1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" the American National Standards Committee X3, on Information 6.\" Processing Systems. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 17.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 18.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 21.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27.\" SUCH DAMAGE. 28.\" 29.\" $FreeBSD$ 30.\" 31.Dd May 1, 2015 32.Dt REALLOCARRAY 3 33.Os 34.Sh NAME 35.Nm reallocarray 36.Nd memory reallocation function 37.Sh LIBRARY 38.Lb libc 39.Sh SYNOPSIS 40.In stdlib.h 41.Ft void * 42.Fn reallocarray "void *ptr" "size_t nmemb" "size_t size" 43.Sh DESCRIPTION 44The 45.Fn reallocarray 46function is similar to the 47.Fn realloc 48function 49except it operates on 50.Fa nmemb 51members of size 52.Fa size 53and checks for integer overflow in the calculation 54.Fa nmemb 55* 56.Fa size . 57.Sh RETURN VALUES 58The 59.Fn reallocarray 60function returns a pointer to the allocated space; otherwise, a 61.Dv NULL 62pointer is returned and 63.Va errno 64is set to 65.Er ENOMEM . 66.Sh EXAMPLES 67Consider 68.Fn reallocarray 69when there is multiplication in the 70.Fa size 71argument of 72.Fn malloc 73or 74.Fn realloc . 75For example, avoid this common idiom as it may lead to integer overflow: 76.Bd -literal -offset indent 77if ((p = malloc(num * size)) == NULL) 78 err(1, "malloc"); 79.Ed 80.Pp 81A drop-in replacement is the 82.Ox 83extension 84.Fn reallocarray : 85.Bd -literal -offset indent 86if ((p = reallocarray(NULL, num, size)) == NULL) 87 err(1, "reallocarray"); 88.Ed 89.Pp 90When using 91.Fn realloc , 92be careful to avoid the following idiom: 93.Bd -literal -offset indent 94size += 50; 95if ((p = realloc(p, size)) == NULL) 96 return (NULL); 97.Ed 98.Pp 99Do not adjust the variable describing how much memory has been allocated 100until the allocation has been successful. 101This can cause aberrant program behavior if the incorrect size value is used. 102In most cases, the above sample will also result in a leak of memory. 103As stated earlier, a return value of 104.Dv NULL 105indicates that the old object still remains allocated. 106Better code looks like this: 107.Bd -literal -offset indent 108newsize = size + 50; 109if ((newp = realloc(p, newsize)) == NULL) { 110 free(p); 111 p = NULL; 112 size = 0; 113 return (NULL); 114} 115p = newp; 116size = newsize; 117.Ed 118.Pp 119As with 120.Fn malloc , 121it is important to ensure the new size value will not overflow; 122i.e. avoid allocations like the following: 123.Bd -literal -offset indent 124if ((newp = realloc(p, num * size)) == NULL) { 125 ... 126.Ed 127.Pp 128Instead, use 129.Fn reallocarray : 130.Bd -literal -offset indent 131if ((newp = reallocarray(p, num, size)) == NULL) { 132 ... 133.Ed 134.Sh SEE ALSO 135.Xr realloc 3 136.Sh HISTORY 137The 138.Fn reallocarray 139function first appeared in 140.Ox 5.6 141and 142.Fx 11.0 . 143