C++面试--实现一个Memcpy函数

char *strcpy(char *dest,char *src)

{

if (src == NULL || dest == NULL)

return NULL;

char *strdest = dest;

char *strsrc = src;

while ((*strdest++ = *strsrc++) != '\0');

return dest;

}

void *memcpy_(void *memTo,const void *memFrom, size_t size)

{

if (memTo == NULL || memFrom == NULL)

return NULL;

void *res = memTo;

if(memTo > memFrom && (char*)memTo < (char*)memFrom + size)

{//内存有重叠，从高地址开始复制

memTo = (char*)memTo + size - 1;

memFrom = (char*)memFrom + size - 1;

while(size--)

{

*(char*)memTo = *(char*)memFrom;

memTo = (char*)memTo - 1;

memFrom = (char*)memFrom - 1;

}

}