我如何看到地址和值C ++类之间的区别? [英] How can i see the difference between address and value c++ class?

问题描述

我在指针和参考理解方面有问题.我有以下代码段:

I have a problem in pointers and reference understanding. I have the following snippet:

class U
{
protected:
    int m;
public:
    U(int m = 0) : m(m) {}
    virtual void f() { cout << "U::f() @ m = " << m << endl; }
};

class V : public U
{
    int n;
public:
    V(int m, int n) : U(m), n(n) {}
    void f() { cout << "V::f() @ m = " << m << ", n = " << n << endl; }
};

int main() {
    V v1(1, 1), v2(2, 2);
    v1.f();
    v2.f();
    U* u = &v1;
    *u = v2;
    v1.f();
    v2.f();
}

我运行此命令，输出为:

I run this and the output is:

V::f() @ m = 1, n = 1
V::f() @ m = 2, n = 2
V::f() @ m = 2, n = 1
V::f() @ m = 2, n = 2

我不明白输出的第三行: V :: f()@ m = 2，n = 1 .为什么将 m 更改为 2 ?

I don't understand the third line of output: V::f() @ m = 2, n = 1. Why m is changed to 2?

推荐答案

*u=v2;

这不会使 u 指向 v2 .它将 v2 分配给 u 指向的对象的 U 子对象，即 U 部分的 v1 .这是因为 * u 是 U 对象.

This doesn't make u point to v2. It assigns v2 to the U sub-object of the object that u points to, i.e. to the U part of v1. This is because *u is a U object.

这篇关于我如何看到地址和值C ++类之间的区别?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！