Why I have to use initialization list to use constructor delegation in c++?

I know we have to use an initialization list to use constructor delegation in c++. But why we can’t use it in another way? For example in the code below, constructor delegation is not working. It is not setting the health=pHealth.But the court << "I am the main constructor" is printing on the console.It means the constructor has been called but not set the value to the health parameters.

code-

#include <iostream>


using namespace std;

class Player{
    int health;
    public:
    Player(int pHealth){
        health=pHealth;
        cout << "I am main constructor";
    }
    Player(){
        Player(40);
    }

    void check(){
        cout << health;
    }

};

int main(int argc, char const *argv[])
{
    Player x;
    x.check();
    return 0;
}

>Solution :

Your program is creating two objects.

1. using x
2. using "Player(40);" inside constructor
   Sample:

#include <iostream>
using namespace std;
class Player
{
                int health;
        public:
                Player(int pHealth)
                {
                        cout << "One argument constructor this: " << this << "\n";
                        health=pHealth;
                }
                virtual ~Player()
                {
                        cout << "destructor this: " << this << "\n";
                }
                Player()
                {
                        cout << "Default constructor this: " << this << "\n";
                        Player(40);     // Create new object using one argument constructor.
                }
                void check()
                {
                        cout << "health: " << health << " this: " << this << "\n";
                }
};
int main(int argc, char const *argv[])
{
        Player x;
        x.check();
        return 0;
}

Output:

$ g++  -g -Wall 73596563.cpp -o ./a.out
$  ./a.out
Default constructor this: 0xffffcc10
One argument constructor this: 0xffffcbd0
destructor this: 0xffffcbd0
health: -13184 this: 0xffffcc10
destructor this: 0xffffcc10

Hence 0xffffcbd0 being created inside that default constructor.
Hence updated your code same using:

                Player():health(40)
                {
                        cout << "Default constructor this: " << this << "\n";
                        // Player(40);  // Create new object using one argument constructor.
                }

Output obtained after above update:

$ ./a.out
Default constructor this: 0xffffcc10
health: 40 this: 0xffffcc10
destructor this: 0xffffcc10

Few more comment:

Player x;
x.check();
// Call constructor without creating object.
Player();
Player(2003);

Hence related output:

$ ./a.out
Default constructor this: 0xffffcbf0
health: 40 this: 0xffffcbf0
Default constructor this: 0xffffcc00
destructor this: 0xffffcc00
One argument constructor this: 0xffffcc10
destructor this: 0xffffcc10
destructor this: 0xffffcbf0