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.\" Copyright (c) 1980, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the American National Standards Committee X3, on Information
.\" Processing Systems.
.\"
.\" 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 REGENTS 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 REGENTS 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.
.\"
.\" $FreeBSD$
.\"
.Dd May 1, 2015
.Dt REALLOCARRAY 3
.Os
.Sh NAME
.Nm reallocarray
.Nd memory reallocation function
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft void *
.Fn reallocarray "void *ptr" "size_t nmemb" "size_t size"
.Sh DESCRIPTION
The
.Fn reallocarray
function is similar to the
.Fn realloc
function
except it operates on
.Fa nmemb
members of size
.Fa size
and checks for integer overflow in the calculation
.Fa nmemb
*
.Fa size .
.Sh RETURN VALUES
The
.Fn reallocarray
function returns a pointer to the allocated space; otherwise, a
.Dv NULL
pointer is returned and
.Va errno
is set to
.Er ENOMEM .
.Sh EXAMPLES
Consider
.Fn reallocarray
when there is multiplication in the
.Fa size
argument of
.Fn malloc
or
.Fn realloc .
For example, avoid this common idiom as it may lead to integer overflow:
.Bd -literal -offset indent
if ((p = malloc(num * size)) == NULL)
err(1, "malloc");
.Ed
.Pp
A drop-in replacement is the
.Ox
extension
.Fn reallocarray :
.Bd -literal -offset indent
if ((p = reallocarray(NULL, num, size)) == NULL)
err(1, "reallocarray");
.Ed
.Pp
When using
.Fn realloc ,
be careful to avoid the following idiom:
.Bd -literal -offset indent
size += 50;
if ((p = realloc(p, size)) == NULL)
return (NULL);
.Ed
.Pp
Do not adjust the variable describing how much memory has been allocated
until the allocation has been successful.
This can cause aberrant program behavior if the incorrect size value is used.
In most cases, the above sample will also result in a leak of memory.
As stated earlier, a return value of
.Dv NULL
indicates that the old object still remains allocated.
Better code looks like this:
.Bd -literal -offset indent
newsize = size + 50;
if ((newp = realloc(p, newsize)) == NULL) {
free(p);
p = NULL;
size = 0;
return (NULL);
}
p = newp;
size = newsize;
.Ed
.Pp
As with
.Fn malloc ,
it is important to ensure the new size value will not overflow;
i.e. avoid allocations like the following:
.Bd -literal -offset indent
if ((newp = realloc(p, num * size)) == NULL) {
...
.Ed
.Pp
Instead, use
.Fn reallocarray :
.Bd -literal -offset indent
if ((newp = reallocarray(p, num, size)) == NULL) {
...
.Ed
.Sh SEE ALSO
.Xr realloc 3
.Sh HISTORY
The
.Fn reallocarray
function first appeared in
.Ox 5.6
and
.Fx 11.0 .
|
