Organization of C files

Question

I\'m used to doing all my coding in one C file. However, I\'m working on a project large enough that it becomes impractical to do so. I\'ve been #including them together but

Answer 1

The .h files should be used to define the prototypes for your functions. This is necessary so you can include the prototypes that you need in your C-file without declaring every function that you need all in one file.

For instance, when you #include <stdio.h>, this provides the prototypes for printf and other IO functions. The symbols for these functions are normally loaded by the compiler by default. You can look at the system's .h files under /usr/include if you're interested in the normal idioms involved with these files.

If you're only writing trivial applications with not many functions, it's not really necessary to modularize everything out into logical groupings of procedures. However, if you have the need to develop a large system, then you'll need to pay some consideration as to where to define each of your functions.

Answer 2

Compiler

You can see an example of a C 'module' at this topic - Note that there are two files - the header tea.h, and the code tea.c. You declare all the public defines, variables, and function prototypes that you want other programs to access in the header. In your main project you'll #include and that code can now access the functions and variables of the tea module that are mentioned in the header.

It gets a little more complex after that. If you're using Visual Studio and many other IDEs that manage your build for you, then ignore this part - they take care of compiling and linking objects.

Linker

When you compile two separate C files the compiler produces individual object files - so main.c becomes main.o, and tea.c becomes tea.o. The linker's job is to look at all the object files (your main.o and tea.o), and match up the references - so when you call a tea function in main, the linker modifies that call so it actually does call the right function in tea. The linker produces the executable file.

There is a great tutorial that goes into more depth on this subject, including scope and other issue you'll run into.

Good luck!

-Adam