Question

Is it possible to initializate a class like this?

Quaternion::Quaternion(){ //default without arguments
    Quaternion(0.,V3(0.,0.,0.));
}


Quaternion::Quaternion(double s, V3 v){ //with scalar and vector as a argument
    coords[0] = s;
    coords[1] = v[0];
    coords[2] = v[1];
    coords[3] = v[2];
}

because this is the output:

QUATERNION TEST
(2.122e-313:-3.22469e-232:2.122e-313:-1.998) //instanciated with Quaternion q;
(4:1:2:3) // instanciated with the Quaternion q(4,1,2,3);
(4:-1:-2:-3) // conjugated of the one above

and first one is not initializated as 0. as it should be… why?

Answer 1

Not in C++03, but the recent version of C++ allows delegating constructors:

Quaternion() : Quaternion(0.0, V3(0.0,0.0,0.0)) { }

In a delegating constructor, the initializer list must have precisely one element, which is another constructor (and obviously there mustn’t be any circular references).

Pre-C++11 you don’t really get around copy/pasting if you want to actually initialize your class members directly in the constructor. Maybe you would like to use default arguments, though? Some people object to those….

explicit Quaternion(double s = 0.0, V3 v = V3(0.0,0.0,0.0)) { /* ... */ }