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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
MEMCPY(3) Linux Programmer's Manual MEMCPY(3)
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)
This page is part of release 4.12 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/.
2017-03-13 MEMCPY(3)
Pages that refer to this page: bcopy(3), bstring(3), CPU_SET(3), memccpy(3), memmove(3), mempcpy(3), stpcpy(3), strcat(3), strcpy(3), wmemcpy(3), feature_test_macros(7), signal-safety(7)