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There is an ongoing "discussion" among my colleagues about exactly how a ValueType is stored internally. We are looking for some other views.
If a ValueType is derived from System.Object, does it have a vtable or is it stored in raw form until boxed. In other words, is an System.Int32 stored on the stack as a 4 byte integer or does it have a vtable therby making it larger than 4 bytes?
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The first sentence of the article reads "A Value Type instance on stack without any Method Table ..." Does that mean an System.Int32 is stored on the stack in just 4 bytes (sounds like it to me)?
If so, how does System.ValueType's derivation from System.Object (in which it overides the System.Object methods) avoid a "Method Table?"
Assuming the compiler "changes" a System.Int32 to its 4 byte raw form for storage on the stack, what is the purpose of deriving System.ValueType from System.Object?
Thanks for the article...
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Yes, an integer will only take 4 bytes.
If the "Method table" is needed it will be generated by the CLR on demand. Google boxing and C# for details.
This design allows the lower memryconsumption and faster performance of native types, while still allowing object oriented programming with the native types. The "price" you pay is a performance hit when boxing/unboxing.
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I understand how and why boxing is used...
The question remains: If a System.Int32 occupies only 4 bytes on the stack, what is the purpose of deriving System.ValueType from System.Object?
Thanks for your reply...
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If System.ValueType did not derive from System.Object, how would you make a collection like this one:
System.Collections.Generic.List<System.Object>
which can contain objects of any time - including value types.
If System.ValueType did not derive from System.Object, you would basically need an interface to provide the standard methods (ToString, Hash value, etc)... but to be accessed from an interface the value type would still need to be boxed and now you also need to cast anything derived from System.Object to the interface constantly. So basically nothing was simplified but complexity was added.
Just out of curiosity, what do you think the benefit of NOT deriving from System.Object would be?
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Your explanation implies that System.ValueType has more information than just the raw memory needed to store the data (an 4 byte integer in my previous examples).
I'll try to restate my original question, again using the ValueType System.Int32 as an example:
Does an instance of System.Int32 occupy only 4 bytes in memory when it is allocated on the stack?
If so, what is the purpose of deriving System.ValueType from System.Object if it does not carry any information from System.Object?
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Yes an instance of System.Int32 occupies exactly 4 bytes in memory when it is allocated on the stack.
Yes an instance of System.Int32 is also a System.Object and if the CLR needs its object
behavior, the compiler will have provided the necessary code to make it act as an object,
but that does not change the data foot print.
Example:
int a=12;
string s=a.ToString();
the ToString() method applies to "object" a, the compiler will allocate a 4B integer on stack
and generate code that calls System.Int32.ToString().
Luc Pattyn [Forum Guidelines] [My Articles]
this months tips:
- use PRE tags to preserve formatting when showing multi-line code snippets
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Bravo! That is the best explanation yet.
This is exactly what MOST of my colleagues believe. The devils advocate of the group maintains that:
int a=12; // is not a ValueType until
string s = a.ToString() // is called
Thanks everybody for your input.
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Well, most of your colleagues are right.
It suffices to compile some code and look at the generated MSIL (e.g. with ILDASM)
to observe an int is simply an int, and some class methods get called when appropriate.
Luc Pattyn [Forum Guidelines] [My Articles]
this months tips:
- use PRE tags to preserve formatting when showing multi-line code snippets
- before you ask a question here, search CodeProject, then Google
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I am sorry my answer:
"Yes, an integer will only take 4 bytes."
could leave you in doubt how much memory an integer takes, though I have no idea what so ever how it could be written clearer. And no, my explanation does obviously not imply that more data is stored than the 4 bytes.
I do not know what you mean with "more information available" - yes, obviously it has. Every single object ever created has more information available than the bytes it takes up in memory (as it can easily access the information for the class itself). Or maybe you are referring to the information built into the CLR allowing it to do the boxing/unboxing - sure there is information available for that as well, but obviously per class, not per object, so it does not affect the amount of bytes each object use.
With regards to:
int a=12; // is not a ValueType until
string s = a.ToString() // is called
it probably goes on details in the CLR. "a" is not boxed before the a.ToString call, but at any time "a is ValueType" would return true, and at any time it can be used as a ValueTime. Hence I would consider it a ValueType no matter how it happens to be represented in memory, but I can see the other side of the argument as well - it all comes down to seeing it from the level of C# or from the level of the CLR implementation.
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Also, this is valid:
string s = 12.ToString();
"We make a living by what we get, we make a life by what we give." --Winston Churchill
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And VS will show "Int32" tooltip when you hover over that 12
[ My Blog] "Visual studio desperately needs some performance improvements. It is sometimes almost as slow as eclipse." - Rüdiger Klaehn "Real men use mspaint for writing code and notepad for designing graphics." - Anna-Jayne Metcalfe
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hi friends,
I am building an application in asp.net in which my task is to create a pdf file by using the Adobe Indesign CS2 in asp.net.
I am using the code which is found from the net but on running this is given an error That:
"System.UnauthorizedAccessException: Access is denied."
now tell me about this error and what i have to do to achieve this task.
atleast reply if u don't know the answer also please.......
Here's my code::
Imports System
Imports System.Data
Imports System.Configuration
Imports System.Web
Imports System.Web.Security
Imports System.Web.UI
Imports System.Web.UI.WebControls
' Imports System.Web.UI.WebControls.WebParts
Imports System.Web.UI.HtmlControls
Imports InDesign
Public Class _Default
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim cstrInddFile As String = Server.MapPath("~/Archieve/yourstory_backcover1.indd")
Dim cstrXMLFile As String = Server.MapPath("~/Archieve/xml1.xml")
Dim cstrOutputFile As String = Server.MapPath("~/Archieve/out.pdf")
Dim indAppType As Type = Type.GetTypeFromProgID("InDesign.Application")
Dim objInDesign As InDesign.Application = DirectCast(Activator.CreateInstance(indAppType, True), InDesign.Application)
Dim objDoc As InDesign.Document = DirectCast(objInDesign.Open(cstrInddFile, False), InDesign.Document)
objDoc.ImportXML(cstrXMLFile)
Dim objPreset As InDesign.PDFExportPreset=DirectCast(objInDesign.PDFExportPresets.LastItem(),InDesign.PDFExportPreset)
objDoc.Export(idExportFormat.idPDFType, cstrOutputFile, False, objInDesign.PDFExportPresets("Press"))
End Sub
End Class
-- modified at 7:21 Thursday 18th October, 2007<b></b>
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gopal_Pandey wrote: this is really urgent one
It's always urgent. Still kudos for not putting urgent in your post title.
Anyway - your problem here is that the user that the website is running under doesn't have access to the file. This is down to permission restrictions - so you need to allow the website user (that's the user identity the website runs under) read/write permissions on the relevant directory.
Deja View - the feeling that you've seen this post before.
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Please don't email me direct. Doing this prevents others from following the thread.
Anyway - to answer your question, I have already given you a hint as to what to do. Check the permissions of the directory and see whether or not the ASP worker process has read/write access to it. I don't know how much more explicit I can be without actually coming round and doing it for you.
Deja View - the feeling that you've seen this post before.
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Hi everyone,
Sorry for that Email Mr Pete O'Hanlon,
I got your answers but all of you telling me only one solution which i have solved out i have given access to that file and also allowed the whole files to access rights what u have told me but it doesn't solve any problems....
I am using a trial version which is not registered of Adobe Indesign CS2.....
Please think again about this and reply me
i am waiting for your answers.......
bye........
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Hi Friends,
Using .NET 2.0 how do I extract .zip file? It seems GZipStream does not go well. Is there any other class in .NET where in can be used to extract .zip file?
Thanx in advance.
Regards,
Vipul Mehta
Sr. Software Engineer
Accenture Services Pvt Ltd
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Thanx for the links but I am suppose to use microsoft class liabraries only.
Regards,
Vipul Mehta
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Hi,
In the java.utils.zip include tools that should help JAVA developers in .NET
But, one of the grate features there, that i can't understand why it isn't part of the common BCL is the zip file support.
First, add vjslib.dll and vjslibcw.dll as reference.
If you can't find them, ther are in J# Package: Here[^].
Use ZipFile Class to zip and unzip files.
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Hi,
After implementing the following logic I get "The magic number in GZip header is not correct. Make sure you are passing in a GZip stream." error
string sourceFile = @"C:\Test\MyDocs.zip";
string destinationFile = @"C:\Test";
if (File.Exists(sourceFile) == false)
{
return;
}
FileStream sourceStream = null;
FileStream destinationStream = null;
GZipStream decompressedStream = null;
byte[] quartetBuffer;
int position;
int checkLength;
byte[] buffer;
try
{
sourceStream = new FileStream(sourceFile, FileMode.Open);
decompressedStream = new GZipStream(sourceStream, CompressionMode.Decompress, true);
quartetBuffer = new Byte[4];
position = Convert.ToInt32(sourceStream.Length) - 4;
sourceStream.Position = position;
sourceStream.Read(quartetBuffer, 0, quartetBuffer.Length);
sourceStream.Position = 0;
checkLength = BitConverter.ToInt32(quartetBuffer, 0);
buffer = new byte[checkLength + 100];
int offset = 0;
int total = 0;
while (true)
{
int bytesRead;
bytesRead = decompressedStream.Read(buffer, offset, 100);
if (bytesRead == 0)
{
break;
}
else
{
offset += bytesRead;
total += bytesRead;
}
}
// Now write everything to the destination file
destinationStream = new FileStream(destinationFile, FileMode.Create);
destinationStream.Write(buffer, 0, total);
// and flush everyhting to clean out the buffer
destinationStream.Flush();
}
catch (Exception ex)
{
}
finally
{
// Make sure we allways close all streams
if (sourceStream != null)
{
sourceStream.Close();
}
if (decompressedStream != null)
{
decompressedStream.Close();
}
if (destinationStream != null)
{
destinationStream.Close();
}
}
Can any body help me out?
Regards,
Vipul Mehta
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Are you absolutely sure your .zip file is in gzip format? The gzip format has a header and the GZipStream class accounts for this. But, if your .zip file is not in gzip format, the gzip decompression will not work.
Your .zip file may have been created with the DEFLATE compression method in which case you need to use the DeflateStream class.
Simply substitute GZipStream with DeflateStream and see what happens...
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I am trying to unzip an container .zip file (it contains many files & folder within that). My app. downloads this .zip file from an http URL of an web site & then tries to unzip it.
After implementing DeflateStream class, it shows me following error:
"Block length does not match with its complement"
Regards,
Vipul Mehta
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ZIP is not GZip. They are different formats. GZip compresses a single stream of bytes, ZIP is a container for multiple files each of which can be compressed a different way (although conventionally the Deflate algorithm is used, unless that gives no compression in which case the original file is simply stored instead).
The ZIP format is documented[^]. Parsing it is actually pretty easy.
SharpZipLib does work but I've found it pretty slow.
The GZipStream and DeflateStream classes are primarily intended for the web support e.g. HttpWebRequest, because the HTTP protocol allows responses to be compressed. Java has ZIP classes because its class library format, JAR, is simply a renamed ZIP file. (An individual class's bytecode is stored in a .class file, early versions of Java did not allow you to bundle these up into a package, later versions added the Java ARchive, JAR, format.)
DoEvents: Generating unexpected recursion since 1991
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