在运算符重载中返回引用的重要性是什么？

Question

任何人都可以解释为什么在重载运算符时需要返回引用，例如

friend std::ostream& operator<< (std::ostream& out, const std::string& str)

Answer 1

It is to make "chaining" of the operator work, in examples like this:

std::cout << "hello," << " world";

If the first (leftmost) use of the operator<<() hadn't returned a reference, there would not be an object to call for the second use of the operator.

Answer 2

这是为了操作符链接（如果你返回一个指针，你必须取消引用它），并且不要制作一个可能庞大且昂贵的对象副本（如果你返回一个值），如果它甚至可以这样做的话。

Answer 3

A general rule, stated by Scott Meyers in Effective C++, is that when in doubt, "do as the ints do". So for example, operator= should return a reference so code like this works:

MyClass A, B, C;
A = B = C = 0;