memcpy(3)		    Library Functions Manual		       memcpy(3)

NAME
     memcpy - copy memory area

LIBRARY
     Standard C library (libc, -lc)

SYNOPSIS
     #include <string.h>

     void *memcpy(size_t n;
		  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 ar-
     eas 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).
     allbox; lbx lb lb l l l.  Interface Attribute Value T{ memcpy() T}	  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 ex-
     plicit that employing memcpy() with overlapping  areas  produces  undefined
     behavior.)	  Most notably, in glibc 2.13 a performance optimization of mem-
     cpy() 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 or-
     der 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 ver-
     sioned 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"  mem-
     cpy() 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 6.18		   2026-02-08			       memcpy(3)