The time at which the CPP copy constructor occurs

If the first argument of a constructor is a reference to its own class type, and any additional arguments have default values, this constructor is a copy constructor

class numbered{ public :    numbered () {// constructor        0;    }    Numbered (const numbered& inputone) {// copy constructor        mysn =  INPUTONE.MYSN;         = Mysn +1;    } int mysn;};

The copy constructor has the following conditions:

#include <iostream>#include<string>#include<vector>using namespacestd;classnumbered{ Public: Numbered () {//constructor FunctionMYSN =0; } numbered (Constnumbered& Inputone) {//copy ConstructorMYSN =inputone.mysn; MYSN= Mysn +1; }intmysn;};voidf (numbered s) {cout<<s.mysn<<Endl;}intMain () {numbered A;//constructor FunctionNumbered b=a;//"1" copy constructorf (a);//"2" in the process of assigning a to the function f, a copy construction occurred//"3" returns an object from a function that returns a type other than a reference--like the 2nd//"4" Initializes an object in an array or a member of an aggregate class with a curly brace list (c++11)System ("Pause"); return 0;}

Operation Result:

As you can see from the Watch window: B.MYSN is 1 more than A.MYSN, which is caused by the copy constructor

As can be seen from the output, f (a) outputs 1, which is caused by the copy constructor.

There are four things about the copy constructor:

    Numbered b=a;//"1" copy constructor    F (a);//"2" in the process of assigning a to function f, a copy construction    //"3" returns an object from a function with a return type of non-reference-similar to the 2nd    //"4" with a curly brace list ( C++11) Initializes an object in an array or a member of an aggregation class

2nd, the 3rd most easy to ignore, should pay attention to.



The above is the basic content of the copy constructor, the following is a more complex example to analyze the difference between the copy constructor, constructor, etc.

#include <iostream>#include<cstdlib>using namespacestd;classa{ Public: A () {cout<<"Constructor called!"<<Endl; } A (inti): x (i) {cout<< I <<"Constructor called!"<<Endl; } A (ConstA &a) {x= a.x+1; cout<< x <<"copy Constructor called!"<<Endl; } A&operator=(ConstA &a) {x= a.x+Ten; cout<< x <<"copy Assignment function called!"<<Endl; return* This; }    ~a () {cout << x <<"destructor called"<<Endl;}Private:    //A (const a &a) {cout << "copy constuctor called!" << Endl;}    intx;}; A get_a () {A A (5); returnA;}intMain () {cout<<"-----1-----"<<Endl; A A=1;//1cout<<Endl; cout<<"-----2-----"<<Endl; A b= Get_a ();//2cout<<Endl; cout<<"-----3-----"<<Endl; b= A;//3cout<<Endl; cout<<"-----4-----"<<Endl; A C= A (2);//4cout<<Endl; cout<<"-----5-----"<<Endl; b=3;//5cout<<Endl; cout<<"-----6-----"<<Endl; A D= b;//6cout<<Endl; cout<<"-----7-----"<<Endl;     A e (b); //7cout<<Endl; return 0;}

Run results

For the 1th and 4th, why is there no copy constructor for this operation??

This place is not very clear?

Also please master advice. If I figure it out, I'll keep it up to date.

The time at which the CPP copy constructor occurs