【注】改編自memmove 和 memcpy的區別。原做者若有不爽,請告知!html
memcpy是C語言中的庫函數,在頭文件string.h中,做用是拷貝必定長度的內存的內容,原型分別以下:linux
void *memcpy(void *dest, const void *src, size_t count)
使用memcpy時,有可能會遇到內存重疊的問題:
第一種狀況下,拷貝重疊的區域不會出現問題,內容都可以正確的被拷貝。
第二種狀況下,問題出如今右邊的兩個字節,這兩個字節的原來的內容首先就被覆蓋了,並且沒有保存。因此接下來拷貝的時候,拷貝的是已經被覆蓋的內容,顯然這是有問題的。git
經過memmove能夠避免這一問題。memmove和memcpy實現同樣的功能:內存拷貝。原型以下:github
void *memmove(void *dest, const void *src, size_t count)
如下幾點你須要瞭解:app
有興趣的,能夠看看linux的源碼,實現很簡單,一看就明白。函數
/** * memcpy - Copy one area of memory to another * @dest: Where to copy to * @src: Where to copy from * @count: The size of the area. * * You should not use this function to access IO space, use memcpy_toio() * or memcpy_fromio() instead. */ void *memcpy(void *dest, const void *src, size_t count) { char *tmp = dest; const char *s = src; while (count--) *tmp++ = *s++; return dest; } /** * memmove - Copy one area of memory to another * @dest: Where to copy to * @src: Where to copy from * @count: The size of the area. * * Unlike memcpy(), memmove() copes with overlapping areas. */ void *memmove(void *dest, const void *src, size_t count) { char *tmp; const char *s; if (dest <= src) { tmp = dest; s = src; while (count--) *tmp++ = *s++; } else { tmp = dest; tmp += count; s = src; s += count; while (count--) *--tmp = *--s; } return dest; }