memcpy(3)                  Library Functions Manual                  memcpy(3)

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)