C# Frequently Asked Questions : .NET Framework

How do I calculate a MD5 hash from a string?

CSharpFAQ — Tue, 10 Oct 2006 02:15:00 GMT

It is a common practice to store passwords in databases using a hash. MD5 (defined in RFC 1321) is a common hash algorithm, and using it from C# is easy.

Here’s an implementation of a method that converts a string to an MD5 hash, which is a 32-character string of hexadecimal numbers.

public string CalculateMD5Hash(string input)
{
    // step 1, calculate MD5 hash from input
    MD5 md5 = System.Security.Cryptography.MD5.Create();
    byte[] inputBytes = System.Text.Encoding.ASCII.GetBytes(input);
    byte[] hash = md5.ComputeHash(inputBytes);
 
    // step 2, convert byte array to hex string
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < hash.Length; i++)
    {
        sb.Append(hash[i].ToString("X2"));
    }
    return sb.ToString();
}

An example call:

string hash = CalculateMD5Hash("abcdefghijklmnopqrstuvwxyz");

…returns a string like this:

C3FCD3D76192E4007DFB496CCA67E13B

To make the hex string use lower-case letters instead of upper-case, replace the single line inside the for loop with this line:

sb.Append(hash[i].ToString("x2"));

The difference is the ToString method parameter.

[author: Jani Järvinen, C# MVP]

How do I play default Windows sounds?

CSharpFAQ — Tue, 28 Mar 2006 05:03:00 GMT

Sometimes, you might want to make your application a bit more audible. If you are using .NET 2.0, you can utilize the new System.Media namespace and its SystemSound and SystemSounds classes.

The SystemSounds class contains five static properties that you can use to retrieve instances of the SystemSound class. This class in turn contains the Play() method, which you can use to play the wave file associated with the sound in Windows Control Panel. Note that the user can also disable all sounds altogether, which would mean that no sound can be heard through the computer speakers.

To play for example the classical beep sound, you could use the following code:

System.Media.SystemSounds.Beep.Play();

Similarly, you could play the “Question” sound with this code:

System.Media.SystemSounds.Question.Play();

The System.Media namespace is defined in System.dll, so there are no new DLLs you would need to add to your project’s references to use the above code.

[author: Jani Järvinen, C# MVP]

Where can I find design and coding guidelines for .NET?

CSharpFAQ — Mon, 21 Feb 2005 21:30:00 GMT

tipu_77 asked "What are microsoft suggested naming conventions in C#?"

The .NET Framework Team collects their recommendations at their

GotDotNet community site.

which points to a fairly comprehensive MSDN page

Design Guidelines for Class Library Developers.

which includes the section Naming Guidelines

[Author: SantoshZ]

How do I get and set Environment variables?

CSharpFAQ — Thu, 02 Dec 2004 17:01:00 GMT

Use the System.Environment class.
Specifically the GetEnvironmentVariable and SetEnvironmentVariable methods.

Admitedly, this is not a question specific to C#, but it is one I have seen enough C# programmers ask, and the ability to set environment variables is new to the Whidbey release, as is the EnvironmentVariableTarget enumeration which lets you separately specify process, machine, and user.

Brad Abrams blogged on this way back at the start of this year, and followed up with a solution for pre-Whidbey users.

[Author: SantoshZ]

What is the equivalent to regsvr32 in .NET?

CSharpFAQ — Mon, 02 Aug 2004 21:15:00 GMT

Where you once used Regsvr32 on unmanaged COM libraries, you will now use Regasm on managed .NET libraries.

“Regsvr32 is the command-line tool that registers .dll files as command components in the registry“

“Regasm.exe, the Assembly Registration tool that comes with the .NET SDK, reads the metadata within an assembly and adds the necessary entries to the registry, which allows COM clients to create .NET Framework classes transparently. Once a class is registered, any COM client can use it as though the class were a COM class. The class is registered only once, when the assembly is installed. Instances of classes within the assembly cannot be created from COM until they are actually registered.“

If you want to register an assembly programmatically, see the RegistrationServices class and ComRegisterFunctionAttribute

How can I run another application or batch file from my Visual C# .NET code?

CSharpFAQ — Wed, 02 Jun 2004 06:54:00 GMT

Posted by: Duncan Mackenzie, MSDN
This post applies to Visual C# .NET 2002/2003

Suppose you want to run a command line application, open up another Windows program, or even bring up the default web browser or email program... how can you do this from your C# code?

The answer for all of these examples is the same, you can use the classes and methods in System.Diagnostics.Process to accomplish these tasks and more.

Example 1. Running a command line application, without concern for the results:

private void simpleRun_Click(object sender, System.EventArgs e){
 System.Diagnostics.Process.Start(@"C:\listfiles.bat");
}

Example 2. Retrieving the results and waiting until the process stops (running the process synchronously):

private void runSyncAndGetResults_Click(object sender, System.EventArgs e){
 System.Diagnostics.ProcessStartInfo psi =
   new System.Diagnostics.ProcessStartInfo(@"C:\listfiles.bat");
 psi.RedirectStandardOutput = true;
 psi.WindowStyle = System.Diagnostics.ProcessWindowStyle.Hidden;
 psi.UseShellExecute = false;
 System.Diagnostics.Process listFiles;
 listFiles = System.Diagnostics.Process.Start(psi);
 System.IO.StreamReader myOutput = listFiles.StandardOutput;
 listFiles.WaitForExit(2000);
 if (listFiles.HasExited)
  {
  string output = myOutput.ReadToEnd();
  this.processResults.Text = output;
 }
}

Example 3. Displaying a URL using the default browser on the user's machine:

private void launchURL_Click(object sender, System.EventArgs e){
 string targetURL = @http://www.duncanmackenzie.net;
 System.Diagnostics.Process.Start(targetURL);
}

In my opinion, you are much better off following the third example for URLs, as opposed to executing IE with the URL as an argument. The code shown for Example 3 will launch the user's default browser, which may or may not be IE; you are more likely to provide the user with the experience they want and you will be taking advantage of the browser that is most likely to have up-to-date connection information.

C# code download available from http://www.duncanmackenzie.net/Samples/default.aspx

By the way, this post is a simple port of an earlier VB FAQ post... just in case you thought you had seen it already in your feeds...