak

if I have mod1.c, mod2.c which have some function definitions .. mod1() & mod2()
how do I call them in main().. As those functions are defined in separate file..how to I include them in main()

You need to place their prototypes in a header file that is included.

Originally Posted by suryak

is this correct way to write in main file.. main.c which contain main()

# include <mod1.c>
# include <mod2.c>

Probably not because you would be including source files rather than header files, if the .c extension is a valid clue.

Typically, you would have your own header files which have your function prototypes in them. Then you would include these header files in your main project file. Additionally, these header files would be included in your module files which would define your functions. We have an example here - multiple source files FAQ. It uses C++ but should give you the idea.

If the files are in the same directory, it would be:

#include "mod1.h"
#include "mod2.h"

Also note Laser's link about setting up your directory search options with gcc.

EDIT: The angle brackets < > tell the compiler to look in the system header files but it doesn't look in the current directory by default. Hence Laser's link.

Originally Posted by suryak

instead of building mod1.c and mod2.c ..
I made mod1.h and mod2.h

added

#ifndef mod1_H
#define mod1_H
and at the end, i added
#endif

and in the main.c ..
I add

# include <mod1.h>
# include <mod2.h>

This might be correct, but generally, it isn't. Normally, we would do something like this:

Code:

#ifndef FOO_H
#define FOO_H

/* foo.h */

void foo(int n);

#endif

Code:

/* foo.c */

#include <stdio.h>

void foo(int n)
{
    printf("This is foo: %d\n", n);
}

Code:

/* main.c */

#include <stdio.h>
#include "foo.h"

int main(void)
{
    printf("%s\n", "Hello world!");
    foo(123);
    return 0;
}

Originally Posted by suryak

when I complile .. its showing " no such file or directory found.."

what's the problem..how do i fix it.

Refer to the link in my post #5.