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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  real  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)).

SEE ALSO

   bcopy(3),  memccpy(3),  memmove(3),  mempcpy(3), strcpy(3), strncpy(3),
   wmemcpy(3)

COLOPHON

   This page is part of release 4.09 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/.

                              2015-07-23                         MEMCPY(3)



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