memcpy和memmove的区别与实现

1、区别：两个函数都是进行n字节内存内容的拷贝，入口参数和返回参数也都一样，可是这两个函数在内部实现上是有一定区别的，这主要是因为dest内存区域和src内存区域可能有一下四种不同的情况，注意count的影响：从图中可以看出，src的内存区域和dest的内存区域相对位置和重叠关系有四种情况，memcpy没有考虑重叠的情况，而memmove考虑到了全部情况，因此memcpy函数的时候可能出现意向不到的结果。这两个函数的实现：*下面两个是错误的实现*void* memcpy(void* dest, void* source, size_t count)    &

2、#160;            void* ret = dest;          /copy from lower address to higher address          while (count-)        &#

3、160;         *dest+ = *source+; /不知道两个指针的类型，不可以这样自加。           return ret;      void* memmove(void* dest, void* source, size_t count) void* ret = dest; if (dest <= source | dest >

4、= (source + count) /Non-Overlapping Buffers /copy from lower addresses to higher addresses while (count -) *dest+ = *source+; else /Overlapping Buffers /copy from higher addresses to lower addresses dest += count - 1; source += count - 1; while (count-) *dest- = *source-; / 情况同上 return ret; *正确的如下*v

5、oid* mymemcpy(void* dest, void* source, size_t count) char *ret = (char *)dest; char *dest_t = ret; char *source_t = (char *)source; while (count-) *dest_t+ = *source_t+; return ret; void *my_memmove(void *dst,const void *src,int count) char *ret; char *dst_t; char *src_t; ret = (char *)dst; if (unsigned char*)dst <= (unsigned char*)src | (unsigned char *)dst >= (unsigned char *)src + count) dst_t = (char *)dst; src_t = (char *)src; while (count-) *dst_t+ = *src_t+; else dst_t = (char *)dst + c