Why can't I instantiate an object in a class?

Question

I have these three codes:

#pragma once

class Rect
{
private:
    int m_Thing;
public:
    Rect(int thing)
    {
        m_Thing = thing;
    }

    void create(int thing)
    {
        m_Thing = thing;
    }
};

#pragma once
#include "Rect.h"

class Brick
{
private:
    Rect floatRect;
public:
    Brick()
    {
        floatRect.create(28);
    }
};

#include "mre.h"
#include <iostream>

int main()
{
    Brick brick;
}

For some reason, I get an error that says I need a default constructor. I make one, and then I get an unresolved external symbol error on the Rect object. That's where I'm stuck. How can I instantiate it?

Answer 1

When you call an default constructor of a class, all of its members are default constructed unless specified some other way. If we wanted to write what happens explicitly in the call of Brick(), it would look like this.

Brick() : floatRect()
{
    floatRect.create(28);
}

Here we can see that in the member initializer list it attempts to call the default constructor of Rect, which is implicitly deleted because you have a user-defined constructor. If you want to create Rect, you can do the following.

Brick() : floatRect(28)
{
    
}

The member initialized field is purposely for initializing or passing arguments to the constructors of members.