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Diffstat (limited to 'lib/libc/stdlib/reallocarray.3')
| -rw-r--r-- | lib/libc/stdlib/reallocarray.3 | 142 |
1 files changed, 142 insertions, 0 deletions
diff --git a/lib/libc/stdlib/reallocarray.3 b/lib/libc/stdlib/reallocarray.3 new file mode 100644 index 0000000..8e714f4 --- /dev/null +++ b/lib/libc/stdlib/reallocarray.3 @@ -0,0 +1,142 @@ +.\" 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 . |
