2fe8fb192f
There is important information about booting non-ack images in docs/UPDATING. ack/aout-format images can't be built any more, and booting clang/ELF-format ones is a little different. Updating to the new boot monitor is recommended. Changes in this commit: . drop boot monitor -> allowing dropping ack support . facility to copy ELF boot files to /boot so that old boot monitor can still boot fairly easily, see UPDATING . no more ack-format libraries -> single-case libraries . some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases . drop several ack toolchain commands, but not all support commands (e.g. aal is gone but acksize is not yet). . a few libc files moved to netbsd libc dir . new /bin/date as minix date used code in libc/ . test compile fix . harmonize includes . /usr/lib is no longer special: without ack, /usr/lib plays no kind of special bootstrapping role any more and bootstrapping is done exclusively through packages, so releases depend even less on the state of the machine making them now. . rename nbsd_lib* to lib* . reduce mtree
230 lines
5.6 KiB
Groff
230 lines
5.6 KiB
Groff
.\" $NetBSD: malloc.3,v 1.38 2010/05/03 08:23:20 jruoho Exp $
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.\"
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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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.\" @(#)malloc.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD: src/lib/libc/stdlib/malloc.3,v 1.73 2007/06/15 22:32:33 jasone Exp $
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.\"
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.Dd May 3, 2010
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.Dt MALLOC 3
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.Os
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.Sh NAME
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.Nm malloc , calloc , realloc , free
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.Nd general purpose memory allocation functions
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdlib.h
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.Ft void *
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.Fn malloc "size_t size"
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.Ft void *
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.Fn calloc "size_t number" "size_t size"
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.Ft void *
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.Fn realloc "void *ptr" "size_t size"
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.Ft void
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.Fn free "void *ptr"
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.Sh DESCRIPTION
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The
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.Fn malloc
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function allocates
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.Fa size
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bytes of uninitialized memory.
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The allocated space is suitably aligned (after possible pointer coercion)
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for storage of any type of object.
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.Pp
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The
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.Fn calloc
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function allocates space for
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.Fa number
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objects,
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each
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.Fa size
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bytes in length.
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The result is identical to calling
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.Fn malloc
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with an argument of
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.Dq "number * size" ,
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with the exception that the allocated memory is explicitly initialized
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to zero bytes.
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.Pp
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The
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.Fn realloc
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function changes the size of the previously allocated memory referenced by
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.Fa ptr
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to
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.Fa size
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bytes.
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The contents of the memory are unchanged up to the lesser of the new and
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old sizes.
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If the new size is larger,
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the value of the newly allocated portion of the memory is undefined.
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Upon success, the memory referenced by
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.Fa ptr
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is freed and a pointer to the newly allocated memory is returned.
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Note that
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.Fn realloc
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may move the memory allocation, resulting in a different return value than
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.Fa ptr .
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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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the
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.Fn realloc
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function behaves identically to
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.Fn malloc
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for the specified size.
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.Pp
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The
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.Fn free
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function causes the allocated memory referenced by
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.Fa ptr
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to be made available for future allocations.
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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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.Sh RETURN VALUES
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The
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.Fn malloc
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and
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.Fn calloc
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functions return a pointer to the allocated memory if successful; otherwise
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a
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.Dv NULL
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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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The
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.Fn realloc
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function returns a pointer, possibly identical to
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.Fa ptr ,
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to the allocated memory
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if successful; otherwise a
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.Dv NULL
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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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if the error was the result of an allocation failure.
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The
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.Fn realloc
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function always leaves the original buffer intact
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when an error occurs.
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.Pp
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The
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.Fn free
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function returns no value.
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.Sh EXAMPLES
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When using
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.Fn malloc ,
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be careful to avoid the following idiom:
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.Bd -literal -offset indent
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if ((p = malloc(number * size)) == NULL)
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err(EXIT_FAILURE, "malloc");
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.Ed
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.Pp
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The multiplication may lead to an integer overflow.
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To avoid this,
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.Fn calloc
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is recommended.
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.Pp
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If
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.Fn malloc
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must be used, be sure to test for overflow:
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.Bd -literal -offset indent
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if (size && number > SIZE_MAX / size) {
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errno = EOVERFLOW;
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err(EXIT_FAILURE, "allocation");
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}
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.Ed
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.Pp
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When using
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.Fn realloc ,
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one must be careful to avoid the following idiom:
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.Pp
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.Bd -literal -offset indent
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nsize += 50;
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if ((p = realloc(p, nsize)) == 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 it is known that 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 example will also leak 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 ((p2 = realloc(p, newsize)) == NULL) {
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if (p != NULL)
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free(p);
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p = NULL;
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return NULL;
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}
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p = p2;
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size = newsize;
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.Ed
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.Sh SEE ALSO
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.\" .Xr limits 1 ,
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.Xr madvise 2 ,
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.Xr mmap 2 ,
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.Xr sbrk 2 ,
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.Xr alloca 3 ,
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.Xr atexit 3 ,
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.Xr getpagesize 3 ,
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.Xr memory 3 ,
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.Xr posix_memalign 3
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.Pp
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For the implementation details, see
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.Xr jemalloc 3 .
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.Sh STANDARDS
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The
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.Fn malloc ,
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.Fn calloc ,
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.Fn realloc
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and
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.Fn free
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functions conform to
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.St -isoC .
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