NAME

       memcpy - copy memory area

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <string.h>

       void *memcpy(void dest[restrict .n], const void src[restrict .n],
                    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 │
       └─────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       POSIX.1-2001, C89, SVr4, 4.3BSD.

CAVEATS

       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)

Linux man-pages 6.7                                2023-10-31                                          memcpy(3)