Explanation of the following syntax?

[Moonraker101]

I recently stumbled onto this syntax while reading a piece of code. Its just a struct declaration

struct Vector2D
{
  double x;
  double y;

Vector2D():x(0.0), y(0.0){}
Vector2D(double a, double b):x(a), y(b){}

}

I am referring to the Vector2D(): type syntax specifically. I have seen the the use of colons for bit field, but not in this manner. Can somebody explain whats happening?

[norm b]

Here you go: http://www.learncpp.com/cpp-tutorial/101-constructor-initialization-lists/

[Moonraker101]

Lol thanks @norm b,

I could of done that myself, but I didn't know the proper terminology because I hadn't seen it used before in structs. Again thanks