C# Discussion Boards - CodeProject

Tim Kohler9-Dec-03 6:16

9-Dec-03 6:16

I'm trying to open a file for writing in a server process. I do not want any other process to be able to write to the file while I have it open, but I do want to allow other programs to read from it. Seems simple enough. I think I've done this with CFile in MFC. I'm getting a problem trying to use the .NET FileStream class. Can any of you shed light on why I'm getting a 'File is in use' IO exception with this:

try
{
String Nm = "c:\\testfile.txt";

//simulate the server opening the file for writing:
FileStream str = File.Open(Nm, FileMode.Append, FileAccess.Write, FileShare.Read);

//simulate some other process opening the file for reading: (exception thrown here)
FileStream sss = File.OpenRead(Nm);
}
catch (IOException e)
{
System.Console.WriteLine(e.Message);
}

Re: FileStream question

Heath Stewart9-Dec-03 6:53

Heath Stewart

9-Dec-03 6:53

Actually, you're aren't opening it in a different process so it's not a good test. According to the documentation for the FileShare enum, the file has to be opened in a different process or in a different thread. I tried your code and, of course, got the same error. I open the file in a separate thread and it works fine. Also, pay attention to my finally block in the code below. You should use the finally block in a try-catch (or forget the catch if you want the exception to be thrown to the caller) to make sure things are cleaned up, whether or not an exception is thrown, or even return is called (it is not executed only when the CLR is unloaded, like calling Environment.Exit):

// FileTest.cs
using System;
using System.IO;
using System.Threading;

public class FileTest
{
  public static void Main()
  {
    FileStream s = null;
    try
    {
      s = File.Open("FileTest.cs", FileMode.Open,
        FileAccess.ReadWrite, FileShare.Read);
      new Thread(new ThreadStart(ReadFile)).Start();
    }
    catch (Exception e)
    {
      Console.Error.WriteLine(e.Message);
    }
    finally
    {
      if (s != null) s.Close();
    }
  }

  private static void ReadFile()
  {
    FileStream s = null;
    try
    {
      s = File.OpenRead("FileTest.cs");
      Stream os = Console.OpenStandardOutput(4096);
      int read = 0;
      byte[] buffer = new byte[4096];
      do
      {
        read = s.Read(buffer, 0, buffer.Length);
        os.Write(buffer, 0, read);
      } while (read == buffer.Length);
    }
    catch (Exception e)
    {
      Console.Error.WriteLine(e.Message);
    }
    finally
    {
      if (s != null) s.Close();
    }
  }
}

-----BEGIN GEEK CODE BLOCK-----
Version: 3.21
GCS/G/MU d- s: a- C++++ UL@ P++(+++) L+(--) E--- W+++ N++ o+ K? w++++ O- M(+) V? PS-- PE Y++ PGP++ t++@ 5 X+++ R+@ tv+ b(-)>b++ DI++++ D+ G e++>+++ h---* r+++ y+++
-----END GEEK CODE BLOCK-----

Re: FileStream question

Tim Kohler9-Dec-03 7:17

Tim Kohler

9-Dec-03 7:17

Thanks for the quick response Heath. Try adding a Thread.Sleep after you start that other thread so that the original thread still has the file open for writing. Before moving my stuff to the over simple example I submitted, I had it in different programs altogther. Any other suggestions?

I tried the exact same thing with CFile and it works:

try
{

//open for exclusive write
CStdioFile file;
BOOL bOpen1 = file.Open("C:\\timtest2.txt", CFile::modeWrite | CFile::modeCreate | CFile::shareDenyWrite);
file.WriteString("hi");
file.Flush();

//open a reader
CStdioFile f2;
BOOL bOpen2 = f2.Open("c:\\timtest2.txt", CFile::modeRead | CFile::shareDenyNone);
CString str;
f2.ReadString(str);

//try to open another writer --- this open fails
CStdioFile file3;
BOOL bOpen3 = file3.Open("C:\\timtest2.txt", CFile::modeWrite | CFile::modeCreate | CFile::shareDenyWrite);
file3.WriteString("hi");
file3.Flush();

}
catch (CFileException* pe)
{
pe->ReportError();
pe->Delete();
}

Argh!!

Re: FileStream question

Heath Stewart9-Dec-03 7:28

Heath Stewart

9-Dec-03 7:28

Good point - hadn't thought of that. Blush | :O

Have you tried accessing the file from two different processes? I mean, I would think the same process could access it, but maybe there is a problem related to that.

Re: FileStream question

Tim Kohler9-Dec-03 7:37

Tim Kohler

9-Dec-03 7:37

Well I originally coded it in two processes and that's
when I noticed the problem to begin with. The weird
thing is that other applications (notepad) can open
the files (and they come up in readonly like I would
expect).

I'm totally stumped on what's wrong. I really don't
want to do interop for something so silly.

Re: FileStream question

Tim Kohler10-Dec-03 3:54

Tim Kohler

10-Dec-03 3:54

Heath, I was able to get around this by resorting to interop. I just wrapped a call to the CreateFile function and then instantiated a FileStream object using the file handle (IntPtr) returned from CreateFile. Once I took this route everything works fine. It looks like there's a bug in the FCL when the FileStream class goes to open the files.

Anyway, just an FYI.

thanks again
Tim

Creating XML Documents

MrEyes9-Dec-03 5:28

MrEyes

9-Dec-03 5:28

This thread applies to this board and the XML board, so i tossed a coin and it came here.

I am attempting to create an XML document in C# by parsing values out of a dataset, unfortunately I cannot simply use dataset.WriteXml() as it isnt powerful enough to handle what I need to do.

I understand the basics of using XmlDocument but I am having trouble navigating around the nodes. So if anybody has any guidance or links to related tutorials the assistance would be greatly appreciated.

The following is a basic summary of my problem :

The dataset I am using (and have no control over) has the follow structure :

type value
2 valA
1 valAA
1 valAB
2 valB
1 valBA
1 valBB
1 valBC
2 valC

Now this is structured in such a way that, all the type 2 values are parents, and all the type 1 values directly under it are children of that parent.

Now the XML document I am attempting to create should have the following format :

<data>
 <parent>
  <value></value>
  <child>
   <value></value>
  </child>
 <parent>
</data>

So if I was to produce an XML document using that template and the dataset above I would have the resulting XML :

<data>
 <parent>
  <value>valA</value>
  <child>
   <value>valAA</value>
  </child>
  <child>
   <value>valAB</value>
  </child>
 <parent>
 <parent>
  <value>valB</value>
  <child>
   <value>valBA</value>
  </child>
  <child>
   <value>valBB</value>
  </child>
  <child>
   <value>valBC</value>
  </child>
 <parent>
 <parent>
  <value>valC</value>
  <child>
   <value>valCA</value>
  </child>
 <parent>
</data>

I have managed to get as far as adding the parents to the XML doc, but I am failing when I try to add children to the parent node.

post.mode = signature;
SELECT everything FROM everywhere WHERE something = something_else;
> 1 Row Returned
> 42

Re: Creating XML Documents

MrEyes9-Dec-03 6:02

MrEyes

9-Dec-03 6:02

As usual, I "imaginered" a solution about 10 seconds after asking the question, but I thought I would run it pass you guys as I have a nack for not coming up with the most elegant solutions.

XmlDocument xdoc = new XmlDocument();
xdoc.LoadXml("<?xml version='1.0' encoding='UTF-8'?><data></data>");
XmlNode xnode = xdoc.DocumentElement;
XmlElement xelement;
XmlElement parent = null;
foreach(DataRow row in ds.Tables[0].Rows)
{
	if ((int)row["type"] == 2)
	{
		xelement = xdoc.CreateElement("parent");
		xelement.InnerXml = string.Format("<value>{0}</value>", row["value"].ToString());
		xnode.AppendChild(xelement);

		parent = xelement;
	}
	else
	{
		xelement = xdoc.CreateElement("child");
		xelement.InnerXml = xelement.InnerXml = string.Format("<value>{0}</value>", row["value"].ToString());
		parent.AppendChild(xelement);
	}
}

post.mode = signature;
SELECT everything FROM everywhere WHERE something = something_else;
> 1 Row Returned
> 42

<
>

Re: Creating XML Documents

Heath Stewart9-Dec-03 6:24

Heath Stewart

9-Dec-03 6:24

That's about what I'd do, although you should use the XmlNode methods for creating elements, creating their attributes and assign them values, and assign the values for the elements rather than using string.Format. It works, but there is no validation and it won't take into account namespaces should you ever use them.

You could also create an instance of an XmlTextWriter and use it's methods like WriteStartDocument, WriteStartElement, ... WriteEndElement, and WriteEndDocument. These methods are fully namespace-aware. It basically amounts to writing-out the XML document itself instead of creating one in memory and then writing it.

long path to short path

elena123459-Dec-03 5:12

elena12345

9-Dec-03 5:12

HI,

My program has to trigger a dumb application that won't take paths with spaces. Roll eyes | :rolleyes:

Do you know if there is a built in function in C# that translates long file paths to short file paths.

Thank you,

Elena

Re: long path to short path

Heath Stewart9-Dec-03 6:20

Heath Stewart

9-Dec-03 6:20

There is nothing in the .NET base class library that does this (at least nothing public that I can remember / find), but - if your app runs on Windows 2000 or higher (any NT-based system) - you can P/Invoke the function PathGetShortPath:

[DllImport("shell32.dll", CharSet=CharSet.Unicode)]
public static extern void PathGetShortPath(string path);

You pass the long path into the method and after it returns path contains the short path.

If you need something that works on all operating systems that .NET runs on, you'll have to enumerate each directory and the filename and change it to the 8.3 filename format. It's been a long time since I've worked with these, so you might want to check the PSDK to see if it documents how similarily named files or directories are resolved using the "~N" notation (like "MICROS~1", "MICROS~2", etc.).

You should also trying googling for the solution. I'm sure someone else has had to deal with this before.

Re: long path to short path

Stephane Rodriguez.9-Dec-03 21:24

Stephane Rodriguez.

9-Dec-03 21:24

Does not work on NT. It's only for 2000 and higher.

This API function call works on both OSes : ["kernel32.dll"] GetShortPathName(string szLongPath, string szShortPath, long dwLength).

RSS feed

New to C# Question

Larry J. Siddens9-Dec-03 4:07

Larry J. Siddens

9-Dec-03 4:07

How do you get the XP style using C#?

Larry J. Siddens

Re: New to C# Question

Colin Angus Mackay9-Dec-03 4:35

Colin Angus Mackay

9-Dec-03 4:35

It is not built in unfortunately. However, you have come to the right place. Search CodeProject for XP Style[^] or click the previous link.

--Colin Mackay--

"In the confrontation between the stream and the rock, the stream always wins - not through strength but perseverance." (H. Jackson Brown)

Enumerators in .NET: See how to customise foreach loops with C#

Re: New to C# Question

Heath Stewart9-Dec-03 6:10

Heath Stewart

9-Dec-03 6:10

I wrote an article here: http://www.codeproject.com/csharp/dotnetvisualstyles.asp[^]. If you target .NET 1.1 or higher, you can also call Application.EnableVisualStyles BEFORE you call Application.Run in your entry point (Main). This only works on .NET 1.1 and higher, though, and achieves the same functionality as what I document in my article (which works for .NET 1.0 and higher).

Re: New to C# Question

Larry J. Siddens9-Dec-03 11:29

Larry J. Siddens

9-Dec-03 11:29

Heath,

It was easy to use the Application.EnableVisualSytles() and make sure the controls FlatStyle was "System". Also, It worked in the C++ environment too!

Cool!

Big Grin | :-D

Larry J. Siddens

Re: New to C# Question

Heath Stewart9-Dec-03 11:33

Heath Stewart

9-Dec-03 11:33

Note that C++.NET (Managed C++, or MC++) compiles to the same thing as C#, VB.NET, or any other languages targeting the CLR, so long as your MC++ is written using purely managed code (no mixed mode). This is important to understand: all managed languages compile to (roughly) the same thing: IL. They also have access to the base class library, as well as other assemblies no matter source language they were written in - they all contain IL code.

Re: New to C# Question

Huseyin Altindag9-Dec-03 10:57

Huseyin Altindag

9-Dec-03 10:57

Hi Larry
I think I´ve got something for you
I can send you as attached zip file
email me

Huseyin

First Call to Function does nothing: c#

Goodspeed20029-Dec-03 3:50

Goodspeed2002

9-Dec-03 3:50

I am building an ASP.NET Web site with C#. The design is very much like a portal, where I can load/unload different controls withing the default page. In one of the controls, a user clicks a button to add an item to a "shopping cart", in another control. The first call to my "Add to Cart" function does nothing, however, subsequent clicks on the button work fine.

Any advice on this would be greatly appreciated.

Thanks,
Ben

Re: First Call to Function does nothing: c#

Heath Stewart9-Dec-03 6:08

Heath Stewart

9-Dec-03 6:08

It sounds like you're not loading controls in the right event handlers. There is a specific order to how things are handled (like the Page.Load event fires before a post-back event like a ServerClick or Button.Click event). If you look at some of the events in the SDK documentation for WebControl derivatives, there is a link that describes the order in which events are fired.

Re: First Call to Function does nothing: c#

Goodspeed20029-Dec-03 12:43

Goodspeed2002

9-Dec-03 12:43

Thank you for your response, however I can not seem to find what you suggested in the documentation. Could you be more specific on where I can find this in the SDK documentation?

Thanks a million.

Ben

Re: First Call to Function does nothing: c#

Heath Stewart9-Dec-03 14:13

Heath Stewart

9-Dec-03 14:13

Control Execution Lifecycle[^]

How to validate regular expression pattern?

gokselm9-Dec-03 3:30

gokselm

9-Dec-03 3:30

Hi,

I want to ask a question about Regular expressions.
I want to validate the regular expression pattern if it is written correctly or not? I do not want to test a string against to a regular expression pattern but the regular expression pattern itself.
Is there a way?

Kind Regards

Re: How to validate regular expression pattern?

Heath Stewart9-Dec-03 5:53

Heath Stewart

9-Dec-03 5:53

Just create a new instance of the RegEx. If the regex is invalid, an exception is thrown (this is documented in the class constructor information):

try
{
  Regex re = new Regex("/mypattern/");
  Console.WriteLine("The regular expression is valid.");
}
catch
{
  Console.WriteLine("The regular expression is invalid!");
}

If you move the re declaration outside, you can use it if it's valid after the catch (but then the catch should return or something to keep from trying to use the invalid Regex object).

Re: How to validate regular expression pattern?

gokselm10-Dec-03 11:35

gokselm

10-Dec-03 11:35

Thanks for your help Heath.

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.