C++ 实现memcpy

/**
 * @Method: Memcpy
 * @Access: public 
 * @Return: void *
 * @Param : dst - 目的起始地址
 * @Param : src - 源起始地址
 * @Param : len - 所要拷贝空间大小Byte
 * @Brief : 内存拷贝，实现了内存重叠和非重叠的拷贝
 * @Date  : 2015-8-20 FengKang
 */
void *Memcpy(void *dst, const void *src, size_t len)
{
    if(NULL == dst || NULL == src)
    {
        return NULL;
    }

    void *ret = dst;

    if(dst <= src || (char *)dst >= (char *)src + len)
    {
        while(len--)
        {
            *(char *)dst = *(char *)src;
            dst = (char *)dst + 1;
            src = (char *)src + 1;
        }
    }
    else
    {
        src = (char *)src + len - 1;
        dst = (char *)dst + len - 1;
        while(len--)
        {
            *(char *)dst = *(char *)src;
            dst = (char *)dst - 1;
            src = (char *)src - 1;
        }
    }
    return ret;
}