What is this syntax?

Question

Possible Duplicate:
What does a colon following a C++ constructor name do?

I am finding this syntax strange in C++

TagDetails::TagDetails(QWidget *parent) :
QDialog(parent),
ui(new Ui::TagDetails)

This is declaration of constructor in C++... What does the thing after colon stand for, i.e. what does ui(new Ui::TagDetails) mean here? What is the colon for?

vitaut · Accepted Answer · 2010-11-09T16:34:45.440

5

It is a member initialization list.

ui(new Ui::TagDetails) means that the member variable ui is initialized with the pointer to newly allocated object of type Ui::TagDetails.

edited Nov 09 '10 at 16:34

answered Nov 09 '10 at 16:26

vitaut

49,672
25
199
336

And note that you should use the member initialization list to initialize all attributes and base classes. – Šimon Tóth Nov 09 '10 at 16:38
@Let_Me_Be: Yes, sir! =) – vitaut Nov 09 '10 at 16:44
Just one question. In which reference book did you find this ? – chai Nov 10 '10 at 05:12
@chai: Probably in this one: http://www.amazon.co.uk/C-Programming-Language-Special/dp/0201700735 – vitaut Nov 10 '10 at 06:15

score 1 · Answer 2 · answered Nov 09 '10 at 16:26

1

What you're looking at is an initializer list. The ui member of the class is being initialized with a value of new Ui::TagDetails, where TagDetails is defined inside the class or namespace Ui.

answered Nov 09 '10 at 16:26

Mark Ransom

299,747
42
398
622

score 0 · Answer 3 · answered Nov 09 '10 at 16:27

0

This is called an initialization list. See C++ FAQ for the pros of initialization lists over assignment.

I'm not familiar with the site, but this page seems to explain quite thoroughly how things work.

answered Nov 09 '10 at 16:27

icecrime

74,451
13
99
111

What is this syntax?

3 Answers3