The C++ standard's rule for selecting a constructor

Visual C++ 2003 EE is used.

The program that follows

#include "stdafx.h"

#include <iostream>
#pragma hdrstop
#include <conio.h>

class A {};
class B
{
public:
    B() { std::cout << "Inside B()" << std::endl; b = 0; }
    B( const A & ) { std::cout << "Inside B( const A & )" << std::endl; b =
1; }
    B( const B & ) { std::cout << "Inside B( const B & )" << std::endl; b =
2; }
    int get_b() const { return b; }
private:
    int b;
};

int _tmain(int argc, _TCHAR* argv[])
{
    A a;
    B b1( a );
    std::cout << "b1.b = " << b1.get_b() << std::endl;
    B b2 = a;
    std::cout << "b2.b = " << b2.get_b() << std::endl;
    B b3 = B( a );
    std::cout << "b3.b = " << b3.get_b() << std::endl;

    return EXIT_SUCCESS;
}

gives the result

Inside B( const A & )
b1.b = 1
Inside B( const A & )
b2.b = 1
Inside B( const A & )
b3.b = 1
Press any key to continue . . .

Is it a bug that b3.b = 1? I guessed that b3.b must be equal to 2.

If the copy constructor will be declared as private then the error

error C2248: 'B::B' : cannot access private member declared in class 'B'

will be issued for the statement

B b3 = B( a );

O'k. However what constructor must be called for the statement B b2 = a; ?

If the keyword explicit will be placed before B( const A & ) the error

error C2440: 'initializing' : cannot convert from 'A' to 'B'

will be issued for the statement

B b2 = a;

Vladimir Grigoriev