memcpy — copy memory area
#include <string.h>
void
*memcpy( |
void *dest, |
| const void *src, | |
size_t n); |
The memcpy() function copies
n bytes from memory
area src to memory
area dest. The memory
areas must not overlap. Use memmove(3) if the memory
areas do overlap.
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
memcpy() |
Thread safety | MT-Safe |
Failure to observe the requirement that the memory areas
do not overlap has been the source of real bugs. (POSIX and
the C standards are explicit that employing memcpy() with overlapping areas produces
undefined behavior.) Most notably, in glibc 2.13 a
performance optimization of memcpy() on some platforms (including
x86-64) included changing the order in which bytes were
copied from src to
dest.
This change revealed breakages in a number of applications
that performed copying with overlapping areas. Under the
previous implementation, the order in which the bytes were
copied had fortuitously hidden the bug, which was revealed
when the copying order was reversed. In glibc 2.14, a
versioned symbol was added so that old binaries (i.e., those
linked against glibc versions earlier than 2.14) employed a
memcpy() implementation that
safely handles the overlapping buffers case (by providing an
"older" memcpy() implementation
that was aliased to memmove(3)).
This page is part of release 4.07 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
|
Copyright 1993 David Metcalfe (davidprism.demon.co.uk) and Copyright 2015 Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END References consulted: Linux libc source code Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) 386BSD man pages Modified Sun Jul 25 10:41:09 1993 by Rik Faith (faithcs.unc.edu) |