constructors in c++ with examples

Constructors:

Special function

Without return type

Name of class and constructor are same

Default constructors:

This constructor automatically created when we create an object

No need to call

This constructor has no argument pass

#include<iostream>

using namespace std;

class employee

{

    string name;

    int employee_id;

    int selary;

    public:

    employee()

    {

        cout<<"enter name"<<endl;

        cin>>name;

        cout<<"enter employee id"<<endl;

        cin>>employee_id;

        cout<<"enter selary"<<endl;

        cin>>selary;

    }

    void display()

    {

        cout<<"-----------------------"<<endl;

        cout<<"name             "<<name<<endl;

        cout<<"employee  "<<employee_id<<endl;

        cout<<"selary         "<<selary<<endl;

        cout<<"-----------------------"<<endl;

    }

};

int main()

{

    employee s2;

    s2.display();

    return 0;

}

Parameterized constructor:

This type of constructor has argument pass in the constructor

We call it and add parameters

#include<iostream>

using namespace std;

class employee

{

    string s_name;

    int roll_no;

    int s_marks;

    public:

    employee(string name,int roll ,int marks)

    {

        s_name=name;

        roll_no=roll;

        s_marks=marks;

    }

    void display()

    {

        cout<<"------------------------------"<<endl;

        cout<<"name       "<<s_name<<endl;

        cout<<"roll no    "<<roll_no<<endl;

        cout<<"marks      "<<s_marks<<endl;

        cout<<"------------------------------"<<endl;

    }

};

int main()

{

    employee s("waqas",17,487);

    s.display();

;

    return 0;

}

Copy constructors:

it used to copy of one object to another

initialization of an object with another object called copy constructor

We also need to call it for use

Syntax:

Class name (const class name & object name)

#include<iostream>

using namespace std;

class student

{

    string s_name;

    int roll_no;

    int s_marks;

    public:

    student (string name, int roll, int marks)

    {

        s_name=name;

        roll_no=roll;

        s_marks=marks;

    }

    student(student &s)

    {

        s_name=s.s_name;

        roll_no=s.roll_no;

        s_marks=s.s_marks;

    }

    void display()

    {

        cout<<"-----------------------------------"<<endl;

        cout<<"name                         "<<s_name<<endl;

        cout<<"roll no                      "<<roll_no<<endl;

        cout<<"marks                        "<<s_marks<<endl;

        cout<<"-----------------------------------"<<endl;

    }

};

int main()

{

    student s1("waqas",17,487);

    student s3(s1);

    cout<<"parameterized constuctor"<<endl;

    s1.display();

    cout<<"copy constutor"<<endl;

    s3.display();

    return 0;

}