@node reallocarray
@subsection @code{reallocarray}
@findex reallocarray

POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9799919799/functions/reallocarray.html}

Documentation:
@itemize
@item
@ifinfo
@ref{Changing Block Size,,Changing the Size of a Block,libc},
@end ifinfo
@ifnotinfo
@url{https://www.gnu.org/software/libc/manual/html_node/Changing-Block-Size.html},
@end ifnotinfo
@item
@uref{https://www.kernel.org/doc/man-pages/online/pages/man3/reallocarray.3.html,,man reallocarray}.
@end itemize

Gnulib module: reallocarray
@mindex reallocarray

Portability problems fixed by Gnulib:
@itemize
@item
This function is missing on many platforms:
glibc 2.25, macOS 14, FreeBSD 10, NetBSD 7, OpenBSD 5.5, Minix 3.3.0, AIX 7.2, HP-UX 11, Solaris 11.4, Cygwin 1.7.x, mingw, MSVC 14, Android 9.0.

@item
On some platforms, when the function fails it might set @code{errno}
to @code{EAGAIN} instead of to @code{ENOMEM}. Although POSIX allows
@code{EAGAIN}, the @code{reallocarray} module insists on @code{ENOMEM}
which also conforms to POSIX and is GNU-compatible:
Solaris 11.4.

@item
On some platforms, @code{reallocarray (p, n, s)} can succeed even if
multiplying @code{n} by @code{s} would exceed @code{PTRDIFF_MAX},
which can lead to undefined behavior later:
FreeBSD 13, NetBSD 9, OpenBSD 6, musl 1.2.

@item
It is not portable to call
@code{reallocarray (p, n, s)} when either @code{n} or @code{s} is zero,
as @code{reallocarray} has the same issues with zero sizes
that @code{realloc} does.  @xref{realloc}.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
When not growing an already-allocated region,
@code{reallocarray}, like @code{realloc}, can fail and return a null pointer:
glibc 2.40 and probably other platforms.
@end itemize
