Section (3) memcpy
memcpy — copy memory area
|const void *src,|
memcpy() function copies
n bytes from memory
src to memory
dest. The memory
areas must not overlap. Use memmove(3) if the memory
areas do overlap.
For an explanation of the terms used in this section, see attributes(7).
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
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
that was aliased to memmove(3)).
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Linux libc source code
Lewine_zsingle_quotesz_s _POSIX Programmer_zsingle_quotesz_s Guide_ (O_zsingle_quotesz_Reilly & Associates, 1991)
386BSD man pages
Modified Sun Jul 25 10:41:09 1993 by Rik Faith (faithcs.unc.edu)