options string when @env{POSIXLY_CORRECT} is set on some platforms:
Cygwin 1.7.0.
@item
+Some implementations fail to reset state, including re-checking
+@env{POSIXLY_CORRECT}, when @code{optind} is set to @samp{0}:
+NetBSD, Cygwin 1.7.0.
+@item
The function @code{getopt_long} does not support options with optional
arguments on some platforms:
MacOS X 10.5, OpenBSD 4.0, AIX 5.2, IRIX 6.5, Solaris 10, Cygwin 1.5.x.
Portability problems not fixed by Gnulib:
@itemize
@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}.
+The glibc extension of using @samp{W;} in the optstring argument to
+allow @code{-W foo} to behave synonymously with @code{--foo} is not
+very reliable, even in glibc.
+@item
+Mixing a leading @samp{-} or @samp{+} with a leading @samp{:} in the
+optstring argument has inconsistent effects across platforms.
@end itemize