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


memcpy - メモリー領域をコピーする。


#include <string.h>
void *memcpy(void *dest, const void *src, size_t n);


memcpy() はメモリー領域 src の先頭 n バイトを メモリー領域 dest にコピーする。コピー元の領域と コピー先の領域が重なってはならない。重なっている場合は memmove(3) を使うこと。


memcpy() は dest へのポインターを返す。


この節で使用されている用語の説明については、 attributes(7) を参照。

インターフェース 属性
memcpy() Thread safety MT-Safe


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


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)).


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


この man ページは Linux man-pages プロジェクトのリリース 5.10 の一部である。プロジェクトの説明とバグ報告に関する情報は に書かれている。