memcpy和memmove的区别.docVIP

memcpy（）和memmove（）都是C语言中的库函数，在头文件string.h中，其原型分别如下： ? DEvoid?*memcpy(void?*dst,?const?void?*src,?size_t?count);void?*memmove(void?*dst,?const?void?*src,?size_t?count);DE ? 它们都是从src所指向的内存中复制count个字节到dst所指内存中，并返回dst的值。当源内存区域和目标内存区域无交叉时，两者的结果是一样的，但如果有交叉呢？先看下图： ? 图的上半部分为源内存区域在目标内存区域右边，下半部分为源内存区域在目标区域左边，源内存区域和目标内存区域都有交叉。 memcpy（）是从src的起始部分开始复制，所以虽然第一种情况下没有问题，但如果遇到第二种情况，则会发生错误，如图所示，后两个字节在被复制前已经被覆盖掉了。而memmove（）则由于采用了不同的复制机制，所以可以正确处理第二种情况。 VS.NET2003中所附源码如下（有删）： DEvoid?*?__cdecl?memcpy?(void?*?dst,?const?void?*?src,?size_t?count){????????void?*?ret?=?dst;????????/*?????????* copy from lower addresses to higher addresses?????????*/????????while?(count--)?{????????????????*(char?*)dst?=?*(char?*)src;????????????????dst?=?(char?*)dst?+?1;????????????????src?=?(char?*)src?+?1;????????}????????return(ret);}DE DEvoid?*?__cdecl?memmove?(void?*?dst,?const?void?*?src,?size_t?count){????????void?*?ret?=?dst;????????if?(dst?=?src?||?(char?*)dst?=?((char?*)src?+?count))?{????????????????/*?????????????????* Non-Overlapping Buffers?????????????????* copy from lower addresses to higher addresses?????????????????*/????????????????while?(count--)?{????????????????????????*(char?*)dst?=?*(char?*)src;????????????????????????dst?=?(char?*)dst?+?1;????????????????????????src?=?(char?*)src?+?1;????????????????}????????}????????else?{????????????????/*?????????????????* Overlapping Buffers?????????????????* copy from higher addresses to lower addresses?????????????????*/????????????????dst?=?(char?*)dst?+?count?-?1;????????????????src?=?(char?*)src?+?count?-?1;????????????????while?(count--)?{????????????????????????*(char?*)dst?=?*(char?*)src;????????????????????????dst?=?(char?*)dst?-?1;????????????????????????src?=?(char?*)src?-?1;????????????????}????????}????????return(ret);}DE