class and functions

[lord loh]

What is the difference if I make a class with functions

Or

If I make a file with only functions and no class defn. and just include the file when I need?

I generally do not use all functions of a class. So are there any memory/speed related advandages?

Is there any other advantage of a class other than grouping functions ?

[Manish Malik]

I assume you are talking C++, but you can translate the concepts to other OO languages too. I suggest you take a look at what a 'namespace' is. If your only requirement is to keep a bunch of functions that do not require to operate on some objects (depends on your program design), then you should be using a namespace to wrap them up. e.g.

-- myincludefile.h


#pragma once
// replace #pragma once with include guards if you are using compilers other than VC++ and gcc that do no support this directive

namespace myABClibrary
{
void myfunction1() { }
void myfunction2() { }
};



-- main.cpp


#include "myincludefile.h"

int main()
{
myABClibrary::myfunction1();
return 0;
}



or even

-- main.cpp


#include "myincludefile.h"

int main()
{
using myABClibrary;

myfunction1();

return 0;
}




Classes are used when you have designed your program (or a part of it) in terms of objects, that have members and methods that operator on them. Not suited for the job when all you require is to keep a library of few functions. Though if the size of the library grows more than that, you are better off redesigning a bit to effectively utilize a combination of namespaces and classes.

[lord loh]

Can you point a link toward knowing more about name space.(I was not talking about c++ though!)

And I also wanted to know about speed/memory usage of class. Is it better to include a function and use it as and when required (at run time)?

Thank You!

[bfarley]

If you were not taliking about C++, the point is moot. No functions can exist outside a class in C#.

Bill F

[lord loh]

huh! :rolleyes:
I was not talking about C# either. It was php I was thinking of...

[ergas]

If you can use a function, there is no reason not to use it concerning speed/memory, specially if you run your app on some PC.

Here is a sample, why to use class member function:
Suppose you have drawing function that takes CShape argument:
Draw( CShape *shape)
{
if( shape == "Circle" ) DrawCircle( shape );
else if( shape == "square" ) DrawSquare( shape );
}

In the sample above it is reasonable to make virtual DrawMe() member of CShape class.
Sometimes it may be better to use a function to perform some simple task.

[lord loh]

Yes! I agree that functions are very very useful....but why put it in a class? it could be a function outside a class...if the language constructs permit so...(bfarley pointed out about the C#)...

I am really trying to understand "why use classes ?" when simple function do...

[ergas]

In my little sample above there is pointed out, why to use class.

1. Use a class-member:
If some function have to check the object type, and then to take different actions, that is a classic example to use a class-member function.

2. Use a function
If the function is object-type independant, then there may be no reason to make it as a member of some class.

3. There is a lot more, like protection-issues. If a function is used only for one class, it is a good practice to make it a private member of this class.