switch structure + cpp

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C++

Hello,
I want the codes to draw circle, dot, line and ellipse in c++ with switch structure, please.

Posted 13-Dec-11 8:41am

kingsoroush

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OriginalGriff 13-Dec-11 14:51pm

Have you tried anything at all yourself?

Sergey Alexandrovich Kryukov 13-Dec-11 14:58pm

It's good that OP did not try it -- please see my answer.
--SA

Sergey Alexandrovich Kryukov 13-Dec-11 14:56pm

Why?
--SA

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Sergey Alexandrovich Kryukov · Accepted Answer · 2011-12-13T08:56:00

Solution 1

Doing it with switch is a huge abuse of C++ as an object-oriented language.

You should create an abstract base class like Shape and derive the classes Line, Ellipse, Rectangle and more. Better don't include Point in the hierarchy as it cannot have the same rendering. Instead, create a structure Location and make an instance of it a member of Shape. Don't include Circle and Square as they would work much better as special cases of Ellipse and Rectangle, just add special constructors and/or factory methods.

…I feel I'm wasting my time. What you really need is to read some elementary manuals on C++ and OOP.

—SA

Posted 13-Dec-11 8:56am

Sergey Alexandrovich Kryukov

Updated 13-Dec-11 8:58am

v2

Comments

[no name] 13-Dec-11 14:58pm

You do not wasting your time! You are helping us keep things clear!
And also the different elementary manuals do not correspond on such aspects :)
Regards

Sergey Alexandrovich Kryukov 13-Dec-11 15:32pm

Thank you for your good words!
--SA

[no name] 13-Dec-11 15:38pm

Lot of times I have problems (self made…) with your (sometimes hard) comments. But with a little bit distance, most time I have to say to me; this –SA is really an expert.
So please keep on sharing your knowledge...and maybe become a liitle bit more soft with beginners (also like me) Thx.
Regards

Sergey Alexandrovich Kryukov 13-Dec-11 16:02pm

Thank you again. I really appreciate your advice. I'm from much more demanding type of culture and I have a lot of positive experience of its efficiency, that's why. You should understand that on a personal level I'm very benevolent. It needs some social experience to understand the difference.
--SA

[no name] 13-Dec-11 16:16pm

Many thanks to you for your engagement/employment here...(sorry english is not my native lng, hope you will understand it what I try to say). I think I will learn how to become compatible. So let's go and let us learn.
Regards

Addy Tas 13-Dec-11 17:34pm

My 5, the default example of OOP is shapes. Can't go wrong with that.
Cheers, AT

Sergey Alexandrovich Kryukov 13-Dec-11 19:05pm

Thank you, Addy, but actually it is way to easy to go wrong with that.

This example, developed a bit deeper, will make a classical example of a the "Circle-Ellipse Problem" also known as the "Square-Rectangle Problem".

Please see: http://en.wikipedia.org/wiki/Circle-ellipse_problem.
--SA

Addy Tas 14-Dec-11 1:29am

Hi, i am well aware of that; i also like the explanations on:
http://butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod

Cheers, AT

Sergey Alexandrovich Kryukov 14-Dec-11 13:00pm

That's great. And this page, at first glance, looks like a good collection of related advanced topic.
Cheers,
--SA

JackDingler 14-Dec-11 17:54pm

Kingsoroush wasn't clear, but my interpretation is he's given some code that is used in a switch statement to decide which kind of primitive to draw.

This is a valid way to do so, as is function arrays and function maps.

if you have something like
enum
{
pt_circle, pt_dot, pt_line
} PrimType;

And PrimType is passed as an argument to a create function, then a switch statement is a clean way to decide which object type to instantiate.

Sergey Alexandrovich Kryukov 15-Dec-11 5:56am

There is nothing in the OP's question which indicates that, and the method you show also demonstrate the abuse, not a clean way, I'll explain why. There is the thing: when the code is developed, new classes added, some would need to add a member to your enum. This is not supportable. Moreover, it's easy to extend classes without having access to source code, but impossible with enum, which is not extendable. No, what you suggest is a big "classical" OOP no-no. There are different scenarios which I don't have time to explain. Just picture a vector graphics editor with persistence; you might understand that the switch is never needed. Think how serialization is created; this is the same thing.

The available types are inquired by Reflection and directly attached to the generated, say, menu. When a menu item clicked, appropriate type is instantiated using Reflection. Did you get a picture?
--SA

JackDingler 15-Dec-11 9:34am

If you're dependant on MFC message mapping (menus), you're still dependent on a runtime version of the switch statement.

When a new message comes in, MFC simply scans the array of function pointers looking for a match. The switch statement does the same thing.

The only difference is one is static and the other is runtime.

And the concept of function arrays was being implemented in K&R C code. It isn't something new to C++.

So, since we're talking about vector graphics serialization, how does your example work with the king and master of vector graphics formats, the DXF specification?