memcpy(3) — Linux manual page


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

NAME         top

       memcpy - copy memory area

SYNOPSIS         top

       #include <string.h>

       void *memcpy(void *dest, const void *src, size_t n);

DESCRIPTION         top

       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         top

       The memcpy() function returns a pointer to dest.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface Attribute     Value   │
       │memcpy()  │ Thread safety │ MT-Safe │

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

NOTES         top

       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         top

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

COLOPHON         top

       This page is part of release 5.08 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

                                 2017-09-15                        MEMCPY(3)

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