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