C++ default constructors absence and I cannot compile

Question

I have this very simple class

class myclass {

public:
    int id;
    double x, y, z;

    myclass() = default; // If I omit this line I get an error
    myclass(int ID, double X, double Y, double Z): id(ID), x(X), y(Y), z(Z) {};
};

If I omit the line with the line myclass() = default; and then attempt at creating one object

#include <vector>
using namespace std;
int main() {

    int ID = 0;
    double X = 1.0, Y = 2.0, Z = 3.0;
    vector<myclass> a_vector(10);

    myclass an_object(ID,X,Y,Z);

    return 0;
}

I get an error no matching function for call to ‘myclass::myclass().

Why does this happen? When is it mandatory to specify the constructor taking no parameter as default?

This is probably a very easy question, but other questions on constructors seemed aimed at very specific issues with constructors, so I thought it might be worthwhile.

Answer 1

Once you provide any constructor(s), the compiler stops providing other ones for you - you become in full control. Thus when you have one that takes some parameters, the one that takes no parameters is not provided anymore.