xfree86 man page for memcpy

MEMCPY(3)						     Linux Programmer's Manual							 MEMCPY(3)

NAME
       memcpy - copy memory area

SYNOPSIS
       #include <string.h>

       void *memcpy(void *dest, const void *src, size_t n);

DESCRIPTION
       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.

RETURN VALUE
       The memcpy() function returns a pointer to dest.

ATTRIBUTES
       For an explanation of the terms used in this section, see attributes(7).

       +----------+---------------+---------+
       |Interface | Attribute	  | Value   |
       +----------+---------------+---------+
       |memcpy()  | Thread safety | MT-Safe |
       +----------+---------------+---------+
CONFORMING TO
       POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

NOTES
       Failure to observe the requirement that the memory areas do not overlap has been the source of significant bugs.  (POSIX and  the  C  stan-
       dards  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  implementa-
       tion, 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 mem-
       cpy()  implementation that safely handles the overlapping buffers case (by providing an "older" memcpy() implementation that was aliased to
       memmove(3)).

SEE ALSO
       bcopy(3), bstring(3), memccpy(3), memmove(3), mempcpy(3), strcpy(3), strncpy(3), wmemcpy(3)

COLOPHON
       This page is part of release 4.15 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/.

								    2017-09-15								 MEMCPY(3)