Const's constant member function after the function; Form, characteristics and use of inline function

1 const Decorated constant member functions and const Class object

class Person{
//...
public:
	int age() const; //  Constant member function 
    int score(); //  Non member function 
private:
	int m_Age;
    int m_Score;
//...
}

• As mentioned above age() Function is a Constant member function , Constant member functions have the following characteristics
  • Express You cannot change the value of a member variable Function of
  • In constant member functions Only constant member functions can be called , Because very member functions , It is possible to change the value of member variables
• const Class objects can only call constant member functions in a class
  • Because since the class object is already const 了 , If you call a non member function , It is possible to change the content of the class , This is related to const Class object contradiction

bool cmp(const Person& a, Person& b) {
        return a.age() > b.age();  //  Compiler yes 
    	// return a.score() > b.score(); //  Compiler error , Because with const Class object called non member function 
}
//  among a yes const Class object , Only constant member functions can be called 

• For ordinary class objects , Then whether it is a constant member function or not , You can call

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2 Inline function

// The first inline function 
class Person{
//...
public:
	inline( Not to add ) int age() const { return m_Age; } //  Constant member function and inline function 
    int score(); //  Nonmember functions 
private:
	int m_Age;
    int m_Score;
//...
}

// The second kind of inline function 
inline void myFun()
{
    //....
    //....
}

• The above code shows Two expressions of inline functions
  • Write the member function implemented by the function directly in the definition of the class , Whether you add keywords or not inline Are all inline functions
  • Ordinary function definition , Add keywords before its functions inline, It becomes an inline function
• The function of inline function
  • In order to solve the efficiency problem of function call in the program
  • The essence is , In the compilation stage, the compiler replaces the call expression of the inline function in the program with the function body of the inline function , Used to avoid calling this function at run time , This saves the overhead of calling functions at runtime （ For example, context saving , Copy arguments, etc ）
• Points for attention of inline functions
  • Loop statements and switch statements cannot be used in inline functions
  • Generally, they are very short functions （ Such as 10 Within the line ）
  • The definition of an inline function must appear before the first call