memcpy

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)