gnulib/doc/posix-functions/realloc.texi

@node realloc
@section @code{realloc}
@findex realloc

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

Gnulib module: realloc-posix

Portability problems fixed by Gnulib:
@itemize
@item
Upon failure, the function does not set @code{errno} to @code{ENOMEM} on
some platforms:
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-gnu} that substitutes a
@code{realloc} implementation that behaves more like the glibc implementation.