了解操作员重载的问题

Question

I am reading TCPPPL by Bjarne Stroustrup and I came across the following piece of code (shown below). I have two questions:

1. Where is the body of the function operator+? I mean there is only the declaration of the function in class X.

2. What does the line X(int) mean? Is this the constructor with int as a parameter or something else?

---

 class X {
     public:
     void operator+(int);
     X(int);   
 };

 void operator+(X,X);
 void operator+(X,double);

 void f(X a)
 {
     a+1;    // a.operator+(1)
     1+a;    // ::operator+(X(1),a)
     a+1.0;  // ::operator+(a,1.0)
 }

Answer 1

What does the line X(int) mean?

X(int) is a declaration of a constructor accepting a single integer parameter. Definition is missing.

Where is the body of the function operator+

Wherever you defined it.

This code won't work without the correct definitions.

Answer 2

1) Where is the body of the function operator+? I mean there is only the declaration of the function in class X.

The definition (body) of operator+ can be anywhere. The code is obviously not a complete program (there is no main ). Therefore, the definitions might be below the shown code or even in another compilation unit.

2) What does the line X(int) mean? Is this the constructor with int as a parameter or something else?

This is a declaration of a converting constructor of class X that accepts an integer as an argument.