为什么以及如何重载操作符<<用于打印 [英] Why and how to overload operator<< for printing

问题描述

我写了一个程序来实现堆栈。我有一个显示功能。

I have written a program for implementation of stack. And I have one display function in it.

这是我第一次写显示函数的方式：

This is how I wrote display function at first:

template <class t>
void Mystack<t>::display()
{
    for (int i = 0; i <= top; i++)
    {
        std::cout << input[i] << " ";
    }
}

然后我建议开发者写一个显示函数更通用。所以我写显示函数为：

Then I was suggested by developers to write a display function to be more generic. So I wrote display function as:

template <class T>
void Mystack<T>::display(std::ostream &os) const         
{
    for (int i = 0; i <= top; i++)
    {
        os << input[i] << " ";
    }
}

根据我的理解，写上述函数的好处是

As per my understanding the benefit of writing above function is that now I have a generic display function which I can use to display data to console or to a file too.

问题1 ：是我的一个显示功能，我可以用来显示数据到控制台或文件。理解正确吗？

Question 1: Is my understanding correct?

现在，另一个建议是写函数：

Now another suggestion is to write function something like:

template <typename T>
friend std::ostream& operator<<(std::ostream& s, Mystack<T> const& d) {
    d.display(s);
    return s;
}

问题2 ：以上显示功能？

推荐答案

对于问题1，你的理解是正确的，但是实际改进来自问题2的写作建议：

For question 1, your understanding is correct, but the real improvement comes from question 2's suggestion of writing:

template <typename T>
friend std::ostream& operator<<(std::ostream&, Mystack<T> const& );

这将允许任何人以类似于流式传输的方式流式传输您的类型的对象： p>

That will let anybody stream objects of your type in the same way they would stream anything else:

std::cout << "Hi, my stack is " << stack << ", it has size " << stack.size();

到任何他们想要的讯息串：

to any stream they want:

some_file << "Result of computation is: " << stack;
std::cerr << "Error, invalid stack: " << stack << ", expected: " << some_other_thing;

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