memcpy()函数，memmove()函数

memcpy()函数，memmove()函数的实现。

//直接搬移dest的前n个字符
void* memcpy(void* dest, const void* src, size_t n)
{
    assert(dest != NULL && src != NULL);
    char* d = (char*)dest;
    const char* s = (const char*)src;
    while (n--)
        *d++ = *s++;
    return dest;
}



void *memmove(void *dest, const void *src, size_t n)
{
    assert(dest != NULL && src != NULL);
    char *d = (char *)dest;
    const char* s = (const char*)src;
    if (s > d)                 //判断是否会发生覆盖的情况
    {
        while (n--)
            *d++ = *s++;
    }
    else if (s < d)           //覆盖了就从后面开始拷贝
    {
        d = d + n - 1;
        s = s + n - 1;
        while (n--)
            *d-- = *s--;
    }
    return dest;
}