A class declaration problem.

Question

4.00/5 (1 vote)

See more:

I am currently programming a simple C++ application. I downloaded some source code from a website, but i don't understand the a class declaration.

Here's the code ;

C++

class myClass
{
public:

	myClass(int sub) : main(sub) {} //what's up with this line ?
	int	main;

	int DoCalc();
};

Please, Need help !

Posted 8-Aug-12 21:48pm

Captain Price

Add a Solution

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

pasztorpisti · Accepted Answer · 2012-08-08T22:38:00

Solution 2

That stuff is called the "initialization list". Read this article about it:
http://www.cprogramming.com/tutorial/initialization-lists-c++.html[^]

You could just say

C++

main = sub;

in the constructor body instead of the initializer list in case of a simple int member but sometimes only initializer lists can do the job. For example when you have a base class or a member variable whose type is a class that doesn't have a default constructor. Same is true for a reference that is the member of your class. Read the linked article that has example code for these.

Posted 8-Aug-12 22:38pm

pasztorpisti

Updated 9-Aug-12 20:39pm

v2

Comments

Captain Price 9-Aug-12 12:56pm

thanks, i got it. But the syntax is really confusing.

Albert Holguin 9-Aug-12 23:45pm

I remember the first time I saw this syntax I thought the same thing... :)

pasztorpisti 10-Aug-12 2:37am

Yes, its confusing and ugly. But not in all languages, for an example in java you have to initialize such members in the constructor body just like you do it with every other regular member but you have to write these mandatory initializations to the beginning of your constructor body.

PS: Forgot to mention that you have to use initializer list for example to initialize a reference too if it is a member of the class.

Volynsky Alex 10-Aug-12 3:10am

Good answer!+5!
A declaration introduces one or more names into a program. Declarations can occur more than once in a program. Therefore, classes, structures, enumerated types, and other user-defined types can be declared for each compilation unit. The constraint on this multiple declaration is that all declarations must be identical. Declarations also serve as definitions, except when the declaration:

// Declare class CheckBox.
class CheckBox : public Control
{
public:
Boolean IsChecked();
virtual int ChangeState() = 0;
};

For more information about classes and class members, see here:
http://msdn.microsoft.com/en-us/library/0kw7hsf3.aspx
http://msdn.microsoft.com/en-us/library/4a1hcx0y.aspx
http://www.cplusplus.com/doc/tutorial/classes/

Argonia · Accepted Answer · 2012-08-08T22:16:00

Solution 1

It basically means that the variable main will get the value sub when the new member of myClass is created with that constructor
Note : you must be careful with these things . It resembles calling the constructor of base class

Posted 8-Aug-12 22:16pm

Argonia

Comments

Captain Price 9-Aug-12 12:56pm

ok