gcc warning: implicit declaration of function

Hi all!

This is my first post in here. I disliked C for a long time, but now that I'm getting the hang of it, I like to do stuff with it.

I'm getting a 'Implicit declaration of function' warning. This happens usually when the function that is being called is not defined, nor it's prototype.

make all:

Code:

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gcc -ansi -pedantic -Wall -c main.c
main.c: In function 'main':
main.c:4: warning: implicit declaration of function 'newGameArea'
main.c:4: warning: initialization makes pointer from integer without a cast
gcc -ansi -pedantic -Wall -c functions.c
gcc -ansi -pedantic -Wall -c gamearea.c
gcc -ansi -pedantic -Wall -c heightmap.c
gcc -ansi -pedantic -Wall -c position.c
gcc -ansi -pedantic -Wall -c tetromino.c
gcc -o "proj2" main.o functions.o gamearea.o heightmap.o position.o tetromino.o

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main.c includes it's own header file, main.h

main.h includes every other header file:

Code:

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#pragma once
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "constants.h"
#include "functions.h"
#include "position.h"
#include "tetromino.h"
#include "heightmap.h"
#include "gamearea.h"

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main.c (line 4):

Code:

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GameArea *gameArea = newGameArea();

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The function that is missing, is prototyped on gamearea.h:

Code:

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GameArea* newGameArea();

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I'm really clueless on what is going on. I'd appreciate some help :) Thanks!

anatoly

Do other header files include gamearea.h ?

Does gamearea.h have #ifndef FILE_INCLUDED type guards in it?

Did you copy/paste those guards from another file?

You can generally do without #pragma once, as it is not entirely portable.

I'm old school, so I never do that kind of thing. On gamearea.h, your prototype should explicitly have parameter of (void):

GameArea* gameArea(void);


Then:
GameArea *gameArea;
//when you're ready to call the function:
gameArea = newGameArea();

I'm not at all familiar with your compiler, but that's how I'd do it.

Hey!

Thanks for the quick replies.

I (probably) accidentally solved it. Not sure what I did. I just closed the IDE in rage, and when I came back and did the makeclean-makeall thing, everything compiled without any errors or warnings.

The target computers (that are going to compile this) are all 'equipped' with the GNU C Compiler, and currently has full support for the "#pragma once" directive. If the need arrises, I'll replace it with "#ifndef"s. :) I thought the GCC was one of the most popular compilers out there though, but I guess there are some that won't accept "#pragma" :)

I'll clean up the whole code with your suggestions (use void instead of nothing, use ifndef instead of pragma, and split variable creation from giving it a value) - since I (try to) follow the C programming standards - if I have the time :) (I need to finish this within 25h 30m - caffeine levels increasing)

Thanks again :)

- anatoly

Quote:

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Originally Posted by anatoly

I (probably) accidentally solved it. Not sure what I did. I just closed the IDE in rage, and when I came back and did the makeclean-makeall thing, everything compiled without any errors or warnings.

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This sounds like the make file does not contain information about header dependencies. Make can automatically deduce which .c files are needed to generate a .o file. But it cannot read a .c file to figure out which headers are needed. Therefore, unless you have a script that automatically updates the make file when you add headers, when ever you change a header you need to manually recompile all the .c files that use it. Some IDEs have this problem, others are smarter. I recall DevC++ had this issue.