memcpy(3) - Linux manual page (original) (raw)

memcpy(3) Library Functions Manual memcpy(3)

NAME top

   memcpy - copy memory area

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#include <string.h>**

   **void *memcpy(void** _dest_**[restrict .**_n_**], const void** _src_**[restrict .**_n_**],**
                **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)](../man3/memmove.3.html) 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
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────────┬───────────────┬─────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├──────────────────────────────────────┼───────────────┼─────────┤
   │ **memcpy**()                             │ Thread safety │ MT-Safe │
   └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS top

   C11, POSIX.1-2008.

HISTORY top

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

CAVEATS 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)](../man3/memmove.3.html)).

SEE ALSO top

   [bcopy(3)](../man3/bcopy.3.html), [bstring(3)](../man3/bstring.3.html), [memccpy(3)](../man3/memccpy.3.html), [memmove(3)](../man3/memmove.3.html), [mempcpy(3)](../man3/mempcpy.3.html),
   [strcpy(3)](../man3/strcpy.3.html), [strncpy(3)](../man3/strncpy.3.html), [wmemcpy(3)](../man3/wmemcpy.3.html)

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Linux man-pages 6.10 2024-07-23 memcpy(3)

Pages that refer to this page:bcopy(3), bstring(3), cmsg(3), CPU_SET(3), memccpy(3), memmove(3), mempcpy(3), size_t(3type), void(3type), wmemcpy(3), feature_test_macros(7), signal-safety(7), string_copying(7)