Re: Array of value types

From: Dennis Myrén (dennis_at_oslokb.no)
Date: 10/06/04 

Date: Wed, 6 Oct 2004 13:34:11 +0200

OK. Thanks Richard. 

-- 
Regards,
Dennis JD Myrén
Oslo Kodebureau
"Richard Blewett [DevelopMentor]" <richardb@develop.com> wrote in message 
news:%23uhNXg5qEHA.1296@TK2MSFTNGP12.phx.gbl...
> Yes
>
> Regards
>
> Richard Blewett - DevelopMentor
> http://staff.develop.com/richardb/weblog
>
> 
> nntp://news.microsoft.com/microsoft.public.dotnet.languages.csharp/>
>
> Just one more question regarding value types;
> consider this snippet:
> foreach (IFDENTRY e in ifd.entries)
> {
> ...
> }
>
> Given that IFDENTRY is a structure, and ifd.entries is a field of type
> System.Array
> of type IFDENTRY, is this causing a copy as well for each item in the 
> array?
>
> --
> Regards,
> Dennis JD Myr?n
> Oslo Kodebureau
> "Jon Skeet [C# MVP]" <skeet@pobox.com> wrote in message
> news:MPG.1bcc948f778b2a9898b5b9@msnews.microsoft.com...
> Dennis Myr?n <dennis@oslokb.no> wrote:
> > >Does it really need to be a structure then?
> > Well, i thought so...
> > The structure directly represents a chunk of a binary file.
> > I use:
> > [ StructLayout( LayoutKind.Sequential, Pack = 0x1 ) ]
> > to explicitly specify that the order is essential.
> > I use System.Runtime.InteropServices.Marshal class
> > to create the structure instance from a byte array.
> > Quite embarrasing, I was sure the StructLayout attribute could only
> > be applied to structures, but as i tested making it a class now, it
> > still compiles without errors.
>
> I wouldn't like to say whether you can still do it, to be honest.
> Interop is far from a specialty of mine :(
>
> However, if you have an array of references, you *probably* won't be
> able to pass that as an array of that type by interop, because the data
> won't be in the right place. Ask in the interop group for more
> information.
>
> On the other hand, if you're going to pass all of this via interop
> anyway, then it's probably not going to be that much of an issue doing
> the in-memory copy to start with.
>
> > >> My option might be to, rather than assigning the elements,
> > >> to use the array directly with indexing(a lot of indexing then):
> > >>
> > >> STRUCT [] a = new STRUCT [0xA];
> > >> a [0x0].PROPERTY = 0x0;
> >
> > >Yes, you could do that - but if you're going to set any significant
> > >number of properties, wouldn't you be better off with a copy anyway?
>
> > Just out of interest, where would the breakpoint(array index accesses)
> > be where to rather do a copy than working with array indices
> > (i can test this by myself though, just if you already know a good
> > answer)?
>
> I don't know of anything like that - it's just a case of balancing the
> convenience of copying the whole structure in one go with the
> increasingly marginal performance benefits of using indexing.
>
> --
> Jon Skeet - <skeet@pobox.com>
> http://www.pobox.com/~skeet
> If replying to the group, please do not mail me too
>
>
>
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