NAME

       memcpy - copy memory area

SYNOPSIS

       #include <string.h>

       void *memcpy(void *restrict dest, const void *restrict 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  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),  bstring(3),  memccpy(3),   memmove(3),   mempcpy(3),   strcpy(3),   strncpy(3),
       wmemcpy(3)

COLOPHON

       This  page  is  part of release 5.13 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/.

                                            2021-03-22                                  MEMCPY(3)