KeithRB:
"I can't use it in a #include as its only a define."

In traditional C, that is exactly where #defines are supposed to go!

If you are worried about name space collision you can make them "idimpotent":

ifndefined(API_KEY_FILE)

#define API_KEY_FILE
#define my_api_key
#endif

I'm afraid you've completely lost me.

Should I create a file, say "api_key_file" and it in put the apikey. Then use the above code in my main program?