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How to compare MemoryStream?

5-Jul-04 10:08

You just have to recurse and construct the "path" yourself. This would be a very simple recursive loop to create.

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god4k5-Jul-04 5:57

god4k

5-Jul-04 5:57

Dear, Sir and Madam.

To compare integer use the following code
if (i==j) //i and j is integer
DoSomething();

If i and j is MemoryStream, how to compare them

Sorry for bad English.
Thank You.

Heath Stewart5-Jul-04 10:01

5-Jul-04 10:01

Only primitive types and those that define the equality operators are comparable using ==, otherwise a simple reference (whether i and j referenece the same object) is performed. Classes may also override Object.Equals; if they don't, again simple reference equality is used.

Since MemoryStream nor its base class, Stream, define either of these, you must compare these byte-for-byte yourself:

public int Compare(MemoryStream a, MemoryStream b)
{
  if (a == null && b == null) return 0;
  else if (a == null || b == null) throw new ArgumentNullException(
    a == null ? "a" : "b");
  if (a.Length < b.Length) return -1;
  else if (a.Length > b.Length) return 1;
  byte buf;
  while ((buf = a.ReadByte()) >= 0)
  {
    int diff = buf.CompareTo(b.ReadByte());
    if (diff != 0) return diff;
  }
  return 0;
}

As with most comparisons in the BCL, 0 is returned if the two streams are equal. a negative or positive integer value is returned depending on the conditions, which should be obvious from the code above.

Note that this is only an example, but should give you an idea of how to compare the MemoryStreams.

You could also P/Invoke the memcmp function, although this will hinder the portability of your code but will be very fast.

As I covered a few days ago with the same question (hint: it's a good idea to try searching for previous questions before posting), you can P/Invoke memcmp like so:

public sealed class ByteComparer
{
  private ByteComparer();
  public static int Compare(byte[] a, byte[] b)
  {
    return memcmp(a, b, new IntPtr(a.Length)).ToInt32();
  }
  [DllImport("msvcrt.dll")]
  private static extern IntPtr memcmp(byte[] a, byte[] b, IntPtr count);
}

This does a comparison using the native memcmp API if you just pass two byte[] arrays (which you can get easily using MemoryStream.ToArray) into the static method Compare:

MemoryStream a = ...;
MemoryStream b = ...;
int diff = ByteComparer.Compare(a.ToArray(), b.ToArray());

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Mike Dimmick5-Jul-04 13:44

Mike Dimmick

5-Jul-04 13:44

It might be worth adding:

if( a == b )
   return 0;

in case anyone does try to do Compare( a, a ). It might seem unlikely, but you have to consider aliasing.

Stability. What an interesting concept. -- Chris Maunder

Heath Stewart5-Jul-04 17:58

5-Jul-04 17:58

Good idea. Might save quite a bit of time since the byte for byte comparison would run max(O(n)) just to return 0.

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Re: How to add custom properties in PropertyGrid at Runtime

god4k5-Jul-04 14:30

god4k

5-Jul-04 14:30

Thank you.

Heath Stewart5-Jul-04 5:11

Howto Delete a file at run time!?!

5-Jul-04 5:11

First of all, this is best suited for a good abstract model. A Person class, for example, would define the common properties and derivative classes (like Executive, Manager, etc.) would define additional properties specific to them (perhaps even extend Person with a Supervisor class, and the latter two classes derive from Supervisor since they would ultimately have something in common).

If you want the PropertyGrid to display properties at runtime that aren't actually defined on the class, implement the ICustomTypeDescriptor on your class. For the most part, just call TypeDescriptor methods for each interface member implementation, passing true for the parameter typically called noCustomTypeDesc. For example:

// Using explicit interface implementations to hide
// all the methods that shouldn't be called directly
TypeConverter ICustomTypeDescriptor.GetConverter()
{
  return TypeDescriptor.GetConverter(this, true);
}

For the two ICustomTypeDescriptor.GetProperties overloads, you return a PropertyDescriptorCollection with the defined properties and shadowed properties.

You can find more information about the ICustomTypeDescriptor in the .NET Framework SDK, but implementing will require understanding the .NET ComponentModel, so I suggest you read Enhancing Design-Time Support[^] in the .NET Framework SDK.

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QzRz5-Jul-04 4:45

5-Jul-04 4:45

Hello...

I have a problem...

I want to delete a file but i cant delete it, it thwors an error an sais acces denied!

I have tried this...

string FileFullDest = "C:\test\test.dl";
FileInfo Delete = new FileInfo(FileFullDest);
Delete.Delete();

Don't know what else to do!

Anyone who can help me?

Heath Stewart5-Jul-04 4:50

5-Jul-04 4:50

You can also use File.Delete, but the result is the same if you don't have the necessary file system permissions (for that particular file) or code access security (i.e., permission to delete any file via code in .NET).

Please be more descriptive. What is the exact exception type (ex: SecurityException, etc.) and message text? From where is the application that contains this code run (i.e., local computer, intranet server, etc.)?

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QzRz5-Jul-04 5:09

5-Jul-04 5:09

it trows an IOException!
it sais -> the process cannot access the file "c:\test\test.dll" because it is being used by another process!

But isn't it possible to delete it anyway?

Heath Stewart5-Jul-04 5:12

5-Jul-04 5:12

Not if another process is using it, no. Whatever process has loaded and mapped test.dll into its process space must be shutdown first. Operating systems are supposed to protected against this.

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QzRz5-Jul-04 5:15

5-Jul-04 5:15

And there is no way to stop the process at run time?

Heath Stewart5-Jul-04 5:19

5-Jul-04 5:19

Yes, but you have to know what the process is. You also shouldn't just go stopping processes just so you can delete a file.

See the System.Diagnostics.Process class for a way to get a list of running processes. You'd have to enumerate them and then enumerate their Process.Modules property to find which process is using test.dll, then attempt to close it gracefully using Process.Close. If that doesn't work, use Process.Kill to terminate it.

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QzRz5-Jul-04 5:25

5-Jul-04 5:25

okay i try that!!

thansk!!

Colin Angus Mackay5-Jul-04 5:57

Colin Angus Mackay

5-Jul-04 5:57

I sense impending disaster.

QzRz5-Jul-04 9:53

5-Jul-04 9:53

what do you mean?

Jeremy Falcon5-Jul-04 10:14

Jeremy Falcon

5-Jul-04 10:14

That you're trying to make a malicious program.

Jeremy Falcon

Object reference not set to an instance of an object

Colin Angus Mackay5-Jul-04 11:06

Colin Angus Mackay

5-Jul-04 11:06

Actually, it was more to do with the fact that he appeared to blindly ignore some of Heath's advice.

Heath Stewart wrote:
You also shouldn't just go stopping processes just so you can delete a file.

After giving this warning, Heath answered the question to which
QzRz wrote:
okay i try that!!

"You can have everything in life you want if you will just help enough other people get what they want." --Zig Ziglar

The Second EuroCPian Event will be in Brussels on the 4th of September

Can't manage to P/Invoke that Win32 API in .NET? Why not do interop the wiki way!

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rturner0035-Jul-04 4:34

rturner003

5-Jul-04 4:34

I am using the article Inserting XML formatted data into SQL Server 2000 By faisal abdul aziz as a template for some work I doing. I have create a class, in a separate class file, to cover the 'child' elements. I have called this Answers.cs.

The begining of the file looks like this:

using System;
using System.Xml.Serialization;

namespace SGC.Apps.Consultations
{

public class Answers
{
public Answers()
{
}

private int intQNo;
private int intAns;

[XmlAttribute]
public int Question_No {
get {
return this.intQNo;
}
set {
intQNo = value;
}
etc.....

In web form I have button_click event routine
private void Button1_Click(object sender, System.EventArgs e) {
if (Page.IsValid) {
XmlSerializer serlizer = new XmlSerializer(typeof(Replies));
int intCount = 2;
Answers[] ans = new Answers[intCount];
ans[1].Question_No = 3;

etc......

I get the error Object reference not set to an instance of an object
The highlighted line is 'ans[1].Question_No = 3;

Full error is [NullReferenceException: Object reference not set to an instance of an object]

Can anyone help with what stupid thing I am doing wrong?

cheers

Robert T Turner
South Gloucestershire Council

Re: Object reference not set to an instance of an object

Colin Angus Mackay5-Jul-04 4:43

Colin Angus Mackay

5-Jul-04 4:43

1: int intCount = 2;
2: Answers[] ans = new Answers[intCount];
3: ans[1].Question_No = 3;

I've numbered the lines above.

In line 2 all you are doing is reserving the space for the objects. You still have to create them. So after line 2 you need to do

ans[0] = new Answer();

Also, remeber that indexes in C# are zero-based. I don't know if you knew that, but it looked odd (line 3) that you were starting on index 1.

Re: Object reference not set to an instance of an object

Heath Stewart5-Jul-04 4:53