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 at-
tributes(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 standards
are explicit that employing memcpy() with overlapping areas produces
undefined behavior.) Most notably, in glibc 2.13 a performance opti-
mization 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 per-
formed 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
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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)