相当于Java的toString的C ++？ [英] C++ equivalent of Java's toString?

问题描述

我想控制自定义类对象写入流中的内容，即 cout 。在C ++中有可能吗？在Java中，出于类似的目的，您可以覆盖 toString（）方法。

I'd like to control what is written to a stream, i.e. cout, for an object of a custom class. Is that possible in C++? In Java you could override the toString() method for similar purpose.

推荐答案

在C ++中，您可以为 ostream 和您的自定义类重载 operator<<
$ b

In C++ you can overload operator<< for ostream and your custom class:

class A {
public:
  int i;
};

std::ostream& operator<<(std::ostream &strm, const A &a) {
  return strm << "A(" << a.i << ")";
}

这样，您可以在流上输出类的实例：

This way you can output instances of your class on streams:

A x = ...;
std::cout << x << std::endl;

如果您的操作员<< 想要打印出 A 类的内部并且确实需要访问其私有成员和受保护成员，您还可以将其声明为朋友函数：

In case your operator<< wants to print out internals of class A and really needs access to its private and protected members you could also declare it as a friend function:

class A {
private:
  friend std::ostream& operator<<(std::ostream&, const A&);
  int j;
};

std::ostream& operator<<(std::ostream &strm, const A &a) {
  return strm << "A(" << a.j << ")";
}

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