What is Constructor in C++ with examples?

In this chapter of C++ interview questions, we will learn about:

• what is constructor in c++?
• syntax of constructor in c++
• example of constructor in c++

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What is Constructor in C++?

• Constructor is a 'special' member function, which is used for initialization of all objects. 
• Why constructor is 'special'? - because the class name and constructor name is same.
• Compiler calls it when an object is created.
• It initialize values after storage allocation of object.

Syntax of constructor in C++

Given below is example depicting syntax of constructor in c++:

class Rectangle
{
double length,breadth;

public:
Rectangle(void); // constructor called
};

Rectangle :: Rectangle(void) // constructor defined
{
length=0;
breadth=0;
}

Example of constructor in c++

Given below is an example of constructor in c++:

#include <iostream> 
using namespace std; 

class Rectangle 
{ 
public: 
double sarea(double length, double breadth); 
double garea(void); Rectangle(void); // Constructor Created 
private: double a; 
}; 
Rectangle::Rectangle(void) // definition of Constructor 
{ 
   cout<<"Object is here"; cout<<endl; 
} 

// defining other functions 
double Rectangle::sarea(double length, double breadth) 
{ a=length*breadth; } 
double Rectangle::garea(void)
{ 
   return a; 
}

int main() 
{ 
 Rectangle R;
 R.sarea(10.0,12.0); 
 cout<<"Area of Rectangle"<<" "<<R.garea();
 cout<<endl; 

return 0; 
}

Output

Object is here

 Area of Rectangle 120.0