reallocarray.3 revision 1.5 $NetBSD: reallocarray.3,v 1.5 2022/10/28 09:43:59 wiz Exp $
Copyright (c) 2015 The NetBSD Foundation, Inc.
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.Dd September 9, 2022 .Dt REALLOCARRAY 3 .Os .Sh NAME .Nm reallocarray .Nd reallocate memory for an array of elements checking for overflow .Sh SYNOPSIS n stdlib.h .Ft void * .Fo reallocarray .Fa "void *ptr" .Fa "size_t nmemb" .Fa "size_t size" .Fc .Sh DESCRIPTION The .Fn reallocarray function reallocates the pointer .Fa ptr to a size appropriate to handle an allocation of .Fa nmemb elements in an array where each of the array elements is .Fa size bytes using .Xr realloc 3 and making sure that overflow does not happen in the multiplication of .Dq "nmemb * size" . Otherwise it behaves like .Xr realloc 3 . .Sh RETURN VALUES The .Fn reallocarray function will return .Dv NULL if there was overflow or if .Xr realloc 3 failed setting .Va errno to .Dv ENOMEM or preserving the value from .Xr realloc 3 . .Sh SEE ALSO .Xr malloc 3 , .Xr realloc 3 , .Xr reallocarr 3 .Sh STANDARDS
Will be part of POSIX, but isn't yet.
.Sh HISTORY The .Fn reallocarray function first appeared in .Ox 5.6 . .Fn reallocarray was redesigned in .Nx 8 as .Fn reallocarr 3 . Until .Nx 10 , .Nm was available in the .Vt _OPENBSD_SOURCE namespace. .Sh CAVEATS The .Fn reallocarray function was designed to facilitate safe, robust programming and overcome the shortcomings of the .Xr malloc 3 and .Xr realloc 3 functions by centralizing the overflow check in the multiplication of .Fa nmemb and .Fa size .
Copyright (c) 2015 The NetBSD Foundation, Inc.
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.
.Dd September 9, 2022 .Dt REALLOCARRAY 3 .Os .Sh NAME .Nm reallocarray .Nd reallocate memory for an array of elements checking for overflow .Sh SYNOPSIS n stdlib.h .Ft void * .Fo reallocarray .Fa "void *ptr" .Fa "size_t nmemb" .Fa "size_t size" .Fc .Sh DESCRIPTION The .Fn reallocarray function reallocates the pointer .Fa ptr to a size appropriate to handle an allocation of .Fa nmemb elements in an array where each of the array elements is .Fa size bytes using .Xr realloc 3 and making sure that overflow does not happen in the multiplication of .Dq "nmemb * size" . Otherwise it behaves like .Xr realloc 3 . .Sh RETURN VALUES The .Fn reallocarray function will return .Dv NULL if there was overflow or if .Xr realloc 3 failed setting .Va errno to .Dv ENOMEM or preserving the value from .Xr realloc 3 . .Sh SEE ALSO .Xr malloc 3 , .Xr realloc 3 , .Xr reallocarr 3 .Sh STANDARDS
Will be part of POSIX, but isn't yet.
.Sh HISTORY The .Fn reallocarray function first appeared in .Ox 5.6 . .Fn reallocarray was redesigned in .Nx 8 as .Fn reallocarr 3 . Until .Nx 10 , .Nm was available in the .Vt _OPENBSD_SOURCE namespace. .Sh CAVEATS The .Fn reallocarray function was designed to facilitate safe, robust programming and overcome the shortcomings of the .Xr malloc 3 and .Xr realloc 3 functions by centralizing the overflow check in the multiplication of .Fa nmemb and .Fa size .
p There are still portability issues (it does not solve the .Dv 0 sized allocation return ambiguity in the C standard: does .Fn reallocarray return .Dv NULL or a unique pointer to memory that cannot be accessed? Does a .Dv NULL mean that an error occurred, and can someone check .Dv errno in that case to find out what happened?).
p For this reason .Nx decided to go with an alternative implementation, and created .Xr reallocarr 3 .
Indexes created Sun Oct 05 05:09:57 GMT 2025