http://cplus.about.com/library/weekly/aa060402d.htm
http://www.subduck.com/vb/showthread.php?s=&threadid=89

First two links from a google search for "multiple files c".
Haven''t looked at them exactly, but they seem usable.

The basics in short:

- Don''t put any code in header files, only forward declarations and other declarations (structs, typedefs...). You would get duplicate definitions otherwise.

- If you want to use a variable from another file:



"George W. Bush Geography Simplification Initiative"

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In a nutshell, group functions that operate on similar items together in the same source file and add source files to the project (don''t include them like headers). Typically, function prototypes, structure typedefs and preprocessor defines associated with a particular source file are placed into the corresponding header for that file. The primary factor to decide whether a given item should be put into the header or left in the source is whether or not that item should be reachable by other source files. For example, lets say your project has two source files, winmain.c and gldraw.c. There are functions in gldraw.c that you want to call from winmain.c, so you put the prototypes for those functions into gldraw.h and then add #include "gldraw.h" to winmain.c. If there are other functions in gldraw.c that you don''t want to call from winmain.c - and that you don''t plan on calling from any file other than gldraw.c - don''t put those prototypes into gldraw.h. These functions can also be declared static. That limits their use to the file where they are declared. This is different than declaring a variable inside of a function to be static. The extern keyword tells the compiler to hold open a slot for the item. It''s sort of like saying, whatever it is, this thing here is defined externally - ie in some other file in this project.