MEMCPY(3)                                                               Linux Programmer's Manual                                                              MEMCPY(3)

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 over‐
       lap.

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)

                                                                               2021-03-22                                                                      MEMCPY(3)