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.
The
memcpy() function returns a pointer to
dest.
For an explanation of the terms used in this section, see
attributes(7).
Interface |
Attribute |
Value |
memcpy () |
Thread safety |
MT-Safe |
POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
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 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)).
bcopy(3),
bstring(3),
memccpy(3),
memmove(3),
mempcpy(3),
strcpy(3),
strncpy(3),
wmemcpy(3)