1.\" Copyright (c) 2015 OpenBSD 2.\" 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 46except it operates on 47.Fa nmemb 48members of size 49.Fa size 50and checks for integer overflow in the calculation 51.Fa nmemb 52* 53.Fa size . 54.Sh RETURN VALUES 55.Fn reallocarray 56return a pointer to the allocated space; otherwise, a 57.Dv NULL 58pointer is returned and 59.Va errno 60is set to 61.Er ENOMEM . 62.Sh EXAMPLES 63Consider 64.Fn reallocarray 65when there is multiplication in the 66.Fa size 67argument of 68.Fn malloc 69or 70.Fn realloc . 71For example, avoid this common idiom as it may lead to integer overflow: 72.Bd -literal -offset indent 73if ((p = malloc(num * size)) == NULL) 74 err(1, "malloc"); 75.Ed 76.Pp 77A drop-in replacement is the 78.Ox 79extension 80.Fn reallocarray : 81.Bd -literal -offset indent 82if ((p = reallocarray(NULL, num, size)) == NULL) 83 err(1, "reallocarray"); 84.Ed 85.Pp 86When using 87.Fn realloc , 88be careful to avoid the following idiom: 89.Bd -literal -offset indent 90size += 50; 91if ((p = realloc(p, size)) == NULL) 92 return (NULL); 93.Ed 94.Pp 95Do not adjust the variable describing how much memory has been allocated 96until the allocation has been successful. 97This can cause aberrant program behavior if the incorrect size value is used. 98In most cases, the above sample will also result in a leak of memory. 99As stated earlier, a return value of 100.Dv NULL 101indicates that the old object still remains allocated. 102Better code looks like this: 103.Bd -literal -offset indent 104newsize = size + 50; 105if ((newp = realloc(p, newsize)) == NULL) { 106 free(p); 107 p = NULL; 108 size = 0; 109 return (NULL); 110} 111p = newp; 112size = newsize; 113.Ed 114.Pp 115As with 116.Fn malloc , 117it is important to ensure the new size value will not overflow; 118i.e. avoid allocations like the following: 119.Bd -literal -offset indent 120if ((newp = realloc(p, num * size)) == NULL) { 121 ... 122.Ed 123.Pp 124Instead, use 125.Fn reallocarray : 126.Bd -literal -offset indent 127if ((newp = reallocarray(p, num, size)) == NULL) { 128 ... 129.Ed 130.Sh SEE ALSO 131.Xr realloc 3 132.Sh HISTORY 133The 134.Fn reallocf 135function first appeared in 136.Ox 5.6 . 137