implicit declaration warning only when using std=c99

2 msg	different versions of gcc for kernel and usersp...
8 msg	GCC ARM Cross Linker Problem
2 msg	GCC enquires
1 msg	Read and get back(It Urgent)
3 msg	How to list all public symbols in a file/project?
1 msg	mudflap warning: unaccessed registered object:
2 msg	gcc -fstack-protector-all option
3 msg	Linker Problem Help Required
3 msg	global objects order-of-construction & orde...

implicit declaration warning only when using st...
\ Glen Beane (17 Aug 2006)
. \ Ian Lance Taylor (17 Aug 2006)

2 msg	Using a lower version of gcc
3 msg	is compiler error?
2 msg	math functions
1 msg	Compiling Simplescalar
1 msg	Segmentation fault problem with C & Inline ...
2 msg	Help gcc compilation on Solaris 8
6 msg	Understand cross compiling
1 msg	compilation time increased from 10 sec to 24 sec
1 msg	gcc 4.1.1 problem creating C++ shared library
2 msg	expected declaration specifiers or ... before (...

Subject:	implicit declaration warning only when using std=c99
Group:	Gcc-help
From:	Glen Beane
Date:	17 Aug 2006

I have been developing a C program using gcc 4 on Apple OS X. Today I copied my source over to a quad core AMD Opteron box running SuSE linux with gcc v 3.3.3 and compiled.

I have been compiling this program with -std=c99 so that I can declare variables inside of a for loop statement
e.g. for (int i = 0; i <foo; i++)

on the suse box, I would get implicit declaration warnings for strdup, strtok_r, and lstat. I verified that I was including the proper .h files, and no such warnings were produced on the OS X box.

I made the following test program and determined that I only got the warning if I used -std=c99. -std=gnu99 did not produce warnings, nor did the default std. I then tried compiling the test program with -std=c99 -D_GNU_SOURCE and it did not produce the warnings. What is it about -std=c99 on this system that requires _GNU_SOURCE to be defined in order for the prototypes for strdup, strtok_r, and lstat to be properly included? Should I just compile my program with -std=gnu99 and forget about it?

test program:

#include <string.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
char *str = strdup(argv[0]);

printf("%s\n", str);

return 0;

}

--
Glen L. Beane
Software Engineer II
The Jackson Laboratory
Phone (207) 288-6153