Question

I had a function in a file “draw.h”:

void TileSystem() {
    // Some code here.        
}

And in the “main.c” file, I call it, because I have #included “draw.h” in the file. The function works nicely well!!

But then, I decide to rename the function to

void CreateTileSystem() {
    // Some code here.        
}

And I get the following output:

gcc main.c -std=c99 -o main `pkg-config --cflags --libs allegro-5.0 allegro_acodec-5.0 allegro_audio-5.0 allegro_color-5.0 allegro_dialog-5.0 allegro_font-5.0 allegro_image-5.0 allegro_main-5.0 allegro_memfile-5.0 allegro_physfs-5.0 allegro_primitives-5.0 allegro_ttf-5.0`
main.c: In function ‘main’:
main.c:217:12: warning: implicit declaration of function ‘CreateTileSystem’ [-Wimplicit-function-declaration]
/tmp/cclNEg6q.o: In function `main':
main.c:(.text+0xb1e): undefined reference to `CreateTileSystem'
collect2: error: ld returned 1 exit status
make: *** [main] Error 1

And then, I just rename it back to TileSystem and works well. I have no other references in the entire code. It makes no sense at all! I want to rename, in order to use verbs in functions (A more “correct” standard, I think). Well, I would really like to know what happens. I really CAN’T find errors, and the fact that when I rename it, it backs to work, frustrates me even more.

Thank you very much!

Answer 1

You have to also change the name in the header file, draw.h.

That error/warning indicates that there was no forward declaration for the function, which in older C dialects results in an assumption that the function is int fn(int) (if memory serves).

It works when you change it back because the header was never modified, so it’s still providing a forward declaration of the old name.