implicit declaration warning only when using std=c99

[Glen Beane]

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