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
       attributes(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
       This page is part of release 4.16 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/.



                                  2017-09-15                         MEMCPY(3)