@section @code{realloc}
@findex realloc
-POSIX specification: @url{http://www.opengroup.org/onlinepubs/9699919799/functions/realloc.html}
+POSIX specification:@* @url{http://www.opengroup.org/onlinepubs/9699919799/functions/realloc.html}
Gnulib module: realloc-posix
@item
Upon failure, the function does not set @code{errno} to @code{ENOMEM} on
some platforms:
-mingw.
+mingw, MSVC 9.
@end itemize
Portability problems not fixed by Gnulib:
@itemize
+@item
+It is not portable to call @code{realloc} with a size of 0. With a
+NULL pointer argument, this is the same ambiguity as @code{malloc (0)}
+on whether a unique zero-size object is created. With a non-NULL
+pointer argument, C99 requires that if @code{realloc (p, 0)} returns
+@code{NULL} then @code{p} is still valid. Among implementations that
+obey C99, behavior varies on whether @code{realloc (p, 0)} always
+fails and leaves @code{p} valid, or usually succeeds and returns a
+unique zero-size object; either way, a program not suspecting these
+semantics will leak memory (either the still-valid @code{p}, or the
+non-NULL return value). Meanwhile, several implementations violate
+C99, by always calling @code{free (p)} but returning NULL:
+glibc, Cygwin
@end itemize
-Extension: Gnulib provides a module @samp{realloc} that substitutes a
+Extension: Gnulib provides a module @samp{realloc-gnu} that substitutes a
@code{realloc} implementation that behaves more like the glibc implementation.