通过这个例子我们可以清晰地认识到类什么时候创建临时变量，什么时候消除临时变量，更好地理解拷贝构造函数和一般构造函数以及赋值函数的区别。-Through this example we can clearly recognize the category when creating temporary variables, when the elimination of temporary variables to better understand the copy constructor an