[C++] Initialize member variable with constructor initialization list

Member initializer list is useful in case of initializing member variables of const or reference type, and for class has no member initialization inside its default constructor. 


Example:

#include <iostream>
using namespace std;

class Point {

    private:
      int _x;
      int _y;
      
    public:
      Point(int x, int y): _x(x), _y(y) {};
      
      void print();
      
};

void Point::print()
{
cout<<"x: "<<_x<<" y: "<<_y<<endl;
}

int main() {

Point *p = new Point(3,4);
p->print();
 
return 0;
}


We can write our constructor in two ways as below.

The difference between them is that in Method B,  the 'initialization' for _x and _y happened after object is created and their values are actually changed by assignment operation.  While in Method A _x and _y is initialized before constructor runs.

Method A:
    public:
      Point(int x, int y): _x(x), _y(y) {};

Method B:
    public:
      Point(int x, int y): 
     {
            _x = x;
            _y = y;
     }