Implicit type conversion of C ++

Implicit type conversion of C ++

C ++ is a complex language with many "fun" features. Learning C ++ is like picking up a rock on the beach, maybe you can build your own little castle with a small rock.

After talking nonsense, let's talk about the stone we found: implicit type conversion.

Source: Translation of Objective C ++ lostmouse

 

Class TestInt
{

Public:
Int GetData () const {return I ;};
TestInt (int ii): I (ii) {}; // Constructor

Private:
Int I;

};

Void fun (TestInt t)

{
Cout <t. GetData () <endl;
}

Int main ()

{

Fun (10 );

Return 0;

}

Running result:

10

Why does the fun function need parameters of the TestInt type? Can it be passed into the int type,

Before looking for the cause, comment out the constructor and re-compile the constructor. The result is that the following error occurs: conversion from 'int' to non-scalar type 'testint.

It seems a little eye-catching. The successful call estimation is related to the constructor of the class. In fact, this is the implicit type conversion in C ++:

The compiler knows that the value of fun is int and the function requires TestInt. However, the compiler also knows to call the TestInt constructor to convert int into a suitable TestInt,

We know that the function will generate a temporary variable when passing the value. The current situation is similar to const TestInt t (10), so the result is shown above.

 

Example in Objective C ++:

Class Month {
Public:
Static const Month Jan () {return 1 ;}
Static const Month Feb () {return 2 ;}
...
Static const Month Dec () {return 12 ;}

Int asInt () const // For convenience, make the Month
{Return monthNumber;} // can be converted to int

Private:
Month (int number): monthNumber (number ){}

Const int monthNumber;
};

At the beginning, I didn't understand how to call this class, and on static const Month Jan () {return 1 ;}

The return value of this function has a lot of questions. Why is the return type Month, but the function can return an int.

I couldn't figure it out, so I had to break into the compiler and try again and again, and finally figured out the usage of this class,

In fact, this class is to get the Month of a const: Month jan = Month: Jan (); in this way, we will get the object representing January.

Static const Month Jan () {return 1;} successfully utilizes implicit type conversion, but the current constructor is

Private to prevent users from creating new month.

 

"Reading a swimming book doesn't really make you learn to swim." The same is true for programming.