by Charlie Calvert

A common need for programmers is to get the users home directory and other commonly used directories. In .NET, this involves using a combination of the Environment.SpecialFolders enumeration, and the Environment.GetEnvironmentVariable() function. The code in this article is written in C#, but it should be easy to translate it into Pascal code.

Special Folders

Here is the Environment.SpecialFolder enumeration:

	Environment.SpecialFolder.ApplicationData
	Environment.SpecialFolder.System
	Environment.SpecialFolder.CommonApplicationData
	Environment.SpecialFolder.CommonProgramFiles
	Environment.SpecialFolder.Cookies
	Environment.SpecialFolder.Desktop
	Environment.SpecialFolder.DesktopDirectory
	Environment.SpecialFolder.Favorites
	Environment.SpecialFolder.History
	Environment.SpecialFolder.InternetCache
	Environment.SpecialFolder.LocalApplicationData
	Environment.SpecialFolder.MyComputer
	Environment.SpecialFolder.MyMusic
	Environment.SpecialFolder.MyPictures
	Environment.SpecialFolder.Personal
	Environment.SpecialFolder.ProgramFiles
	Environment.SpecialFolder.Programs
	Environment.SpecialFolder.Recent
	Environment.SpecialFolder.SendTo
	Environment.SpecialFolder.StartMenu

Here is how to use this enumeration:

 String PersonalFolder = 
	Environment.GetFolderPath(Environment.SpecialFolder.Personal);

After executing this code, the variable PersonalFolder should contain the value of your My Documents directory.

Special Folders, Integer value of Enum, Dir on My System

In Listing 1 you see the values of all the special folders on my system. Note that this enumeration is not sequential. In particular, the integer value for the first member of the enumeration in .NET 1.1 is 0, the next is 2, then 5, then 6, etc. I got these values by writing this code: int i = (int)sp. If someone sees a pattern here, let me know!

Listing 1: The values of the SpecialFolder enumeration on my system. The number in the first column is the integer value of the particular SpecialFolder member shown in the second column.

0	Desktop			C:\Documents and Settings\Charlie\Desktop
2	Programs		C:\Documents and Settings\Charlie\Start Menu\Programs
5	Personal		D:\documents
6	Favorites		C:\Documents and Settings\Charlie\Favorites
8	Recent			C:\Documents and Settings\Charlie\Recent
9	SendTo			C:\Documents and Settings\Charlie\SendTo
11	StartMenu		C:\Documents and Settings\Charlie\Start Menu
13	MyMusic			D:\documents\My Music
16	DesktopDirectory	C:\Documents and Settings\Charlie\Desktop
17	MyComputer			 
26	ApplicationData		C:\Documents and Settings\Charlie\Application Data
28	LocalApplicationData	C:\Documents and Settings\Charlie\Local Settings\Application Data
32	InternetCache		C:\Documents and Settings\Charlie\Local Settings\Temporary Internet Files
33	Cookies			C:\Documents and Settings\Charlie\Cookies
34	History			C:\Documents and Settings\Charlie\Local Settings\History
35	CommonApplicationData	C:\Documents and Settings\All Users\Application Data
37	System			C:\WINDOWS\System32
38	ProgramFiles		C:\Program Files
39	MyPictures		D:\documents\My Pictures
43	CommonProgramFiles	C:\Program FilesCommon Files

Listing 2 shows the code for getting the values found in the previous listing. Note the use of the IList interface to access the list of strings stored in a ListBox. Becoming comfortable with interfaces is one of the core tasks for programmers migrating from Win32 to .NET. Java programmers should already be familiar with this paradigm.

Listing 2: The code for retrieving the values displayed in Listing 1.

	private static void ShowSpecialFolder(Environment.SpecialFolder sp, IList list)
	{
		int i = (int)sp;		
		String S1 = String.Format("{1} {0} {2} {0}{0}{0} {3}", '\t', i,
			sp.ToString(), Environment.GetFolderPath(sp));
		list.Add(S1);			
	}

	public static IList GetAllSpecialFolders(IList list)
	{
		ShowSpecialFolder(Environment.SpecialFolder.ApplicationData, list);
		ShowSpecialFolder(Environment.SpecialFolder.System, list);
		ShowSpecialFolder(Environment.SpecialFolder.CommonApplicationData, list);
		ShowSpecialFolder(Environment.SpecialFolder.CommonProgramFiles, list);
		ShowSpecialFolder(Environment.SpecialFolder.Cookies, list);
		ShowSpecialFolder(Environment.SpecialFolder.Desktop, list);
		ShowSpecialFolder(Environment.SpecialFolder.DesktopDirectory, list);
		ShowSpecialFolder(Environment.SpecialFolder.Favorites, list);
		ShowSpecialFolder(Environment.SpecialFolder.History, list);
		ShowSpecialFolder(Environment.SpecialFolder.InternetCache, list);
		ShowSpecialFolder(Environment.SpecialFolder.LocalApplicationData, list);
		ShowSpecialFolder(Environment.SpecialFolder.MyComputer, list);
		ShowSpecialFolder(Environment.SpecialFolder.MyMusic, list);
		ShowSpecialFolder(Environment.SpecialFolder.MyPictures, list);
		ShowSpecialFolder(Environment.SpecialFolder.Personal, list);
		ShowSpecialFolder(Environment.SpecialFolder.ProgramFiles, list);
		ShowSpecialFolder(Environment.SpecialFolder.Programs, list);
		ShowSpecialFolder(Environment.SpecialFolder.Recent, list);
		ShowSpecialFolder(Environment.SpecialFolder.SendTo, list);
		ShowSpecialFolder(Environment.SpecialFolder.StartMenu, list);

		return list;
	}

	private void button1_Click_1(object sender, System.EventArgs e)
	{
		GetAllSpecialFolders(listBox1.Items);
	}

This code begins with the last method, button1_Click_1, which will be called when the user clicks on a button. The button click method calls the GetAllSpecialFolders() method. GetAllSpecialFolders() has one call to ShowSpecialFolders for each of the special folders that the C# API tracks for you. Each call to ShowSpecialFolders creates one of the strings shown in Listing 1:

0	Desktop			C:\Documents and Settings\Charlie\Desktop

The ShowSpecialFolders method begins by getting the integer value of the member of the SpecialFolders enumeration that is passed in as a parameter:

 int i = (int)sp; 

This integer value appears at the beginning of the strings shown in Listing 1. For instance, it is the 0 before the word Desktop. This value is normally not important to developers, but I am showing it to you in case you are curious about the declaration of the SpecialFolders enumeration.In Microsoft's implementation of C#, we never see the source, so it is interesting to guess how it must be declared. For instance, in this case, the enumeration might look something like this:

enum SpecialFolder {Desktop=0, Programs=2, Personal=5, Favorites=6, Recent=8, etc);

The next line of my ShowSpecialFolders method begins with a call to String.Format. The String.Format() method has a peculiar, but useful, syntax I have only seen in C#. Each of the instances of code that appears in curly braces is replaced by one of the latter parameters passed to the method. For instance {0}, {1} and {2} get replaced with one of the parameters such as '\t' or sp.ToString() which is passed to String.Format. Note that '\t;' is the second parameter. It is the tab character, and will replace all instances of {0}. The variable i is the third parameter, and the value stored in that variable will replace each instance of {1}.

The code {2} is replaced by each instance of sp.ToString(). sp is a member of the SpecialFolder enumeration, and the ToString() method conveniently converts sp into a string representation of the enumeration member. That is, it converts sp into a string such as "Desktop", "Programs", "Personal", etc. In the String shown above, the value of i appears as 0, and sp.ToString() appears as Desktop. Again, programmers don't normally need to make a call to find out the string value of an enumeration, but it is interesting to know that you can do it if you so desire.

The last parameter, the one that goes into {3}, is the path, such as C:\Documents and Settings\Charlie\Desktop. I retrieved the path string by making the following call: Environment.GetFolderPath(sp). Note that I place three tabs in front of the path, to separate it from the rest of the code:

String S1 = String.Format("{1} {0} {2} {0}{0}{0} {3}", 't', i,
	sp.ToString(), Environment.GetFolderPath(sp));

I still had to manually edit some of the tabbing to make it come out as evenly as it appears in Listing 1.

Useful Methods

Listing 3 shows some other useful methods. Note that I use the GetEnvironmentVariable call to retrieve the Home Directory and in the call to GetEnvTempDir(). Since environment variables are mutable, these calls are probably less reliable than other calls. Also, they may be OS dependant. In particular, I have only tested them on XP. Note, however, the GetTempDir() call, which uses what should be a more reliable method of retreiving the temporary directory. In particular, it uses the Path object. The GetMyDocumentsDir() method is a wrapper around the Environment.SpecialFolder enumeration.

Listing 3: Routines for getting the users home directory, their My Documents directory, and the temp directory.

	public static String GetHomeDir()
	{
		return Environment.GetEnvironmentVariable("USERPROFILE");
	}

	public static String GetMyDocumentsDir()
	{
		return Environment.GetFolderPath(Environment.SpecialFolder.Personal);
	}

	public static String GetEnvTempDir()
	{
		return Environment.GetEnvironmentVariable("TEMP");
	}

	public static String GetTempDir()
	{
		return System.IO.Path.GetTempPath();
	}

Summary

In this article you have learned a few simple tricks for getting system dependant information while using .NET. In particular, you learned about the Environment.SpecialFolder enumeration, and about the Environment.GetEnvironmentVariable method. The Environment class is part of the System namespace, so you should not have to add any special Using statements to your code other than the default Using System reference which should appear at the top of all C# files.