On Wed, 2008-06-18 at 17:07 +0200, Quentin Mathé wrote:
> The man page example works for me too.
I realize now that this example doesn't help -- it includes getopt.h,
rather unistd.h, because it uses long options. I have attached a
modified example which uses standard getopt and includes unistd.h.
> After some experiments, I have found the problem comes from passing
> the flag -std=c99 to GCC. The example fails to compile with it, unless
> I pass -D_GNU_SOURCE or I use -std=gnu99 instead of c99.
> I'm not sure why I observe this behavior. I suppose getopt() is a
> posix extension not part of the C99 standard lib. On Linux (at least
> Ubuntu), posix extensions are enabled by default except for c99 (and
> probably other strict ISO C versions). Is my reasoning correct?
I agree with you. "-std=c99" seems to be equivalent to passing
"-std=gnu99 -ansi", where the "-ansi" restricts to ANSI standard (more
or less; according to the GCC info page, to be really strict you must
add "-pedantic"). Same with "-std=c89" and just "-ansi", since
"-std=gnu89" is the default.
> I think David Chisnall wrote this code for FreeBSD initially. So this
> point doesn't seem to hold for FreeBSD.
Exactly. To the extent that one is picky about standards compliance,
this is a bug with FreeBSD's libc headers. Of course, it's also a
pragmatic solution to just declare getopt and be done with it, since it
doesn't conflict with an older identifier.
> Thanks for the help :-)
No problem. Thanks for writing clean code -- someone less careful
would just include getopt.h and move on :)
Sourav
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main (int argc, char **argv) {
int c;
while(1) {
c = getopt(argc, argv, "abc:d:");
if(c == -1) break;
switch(c) {
case 'a':
printf ("option a\n");
break;
case 'b':
printf ("option b\n");
break;
case 'c':
printf ("option c with value '%s'\n", optarg);
break;
case 'd':
printf ("option d with value '%s'\n", optarg);
break;
case '?':
break;
default:
printf ("?? getopt returned character code 0%o ??\n", c);
}
}
exit(0);
}
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