CODEWITHSUNDEEP
cdeclarationimplicit
Ericson Willians
Ericson Willians

Reputation: 7855

C - Very Strange Implicit Declaration

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!

Upvotes: 0

Views: 418

Answers (3)

Potatoswatter
Potatoswatter

Reputation: 137940

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.

Upvotes: 1

Ericson Willians
Ericson Willians

Reputation: 7855

I recreated the header file, without altering anything, and it worked. It really had something to do with me never altering the file (I mean, renaming the file or excluding it). Some very underground compiling issue happened.

Upvotes: 0

lxop
lxop

Reputation: 8625

I tried creating a couple of simple files like you've described here, but I don't get any problems. So:

  • are you sure you used the same name for the new function in both draw.h and main.c (really sure)?

  • I don't know about allegro: does it happen to have a function called TileSystem in it?

Beyond those, I would recommend starting with a bare bones setup (so just the include, the main function, and the call in main.c, and just the declaration in draw.h), make sure that compiles with gcc main.c -std=c99 -o main, and then build your application up to what it is currently, piece by piece, until the error starts happening again. That should help you identify the source of the problem.

Upvotes: 0

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