getopt
======

POSIX specification: http://www.opengroup.org/onlinepubs/9699919799/functions/getopt.html

Gnulib module: getopt-posix or getopt-gnu

The module getopt-gnu has support for ``long options'' and for ``options that take optional arguments''.  Compared to the API defined by POSIX, it adds a header file <getopt.h> and a function getopt_long.

Portability problems fixed by either Gnulib module getopt-posix or getopt-gnu:

  * The getopt function keeps some internal state that cannot be explicitly reset on some platforms: mingw.

  * The value of optind after a missing required argument is wrong on some platforms: MacOS 10.5.

Portability problems fixed by Gnulib module getopt-gnu:

  * The function getopt does not support the + flag in the options string on some platforms: MacOS X 10.5, AIX 5.2, HP-UX 11, IRIX 6.5, OSF/1 5.1, Solaris 10.

  * The function getopt does not obey the - flag in the options string when POSIXLY_CORRECT is set on some platforms: Cygwin 1.7.0.

  * The function getopt does not support options with optional arguments on some platforms: MacOS X 10.5, OpenBSD 4.0, AIX 5.2, HP-UX 11, IRIX 6.5, OSF/1 5.1, Solaris 10, Cygwin 1.5.x.

  * The function getopt_long is missing on some platforms: AIX 5.1, HP-UX 11, IRIX 6.5, OSF/1 5.1, Solaris 9, Interix 3.5.

  * The function getopt_long_only is missing on some platforms: MacOS X 10.3, FreeBSD 5.2.1, NetBSD 3.0, AIX 5.1, HP-UX 11, IRIX 6.5, OSF/1 5.1, Solaris 9, mingw, Interix 3.5.

Portability problems not fixed by Gnulib:

  * The default behavior of the glibc implementation of getopt allows mixing option and non-option arguments on the command line in any order. Other implementations, such as the one in Cygwin, enforce strict POSIX compliance: they require that the option arguments precede the non-option arguments.  This is something to watch out in your program's testsuite.

  * The glibc implementation allows a complete reset of the environment, including re-checking for POSIXLY_CORRECT, by setting optind to 0.  Other implementations provide optreset, causing a reset by setting it non-zero, although it does not necessarily re-read POSIXLY_CORRECT.

  * Mixing a leading - or + with a leading : in the optstring argument has inconsistent effects across platforms.