Implicit Declaration Warning (C99 Linux)

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February 1st, 2013, 11:23 AM

jakotheshadows

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Implicit Declaration Warning (C99 Linux)

I'm using waitid and getting the following warning:
Prog1.c:84: warning: implicit declaration of function ‘waitid’

Here are my #includes:

#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <assert.h>

I vaguely remember having a similar problem in the past, but I don't remember what I did about it and google isn't being terribly helpful today. The man page for waitid says to include sys/types and sys/wait so I'm not really sure what I'm missing.

Code:

				waitid(P_PID, pid1, 0, WEXITED);
				printf("p1 exited\n");
				waitid(P_PID, pid2, 0, WEXITED);
				printf("p2 exited\n");
				waitid(P_PID, pid3, 0, WEXITED);
				printf("p3 exited\n");

February 1st, 2013, 11:49 AM

dwise1_aol

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Read those header files (or grep in their directory) to find waitid(). It might not be supported. I had certainly never heard of it (which doesn't mean anything), though I have heard of waitpid.

Looking for it in those header files should solve your mystery.

February 1st, 2013, 11:49 AM

Scorpions4ever

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Perhaps you might need to #define a macro. The man pages do mention this for waitid:

Quote:

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

waitid():
Since glibc 2.12:
_POSIX_C_SOURCE >= 200809L || _SVID_SOURCE ||
_XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
Before glibc 2.12:
_SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

Try adding -D_SVID_SOURCE in your gcc command line perhaps (or #define _SVID_SOURCE before your #include <sys/wait.h> line) and see if that solves it.

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February 1st, 2013, 12:51 PM

jakotheshadows

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Quote:

Originally Posted by Scorpions4ever

Perhaps you might need to #define a macro. The man pages do mention this for waitid:

Try adding -D_SVID_SOURCE in your gcc command line perhaps (or #define _SVID_SOURCE before your #include <sys/wait.h> line) and see if that solves it.

Yep it was definitely something like that. I checked code I did for my systems programming course and saw a similar macro, so I defined it in my current project and the warning disappeared. Problem solved.

Implicit Declaration Warning (C99 Linux)

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