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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
In 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
Er 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 .
Pp
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?)
For this reason
Nx
decided to go with an alternative implementation, and created
Xr reallocarr 3 .

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