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.Dd May 1, 2015 30.Dt REALLOCARRAY 3 31.Os 32.Sh NAME 33.Nm reallocarray 34.Nd memory reallocation function 35.Sh LIBRARY 36.Lb libc 37.Sh SYNOPSIS 38.In stdlib.h 39.Ft void * 40.Fn reallocarray "void *ptr" "size_t nmemb" "size_t size" 41.Sh DESCRIPTION 42The 43.Fn reallocarray 44function is similar to the 45.Fn realloc 46function 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 56The 57.Fn reallocarray 58function returns a pointer to the allocated space; otherwise, a 59.Dv NULL 60pointer is returned and 61.Va errno 62is set to 63.Er ENOMEM . 64.Sh EXAMPLES 65Consider 66.Fn reallocarray 67when there is multiplication in the 68.Fa size 69argument of 70.Fn malloc 71or 72.Fn realloc . 73For example, avoid this common idiom as it may lead to integer overflow: 74.Bd -literal -offset indent 75if ((p = malloc(num * size)) == NULL) 76 err(1, "malloc"); 77.Ed 78.Pp 79A drop-in replacement is the 80.Ox 81extension 82.Fn reallocarray : 83.Bd -literal -offset indent 84if ((p = reallocarray(NULL, num, size)) == NULL) 85 err(1, "reallocarray"); 86.Ed 87.Pp 88When using 89.Fn realloc , 90be careful to avoid the following idiom: 91.Bd -literal -offset indent 92size += 50; 93if ((p = realloc(p, size)) == NULL) 94 return (NULL); 95.Ed 96.Pp 97Do not adjust the variable describing how much memory has been allocated 98until the allocation has been successful. 99This can cause aberrant program behavior if the incorrect size value is used. 100In most cases, the above sample will also result in a leak of memory. 101As stated earlier, a return value of 102.Dv NULL 103indicates that the old object still remains allocated. 104Better code looks like this: 105.Bd -literal -offset indent 106newsize = size + 50; 107if ((newp = realloc(p, newsize)) == NULL) { 108 free(p); 109 p = NULL; 110 size = 0; 111 return (NULL); 112} 113p = newp; 114size = newsize; 115.Ed 116.Pp 117As with 118.Fn malloc , 119it is important to ensure the new size value will not overflow; 120i.e. avoid allocations like the following: 121.Bd -literal -offset indent 122if ((newp = realloc(p, num * size)) == NULL) { 123 ... 124.Ed 125.Pp 126Instead, use 127.Fn reallocarray : 128.Bd -literal -offset indent 129if ((newp = reallocarray(p, num, size)) == NULL) { 130 ... 131.Ed 132.Sh SEE ALSO 133.Xr realloc 3 134.Sh HISTORY 135The 136.Fn reallocarray 137function first appeared in 138.Ox 5.6 139and 140.Fx 11.0 . 141