C + + Constructor _ copy constructor

Copy constructor

Functions automatically generated by the system:

Common constructors

Copy constructor

If you define a normal constructor, the system will no longer automatically generate ordinary constructors;

If you define a copy constructor, the copy constructor is no longer automatically generated by the system.

If there is no custom copy constructor, the system automatically generates a default copy constructor.

The copy constructor is automatically called when the instance object is initialized with direct initialization or copied.

A copy constructor is a special constructor that initializes a newly created object when it is created by using an object that was previously created in the same class. Copy constructors are typically used to:

• Initializes a newly created object by using another object of the same type.

• The Copy object passes it as a parameter to the function.

• Copies the object and returns the object from the function.

If a copy constructor is not defined in the class, the compiler defines it by itself. If a class has a pointer variable and has a dynamic memory allocation, it must have a copy constructor. The most common form of a copy constructor is as follows:

ClassName (const classname &obj) {   //  Body of Constructor }

Defining formats

　　　　Class name (const class name & variable name)

class student{public:    "Jim"//  General Constructor    Student (const//  copy constructor private:    string  m_strname;}

code example:

Demo.cpp

#include <iostream>#include<stdlib.h>#include<string>#include"Teacher.h"using namespacestd;/*************************************************************************teacher Class Custom copy constructor data member: Name Age member function: Wrapper function for data members *************************************************************************/voidTest (Teacher t) {}intMainvoid) {Teacher T1; //Calling normal functionsTest (T1);//Call copy ConstructorTeacher t2 = t1;//Call copy ConstructorTeacher t3 (t1);//Call copy ConstructorSystem ("Pause"); return 0;}

Teacher.h

#include <string>using namespacestd;classteacher{ Public:    //declaring constructors, parameters given default valuesTeacher (stringName ="CJJ",intAge = A); //declaring copy ConstructorsTeacher (ConstTeacher &tea); //declare member functions and list all the member functions    voidSetName (string_name); stringGetName (); voidSetage (int_age); intgetage ();Private:    stringM_strname; intM_iage; };

Teacher.cpp

#include"Teacher.h"#include<iostream>using namespacestd;//define constructors, use initialization lists, initialize parameters of constructors//M_imax (m) is a constant and can only be initialized with an initialization listTeacher::teacher (stringNameintAge ): M_strname (name), M_iage (age) {cout<<"Teacher (String name,int age)"<<Endl;}//Defining copy ConstructorsTeacher::teacher (ConstTeacher &tea) {cout<<"teacher::teacher (const Teacher &tea)"<<Endl;}//out-of-class definitions, function bodies that write out member functionsvoidTeacher::setname (string_name) {M_strname=_name;}stringTeacher::getname () {returnM_strname;}voidTeacher::setage (int_age) {M_iage=_age;}intTeacher::getage () {returnm_iage;}

Operation Result:

C + + Constructor _ copy constructor