I have an odd problem with my current project in that I get the above error when I compile.
I have a number of different files that are included into a main.h which is then included into main.c where this error is occurring but I can call other functions from the same .c file without any problem. The code itself does actually work and the function complained about is called correctly.
I appreciate this is vague without code, and I can happily post code, but there's a lot of it and I'm not at all convinced that if I pare it down to an example that I'll get the same error.
maps.h >> includes spike.h, isometric-engine.h
tiles.h >> includes spike.h, isometric-engine.h
isometric-engine.h >> includes spike.h
isometric-engine.c >> includes isometric-engine.h
main.h >> includes spike.h, isometric-engine.h, tiles.h, maps.h
main.c. >> includes main.h
void set_viewport(int x, int y); is prototyped in isometric-engine.h, defined in isometric-engine.c and called in main.c and is the function that is causing the warning. draw_map is defined and called in exactly the same places but doesn't cause a warning!?