CODEWITHSUNDEEP
c++constructor
Cleverboy
Cleverboy

Reputation: 13

Class object is initialised without defining member variables

I am learning C++ and came across this code where the constructor is initialised without declaring member variables. Also, the object is created without any parameters. Wouldn't a default constructor be called instead?

Also, if this class is inherited, will the derived class have access to x and y?

// Example program

#include <iostream>
#include <string>

class game
{
public:
    game(int x = 0, int y = 100); // Do they get defined as members?
    int z; 
};

game::game(int x, int y) : z(x)
{
    std::cout << x;   
}

int main()
{
    game g; // passed w/o parameters.
    return 0; 
}

Upvotes: 1

Views: 55

Answers (1)

Arnav Borborah
Arnav Borborah

Reputation: 11807

Also the object is created without any parameters. Wouldn't a default constructor be called instead?

You declare your constructor as follows:

game(int x = 0, int y = 100);

And the implementation:

game::game(int x, int y) : z(x)
{
    std::cout << x;   
}

Since you have specified default arguments for the constructor, when you call:

game g;

It is the same as calling:

game g {0, 100};

Since the default arguments are provided for the constructor.

game(int x = 0, int y = 100); // Do they get defined as members.

They don't get defined as members, unless you set their values to members in the class. x and y both go out of scope at the end of the constructor.

Also, if this class is inherited will the derived class have access to x and y?

Not directly, which you can see as follows:

class Derived : public game
{
public:
    Derived();
};

Derived::Derived() : game(100, 100) //Or whatever arguments
{
    //...
}

Upvotes: 2

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