Is this So Costly ?

[the one]

Hi,

There is function like
MyFunction( T* apElements, int anCount );
As it can be seen it accepts an array as argument..

In my code, I have a pointer to array ( MyObject** ),
and I need to pass this array to the MyFinction...

If I write like followings in my code, does it becomes a costly operation? I mean, I do de-reference 'a pointer to array' to 'an array'; and the size of array is very large( e.g. 100.000 ); In this case how does 'de-referencing' behave ? Does it dereference all thousands of objects or something else ?

CMain::OnOk()
{
MyObject** pMyObjs;
// create it...
// initialize them..
//...
MyFunction( *pMyObject, 100000 ); // is this de-referencing costly?
}

Thanks...

[Toot]

Simple answer: no. Such is the beauty of C++

Toot

[the one]

Could you please explaine what exactly going around ?

[Yves M]

Originally posted by the one I mean, I do de-reference 'a pointer to array' to 'an array'; and the size of array is very large( e.g. 100.000 );

Not quite. T* as a type is just a pointer to T, it's not an array of T. So you have a T**, which is a pointer to a pointer of T, you dereference it and this will become only a pointer to T.

So the dereference operation only works on the pointer and hence it is quite fast.

[the one]

Thanks Yves M...

I want to be sure about another thing,

I always use (*) as an array instead of ([]) like the example above.

( by saying 'as an array', I mean, I keep starting point of sets... )

Does this usage holds some risks?

[Yves M]

Well, the difference is that with * you can have dynamic arrays at runtime, while you cannot do that with []. The only real danger is that you will have memory leaks or memory overwrites, but that's a common problem for c-style arrays.

If you are writing in C++, I strongly suggest you have a look at std::vector. A good place to start for this is Gabriel's introduction to vector

[Toot]

That's a great article that I will certainly be advising everyone to read. I absolutely agree: STL is both generic and fantastic, but it does have 2 major drawbacks: the documentation is dreadful, hard to find and hard to read; and the code is incredibly hard to read and debug. But that's the price you pay performance, I guess. Of course, you always have a good source of advice...