cid 2af875d3a4962bf84bc7ec1a47b028d53f7ce0b9ea9ede308ae07d032bc65d6a · original · open access · via man
Title: memcpy(3) - Linux manual page Authors: Venue: man Year: 2008 Canonical: man:man3/memcpy.3 URL: https://man7.org/linux/man-pages/man3/memcpy.3.html Collector: man OA: true ABSTRACT memcpy(3) - Linux manual page man7.org Linux man-pages Linux/UNIX system programming training memcpy(3) — Linux manual page NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | STANDARDS | HISTORY | CAVEATS | SEE ALSO | COLOPHON memcpy(3) Library Functions Manual memcpy(3) NAME top memcpy - memory copy LIBRARY top Standard C library (libc, -lc) SYNOPSIS top #include // see memory.h(3head) void *memcpy(size_t n; 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) 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). ┌──────────────────────────────────────┬───────────────┬─────────┐ │ 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)). SEE ALSO top memory.h(3head), memmove(3), mempcpy(3), wmemcpy(3) COLOPHON top This page is part of the man-pages (Linux kernel and C library user-space interface documentation) project. Information about the project can be found at ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report for this manual page, see ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩. This page was obtained from the tarball man-pages-6.19.tar.gz fetched from ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on 2026-09-09. If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up- to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which is not part of the original manual page), send a mail to man-pages@man7.org Linux man-pages 6.19 2026-08-10 memcpy(3) Pages that refer to this page: bcopy(3), cmsg(3), CPU_SET(3), memmove(3), memory.h(3head), mempcpy(3), size_t(3type), void(3type), wmemcpy(3), feature_test_macros(7), signal-safety(7), string_copying(7) HTML rendering created 2026-09-09 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH.