1memcpy(3)                  Library Functions Manual                  memcpy(3)
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NAME

6       memcpy - copy memory area
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LIBRARY

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <string.h>
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14       void *memcpy(void dest[restrict .n], const void src[restrict .n],
15                    size_t n);
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DESCRIPTION

18       The  memcpy()  function  copies  n bytes from memory area src to memory
19       area dest.  The memory areas must not overlap.  Use memmove(3)  if  the
20       memory areas do overlap.
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RETURN VALUE

23       The memcpy() function returns a pointer to dest.
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ATTRIBUTES

26       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
27       tributes(7).
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29       ┌────────────────────────────────────────────┬───────────────┬─────────┐
30       │Interface                                   │ Attribute     │ Value   │
31       ├────────────────────────────────────────────┼───────────────┼─────────┤
32       │memcpy()                                    │ Thread safety │ MT-Safe │
33       └────────────────────────────────────────────┴───────────────┴─────────┘
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STANDARDS

36       C11, POSIX.1-2008.
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HISTORY

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

42       Failure to observe the requirement that the memory areas do not overlap
43       has  been  the  source of significant bugs.  (POSIX and the C standards
44       are explicit that employing memcpy() with  overlapping  areas  produces
45       undefined  behavior.)   Most  notably,  in  glibc  2.13  a  performance
46       optimization of memcpy() on some platforms (including x86-64)  included
47       changing the order in which bytes were copied from src to dest.
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49       This  change  revealed  breakages  in  a  number  of  applications that
50       performed  copying  with  overlapping  areas.    Under   the   previous
51       implementation,   the   order  in  which  the  bytes  were  copied  had
52       fortuitously hidden the bug, which was revealed when the copying  order
53       was  reversed.  In glibc 2.14, a versioned symbol was added so that old
54       binaries (i.e., those linked against glibc versions earlier than  2.14)
55       employed  a memcpy() implementation that safely handles the overlapping
56       buffers case (by providing an "older" memcpy() implementation that  was
57       aliased to memmove(3)).
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SEE ALSO

60       bcopy(3),  bstring(3),  memccpy(3),  memmove(3), mempcpy(3), strcpy(3),
61       strncpy(3), wmemcpy(3)
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65Linux man-pages 6.05              2023-07-20                         memcpy(3)
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