Thread: trying to split some code into two files, error

Post the smallest and simplest compilable program that works when it is a single file, and also post the same program split into two files, such that the split demonstrates this error message that you encountered.

You probably made a typo error or something somewhere, but without code to see, I can only vaguely tell you that you made a mistake, which you already know to be true.

Originally Posted by BpB

should #defines associated with the functions I'm putting in the second files, be in the .h or .c file? Probably doens't matter technically, but what's the best practice?

It depends on whether they are meant to be "internal" or "external" to the translation unit. If they are "external", then they go in the header, otherwise they might go in the source file instead, with extra care for appropriate naming conventions to avoid name collision.

Stuff that's defined in the first main c file, should that be also in a .h file and include it from the second .c file?

So not
test1.c (with main() and include test2.h)
test2.h
test2.c

But
test1.h
test1.c (with main() and include test2.h)
test2.h
test2.c (with include test1.h)

Originally Posted by BpB

Stuff that's defined in the first main c file, should that be also in a .h file and include it from the second .c file?

That depends on what you have in mind for the organisation of your code.

You could start with this simple organization and then modify it as you see fit:

main.c <-- this #include's other .h files

module1.h
module1.c

module2.h
module2.c

...

Compile each one and link them together:

Code:

bash$ gcc -c module1.c -o module1.o
bash$ gcc -c module2.c -o module2.o
bash$ gcc -o main main.c *.o
bash$ ./main

Each module looks something like this:

Code:

#include "module1.h"
#include <stdio.h> // If your module needs stdio, etc.
// etc...

Each module header looks like this:

Code:

int f1(); // E.g. this function defined in module1.c

And main looks like this:

Code:

#include "module1.h"
#include "module2.h"
//...
//etc

Once you have that basic structure, rename things, add on and remove as desired to make whatever organization you want. It is convenient to add include guards to header files so that the ordering does not matter. The following is the unofficial way to make an include guard. It is unofficial but every compiler supports it:

Code:

#pragma once
// Rest of header file