@node getopt
@section @code{getopt}
@findex getopt

POSIX specification: @url{http://www.opengroup.org/onlinepubs/9699919799/functions/getopt.html}

Gnulib module: getopt-posix or getopt-gnu

The module @code{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 @code{<getopt.h>} and a function @code{getopt_long}.

Portability problems fixed by either Gnulib module @code{getopt-posix} or @code{getopt-gnu}:
@itemize
@item
The @code{getopt} function keeps some internal state that cannot be explicitly
reset on some platforms:
mingw.
@item
The value of @code{optind} after a missing required argument is wrong
on some platforms:
MacOS 10.5.
@end itemize

Portability problems fixed by Gnulib module @code{getopt-gnu}:
@itemize
@item
The function @code{getopt} does not support the @samp{+} 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.
@item
The function @code{getopt} does not obey the @samp{-} flag in the options
string when @env{POSIXLY_CORRECT} is set on some platforms:
Cygwin 1.7.0.
@item
The function @code{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.
@item
The function @code{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.
@item
The function @code{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.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
The default behavior of the glibc implementation of @code{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.
@item
The glibc implementation allows a complete reset of the environment,
including re-checking for @env{POSIXLY_CORRECT}, by setting
@code{optind} to 0.  Other implementations provide @code{optreset},
causing a reset by setting it non-zero, although it does not
necessarily re-read @env{POSIXLY_CORRECT}.
@item
Mixing a leading @samp{-} or @samp{+} with a leading @samp{:} in the
optstring argument has inconsistent effects across platforms.
@end itemize