覆盖父类的函数 [英] Overriding parent class's function

问题描述

class classa {
public:
    virtual void foo();
};

class classb : public classa {
public:
     virtual void foo() override;
};


void classa::foo()
{
    std::cout << "foo from a" << std::endl;
}

void classb::foo()
{
    std::cout << "foo from b" << std::endl;
}

int main()
{
    std::vector<classa> stuff; 

    classa a;
    classb b;

    stuff.push_back(a);
    stuff.push_back(b);

    stuff[0].foo();
    stuff[1].foo();


    return 0;
}

我希望上述代码返回

I expected the above code to return

foo from a 
foo from b

$ b b

但它返回 foo从。

我认为这是因为向量存储 classa 但我不知道。
如何获得 b ？

I think this is because the vector stores classa but I am not sure. How can I get classb:foo() to be called by b?

推荐答案

这发生是因为对象切片，你需要保留一个指针向量（最好是智能指针）。

This happens because of object slicing, you'll need to keep a vector of pointers (preferably smart pointers).

我假设 stuff 定义为 std :: vector< classa> stuff; 。

stuff.push_back(b);

被推入向量的对象是 b - 特别是 classa 部分。所有其他类型的信息丢失。要使其按预期工作，您需要：

the object pushed into the vector is a slice of b - particulary the classa part. All other type info is lost. For this to work as expected, you'd need:

std::vector<classa*> stuff;

或类似。现在你的代码的方式，你不能让它工作，因为 stuff [1] 不再是 classb ，但是 classa 。

or similar. The way your code is now, you can't get it to work because stuff[1] is no longer a classb, but a classa.

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