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 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)).
SEE ALSO
bcopy(3), memccpy(3), memmove(3), mempcpy(3), strcpy(3), strncpy(3),
wmemcpy(3)
COLOPHON
This page is part of release 4.09 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/.
2015-07-23 MEMCPY(3)
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