Basic class advice needed

[Gerald Bates]

The CPP language has changed and I am now studying an online book, but I have some basic questions on this simple class.

#include <iostream>


using namespace std;


class vmSize {
public:
    vmSize() = default;
    vmSize(int nWidth, int nHeight) { m_nWidth = nWidth, m_nHeight = nHeight; }


    int GetWidth() const { return m_nWidth; }
    int GetHeight() const { return m_nHeight; }


private:
    int m_nWidth {}, m_nHeight {};
};


int main()
{
    vmSize mySize;
    cout << "width " << mySize.GetWidth() << "\n";
    cout << "height " << mySize.GetHeight() << "\n";


    vmSize anotherSize{ 10, 5 };
    cout << "\nwidth " << anotherSize.GetWidth() << "\n";
    cout << "height " << anotherSize.GetHeight() << "\n";


    return 0;
}

1. With the default constructor, my program shows both width and height initialized to 0, am I right in thinking that these two variables will always be 0 irrespective of what compiler I use? I did not place a 0 within the curly braces of the private data members of the class?

2. I could make the default c'tor redundant by doing this:

  vmSize(int nWidth = 0, int nHeight = 0) { m_nWidth = nWidth, m_nHeight = nHeight; }

Is this good programming practice to do this, or is it better to have a default c'tor and not make this change?

3. Looking at this simple code I can't help but ask, What if I wanted two other c'tor's that take two doubles and another that takes two floats for width and height. Would I need to write these two other c'tor's, or is there a way of writting ONE c'tor that could take int, double or float and not complain. Hope this does not sound silly! Thinking of code reduction?

Thank you.

[2kaud]

1. Yes. {} is the default initializer. The default value is specified for a type. For a int/double et al it is 0.

2. You constructor should be :

vmSize(int nWidth, int nHeight) : m_nWidth(nWidth), m_nHeight(nHeight) {}

I prefer a separate default constructor.

vmSize() {}

where the member variables are value initialized.

3). You'd use a templated class:

#include <iostream>

using namespace std;

template <typename T>
class vmSize {
public:
	vmSize() {};
	vmSize(T nWidth, T nHeight) : m_nWidth(nWidth), m_nHeight(nHeight) {}

	T GetWidth() const { return m_nWidth; }
	T GetHeight() const { return m_nHeight; }

private:
	T m_nWidth {}, m_nHeight {};
};

int main()
{
	vmSize<int> mySize;

	cout << "width " << mySize.GetWidth() << "\n";
	cout << "height " << mySize.GetHeight() << "\n";

	vmSize<int> intSize {10, 5};

	cout << "\nwidth " << intSize.GetWidth() << "\n";
	cout << "height " << intSize.GetHeight() << "\n";

	vmSize<double> doubleSize {11.34, 13.56};

	cout << "\nwidth " << doubleSize.GetWidth() << "\n";
	cout << "height " << doubleSize.GetHeight() << "\n";
}

[Gerald Bates]

Many thanks 2kaud, this has really helped.