＆c ++中的含义是什么？

Question

I want to know the meaning of & in the example below:

class1 &class1::instance(){

///something to do

}

Answer 1

The & operator has three meanings in C++.

• "Bitwise AND", eg 2 & 1 == 3
• "Address-of", eg: int x = 3; int* ptr = &x; int x = 3; int* ptr = &x;
• Reference type modifier, eg int x = 3; int& ref = x; int x = 3; int& ref = x;

Here you have a reference type modifier. Your function class1 &class1::instance() is a member function of type class1 called instance , that returns a reference -to- class1 . You can see this more clearly if you write class1& class1::instance() (which is equivalent to your compiler).

Answer 2

This means your method returns a reference to a method1 object. A reference is just like a pointer in that it refers to the object rather than being a copy of it, but the difference with a pointer is that references:

• can never be undefined / NULL
• you can't do pointer arithmetic with them

So they are a sort of light, safer version of pointers.

Answer 3

它是一个对象的引用（不使用指针算术来实现它）。

Answer 4

它返回对定义它的类型的对象的引用。

Answer 5

In the context of the statement it looks like it would be returning a reference to the class in which is was defined. I suspect in the "Do Stuff" section is a

return *this;

Answer 6

It means that the variable it is not the variable itself, but a reference to it. Therefore in case of its value change, you will see it straight away if you use a print statement to see it. Have a look on references and pointers to get a more detailed answer, but basecally it means a reference to the variable or object...