What does a : do after a function declaration?

Question

Rectangle(Point2D center, double w, double h, double r, double g, double b):center(center)
    {
        ...
    }

What does the :center(center) part of this code do?

It sets a variable owned by the class to the value encapsulated inside the parenthesis. — , Mar 02 '14 at 07:55
[Related question](https://stackoverflow.com/questions/4589237/c-initialization-lists) — ajp15243, Mar 02 '14 at 07:56
Note that this syntax is only allowed in constructors, not function declarations in general. — TonyK, Mar 02 '14 at 07:57

Avt · Answer 1 · 2014-03-02T09:26:24.727

1

: initializes center member with center parameter.

In most case (not always!) your code

Rectangle(Point2D center, double w, double h, double r, double g, double b):center(center)
{
    ....
}

could be replaced with

Rectangle(Point2D center, double w, double h, double r, double g, double b)
{
    this->center = center;
    ....
}

You can read more about initialization lists in C++ here

edited Mar 02 '14 at 09:26

answered Mar 02 '14 at 07:55

Avt

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Why not just have center as a function parameter? – Programmer Mar 02 '14 at 08:13
You should explain the difference between the two. – juanchopanza Mar 02 '14 at 09:19
I have added a link about initialization lists to make my answer complete. – Avt Mar 02 '14 at 09:40

score 0 · Answer 2 · answered Mar 02 '14 at 08:07

It's used to initialize the element . Since C++ is object oriented everything is treated as object even datatypes. so when you use initialization list the object are initialized when the object is created for it.

This is considered to better(faster) way then assigning to the variable directly.

As definition and declaration happens in one go.

What does a : do after a function declaration?

2 Answers2