Extremely important analysis

# Include <iostream> using namespace STD; Class A {public: A () {value ++; cout <"default a" <Endl;} A (const &) {value ++; cout <"const a" <Endl ;}a operator = (const A & A1) {cout <"operator =" <Endl; return A (A1);} void F () {cout <"value is" <value <Endl ;}~ A () {cout <"~ A "<Endl;} PRIVATE: static int value;}; int A: value = 0; void F1 (A A1) {a1.f (); cout <"f1" <Endl;} a F2 () {cout <"F2" <Endl; return a ();} void F3 () {A A1, a2; F1 (A1); a2 = F2 ();} int main () {F3 (); Return 0 ;}

The result is

Default A1 in a F3 calls Constructor
Default A2 in a F3 calls the constructor
The a variable in const a F1 calls the constructor with A1 as the parameter.
Value is 3 at this time there are three A objects, so the value is 3
F1 Print Output F1
~ The local variable in a F1 is out of the scope. At this time, the Destructor is called.
F2 F2 print out F2
Default a F2 calls the default constructor
Operator = F2 in F3, the output is printed only when the = Operator is called.
Const
~ A
~ A
~ A
~ A

This is actually a problem. Generally, * This (=, + =,-=, etc.) must be returned if a value is assigned)

Similar to the following

#include <iostream>using namespace std;class a{    public:        a(){            value ++;            cout <<"default a"<<endl;        }        a(const a&){            value ++;            cout <<"const a"<<endl;        }        a& operator=(const a& a1){            cout <<"operator ="<<endl;            return *this;        }        void f(){            cout <<"value is "<<value <<endl;        }        ~a(){            cout <<"~a"<<endl;        }    private:        static    int value;};int a::value = 0;void f1(a a1){    a1.f();    cout <<"f1"<<endl;}a f2(){    cout <<"f2"<<endl;    return a();}void f3(){    a a1,a2;    f1(a1);    a2 = f2();}int main(){    f3();    return 0;}

  4 class a{  5     public:  6         a(int i):value(i){}  7         ~a(){cout <<"~a"<<endl;}  8         a& operator=(const a& a1){  9             this->value = a1.value; 10             return *this; 11         } 12         int get(){return value;} 13     private: 14         int value; 15 };

The best method is =, + =,-=, and so on. These symbols cannot cause constructors,

Remember this time

A a1 = 10;

At this time, the constructor is called. Although the symbol = is used, this must be high-definition.

Result:

Default
Default
Const
Value is 3
F1
~ A
F2
Default

Operator =
~ A
~ A
~ A

 

Extremely important analysis