memcpy
Section: C Library Functions (3)
Updated: 202-0-08
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NAME
memcpy - copy memory area
LIBRARY
Standard C library
(
libc,~
-lc)
SYNOPSIS
#include <string.h>
void *memcpy(size_t n;
void dest[restrict n], const void src[restrict n],
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 | M-Safe
|
STANDARDS
C11, POSIX.-2008.
HISTORY
POSIX.-2001, C89, SVr4, 4.3BSD.
CAVEATS
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 x8-64) 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),
bstring(3),
memccpy(3),
memmove(3),
mempcpy(3),
strcpy(3),
strncpy(3),
wmemcpy(3)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ATTRIBUTES
-
- STANDARDS
-
- HISTORY
-
- CAVEATS
-
- SEE ALSO
-
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