Question

I’m a PHP developer trying to write some C++.

I’m having trouble with assigning an object as an another object’s property. In PHP, I’d write this:

class A {
    public $b;
}
class B {

}

$a = new A;
$a->b = new B;

How do I do that in C++? I got this so far:

class A {
    B b;
public:
    void setB(&B);
};
class B {

};

void A::setB(B &b)
{
    this->b = b;
};

A * a = new A();
B * b = new B();
a->setB(b);

What am I doing wrong?

Answer 1

A couple changes will make it compile:
1. class B needs to be declared before A so that it can be used in class A
2. The declaration setB(&B) needs a minor change to setB(B&)

class B {
};

class A {
    B b;
public:
    void setB(B&);
};
void A::setB(B &b)
{
    this->b = b;
};

int main ()
{   
A * a = new A();
B * b = new B();
a->setB(*b);
}   

To make it more efficient consider the adding the following constructor that accepts B as an argument and the initializes the member variable ‘b’. This will use a copy constructor on the ‘b’ member variable instead of using the default constructor and then the assignment operator.

A(B& b_) : b(b_) 
{
}