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59a21c7fb8
Include BSD versions when functions were introduced. Add mention whether these are BSD extensions.
301 lines
6.6 KiB
Plaintext
301 lines
6.6 KiB
Plaintext
.\"
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.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the American National Standards Committee X3, on Information
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.\" Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $OpenBSD: malloc.3,v 1.126 2019/09/14 13:16:50 otto Exp $
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.\"
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.Dd $Mdocdate: September 14 2019 $
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.Dt reallocarray 3bsd
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.Os
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.Sh NAME
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.Nm reallocarray ,
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.Nm recallocarray ,
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.Nm freezero
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.Nd memory allocation and deallocation
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.Sh LIBRARY
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.ds str-Lb-libbsd Utility functions from BSD systems (libbsd, \-lbsd)
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.ds doc-str-Lb-libbsd \*[str-Lb-libbsd]
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.Lb libbsd
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.Sh SYNOPSIS
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.In stdlib.h
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(See
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.Xr libbsd 7
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for include usage.)
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.Ft void *
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.Fn reallocarray "void *ptr" "size_t nmemb" "size_t size"
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.Ft void *
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.Fn recallocarray "void *ptr" "size_t oldnmemb" "size_t nmemb" "size_t size"
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.Ft void
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.Fn freezero "void *ptr" "size_t size"
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.Sh DESCRIPTION
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.Pp
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Designed for safe allocation of arrays,
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the
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.Fn reallocarray
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function is similar to
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.Fn realloc
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except it operates on
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.Fa nmemb
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members of size
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.Fa size
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and checks for integer overflow in the calculation
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.Fa nmemb
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*
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.Fa size .
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.Pp
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Used for the allocation of memory holding sensitive data,
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the
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.Fn recallocarray
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function guarantees that memory becoming unallocated is explicitly
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.Em discarded ,
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meaning cached free objects are cleared with
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.Xr explicit_bzero 3 .
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.Pp
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The
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.Fn recallocarray
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function is similar to
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.Fn reallocarray
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except it ensures newly allocated memory is cleared similar to
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.Fn calloc .
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If
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.Fa ptr
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is
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.Dv NULL ,
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.Fa oldnmemb
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is ignored and the call is equivalent to
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.Fn calloc .
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If
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.Fa ptr
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is not
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.Dv NULL ,
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.Fa oldnmemb
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must be a value such that
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.Fa oldnmemb
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*
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.Fa size
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is the size of the earlier allocation that returned
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.Fa ptr ,
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otherwise the behavior is undefined.
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The
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.Fn freezero
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function is similar to the
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.Fn free
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function except it ensures memory is explicitly discarded.
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If
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.Fa ptr
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is
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.Dv NULL ,
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no action occurs.
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If
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.Fa ptr
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is not
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.Dv NULL ,
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the
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.Fa size
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argument must be equal to or smaller than the size of the earlier allocation
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that returned
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.Fa ptr .
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.Fn freezero
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guarantees the memory range starting at
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.Fa ptr
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with length
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.Fa size
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is discarded while deallocating the whole object originally allocated.
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.Sh RETURN VALUES
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The
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.Fn reallocarray
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and
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.Fn recallocarray
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functions return a pointer to the allocated space if successful; otherwise,
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a null pointer is returned and
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.Va errno
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is set to
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.Er ENOMEM .
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.Pp
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If multiplying
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.Fa nmemb
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and
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.Fa size
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results in integer overflow,
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.Fn reallocarray
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and
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.Fn recallocarray
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return
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.Dv NULL
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and set
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.Va errno
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to
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.Er ENOMEM .
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.Pp
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If
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.Fa ptr
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is not
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.Dv NULL
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and multiplying
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.Fa oldnmemb
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and
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.Fa size
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results in integer overflow
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.Fn recallocarray
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returns
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.Dv NULL
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and sets
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.Va errno
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to
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.Er EINVAL .
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.Sh IDIOMS
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Consider
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.Fn calloc
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or the extensions
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.Fn reallocarray
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and
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.Fn recallocarray
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when there is multiplication in the
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.Fa size
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argument of
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.Fn malloc
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or
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.Fn realloc .
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For example, avoid this common idiom as it may lead to integer overflow:
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.Bd -literal -offset indent
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if ((p = malloc(num * size)) == NULL)
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err(1, NULL);
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.Ed
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.Pp
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A drop-in replacement is
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.Fn reallocarray :
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.Bd -literal -offset indent
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if ((p = reallocarray(NULL, num, size)) == NULL)
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err(1, NULL);
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.Ed
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.Pp
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Alternatively,
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.Fn calloc
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may be used at the cost of initialization overhead.
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.Pp
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When using
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.Fn realloc ,
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be careful to avoid the following idiom:
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.Bd -literal -offset indent
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size += 50;
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if ((p = realloc(p, size)) == NULL)
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return (NULL);
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.Ed
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.Pp
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Do not adjust the variable describing how much memory has been allocated
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until the allocation has been successful.
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This can cause aberrant program behavior if the incorrect size value is used.
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In most cases, the above sample will also result in a leak of memory.
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As stated earlier, a return value of
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.Dv NULL
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indicates that the old object still remains allocated.
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Better code looks like this:
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.Bd -literal -offset indent
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newsize = size + 50;
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if ((newp = realloc(p, newsize)) == NULL) {
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free(p);
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p = NULL;
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size = 0;
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return (NULL);
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}
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p = newp;
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size = newsize;
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.Ed
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.Pp
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As with
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.Fn malloc ,
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it is important to ensure the new size value will not overflow;
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i.e. avoid allocations like the following:
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.Bd -literal -offset indent
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if ((newp = realloc(p, num * size)) == NULL) {
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...
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.Ed
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.Pp
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Instead, use
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.Fn reallocarray :
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.Bd -literal -offset indent
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if ((newp = reallocarray(p, num, size)) == NULL) {
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...
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.Ed
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.Pp
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Calling
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.Fn realloc
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with a
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.Dv NULL
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.Fa ptr
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is equivalent to calling
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.Fn malloc .
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Instead of this idiom:
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.Bd -literal -offset indent
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if (p == NULL)
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newp = malloc(newsize);
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else
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newp = realloc(p, newsize);
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.Ed
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.Pp
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Use the following:
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.Bd -literal -offset indent
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newp = realloc(p, newsize);
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.Ed
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.Pp
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The
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.Fn recallocarray
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function should be used for resizing objects containing sensitive data like
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keys.
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To avoid leaking information,
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it guarantees memory is cleared before placing it on the internal free list.
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Deallocation of such an object should be done by calling
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.Fn freezero .
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.Sh SEE ALSO
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.Xr malloc 3 ,
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.Xr calloc 3 ,
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.Xr alloca 3
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.Sh HISTORY
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The
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.Fn reallocarray
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function appeared in
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.Ox 5.6 ,
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.Dx 5.5
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and glibc 2.26.
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.Pp
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The
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.Fn recallocarray
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function appeared in
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.Ox 6.1
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and
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.Dx 5.5 .
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The
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.Fn freezero
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function appeared in
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.Ox 6.2
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and
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.Dx 5.5 .
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