According to getopt(3) the variables optarg, optind, etc. are declared in <unistd.h>, so it should be included before using it.

For example when trying to build gengetopt generated code with the LSB SDK I get errors like:
cmdline.c:483:3: error: 'optarg' undeclared (first use in this function)
cmdline.c:483:3: note: each undeclared identifier is reported only once for each function it appears in
cmdline.c:484:3: error: 'optind' undeclared (first use in this function)
cmdline.c:485:3: error: 'opterr' undeclared (first use in this function)
cmdline.c:486:3: error: 'optopt' undeclared (first use in this function)

Adding #include <unistd.h> to config.h works around the problem in an ugly way, but it would be better if gengetopt's generated code had that include already. (or if I could add that #include to .ggo to instruct gengetopt to include it for me).

Thanks.