Can anyone please tell me why the base class's constructor method is called twice?

#include <iostream>
using namespace std;

class A{
    public:
    A(){
        cout << "default constructor of base class" << endl;
    }
};

class B:public A{
    public:
    B(){
        A();
        cout << "default constructor of derived class" << endl;
    }
};

int main(int argc, char **argv){
    B b;
    return 0;
}

And I'm getting this unexpected result:

default constructor of base class
default constructor of base class
default constructor of derived class

Once constructing the base sub-object of the B object in main:

B b;

Once constructing the temporary A object in the constructor of B:

A();

Perhaps you meant to initialise the A sub-object; do that in the initialiser list, not the constructor body:

B() : A() {
    cout << "default constructor of derived class" << endl;
}

although, in this case, that would do exactly the same thing as leaving it out altogether.

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