Class constructor with default parameters

Question

I the next simple constructor:

Vector(double x=0, double y=0) : x(x), y(y) {}

void operator+=(const Vector& other) {
    this->x += other.x;
    this->y += other.y;
}

But when I call it like this

Vector b();
Vector a(1,1);

and try to do a += b; compiler gives me a lot of errors saying that no operators exist. However when I do like this: Vector b(0,0); or Vector b(0); everything works(((

Why would you think that such a constructor would enable usage of `+=`? If you want the operator, you have to overload it. That has nothing to do with constructors. But as a side note, you should make this constructor explicit, or simple numbers will implicitly convert to vectors as x coordinates. — Sebastian Redl, Sep 23 '14 at 13:54
@RobertMutke I do like to use `this` in such cases to be clear which of the two objects is being used. — Neil Kirk, Sep 23 '14 at 14:02
@NeilKirk kinda matter of taste, but still should be rather avoided http://stackoverflow.com/questions/2337540/when-should-you-use-the-this-keyword-in-c — Robert Mutke, Sep 23 '14 at 14:09
You know, you really, really want to mark that ctor `explicit`. — Deduplicator, Sep 23 '14 at 14:20

score 3 · Accepted Answer · answered Sep 23 '14 at 13:56

3

Vector b(); doesn't create an object. It declares a function.

Vector b;
Vector a(1,1);

should work.

answered Sep 23 '14 at 13:56

Luchian Grigore

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Class constructor with default parameters

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