Environment Variables not Updating

[jgallen23]

For some reason the Environment.GetEnvironmentVariable("PATH") isn't reflecting the changes I've made in the control panel. If I restart, they return correctly. For example, if I add c:\testpath to my environment variables in window xp control panel, and then write a sample c# app to show the path (Console.WriteLine(Environment.GetEnvironmentVariable("PATH"));), the c:\testpath doesn't show up. anybody know how to fix this or if there is a way to update my environment variables?

[Ami Bar]

First processes environment variables are derived from its parent process. Second, once the environment variables are changed outside the application it will not effect running processes. If you change an environment variables while your application is running you won’t see it. If you change an environment variables while the parent process of your application is running you won’t see the change when your application runs. The later applies when you run your application in debug mode from the Visual Studio. If you run your application from the explorer (double click on it) it will get the correct environment variable. I know that when an environment variable is changed, Windows send a broadcast Windows’ message that it happened. Ami

[jgallen23]

Ami, Thanks, that makes a lot of sense. The problem I was having is that my application stays open the entire time and won't register the new path until it's restarted. Is there any way to programatically update the enviornment variables?

[Ami Bar]

If you have WinForm application you can override the WndProc method:

public class Form1 : Form
{
private const int WM_SETTINGCHANGE = 0x001A;

public Form1()
{
    InitializeComponent();
}

protected override void WndProc(ref Message m)
{
    // This is a message code that is sent when system-wide setting is changed
    if (WM\_SETTINGCHANGE == m.Msg)
    {
        if (m.LParam != IntPtr.Zero)
        {
            // Convert the LParam to string 
            string whatChanged = System.Runtime.InteropServices.Marshal.PtrToStringAuto(m.LParam);

            // Check if an Environment variable was changed 
            if (null != whatChanged && "Environment" == whatChanged)
            {
                // Here goes the code that updates your application
                MessageBox.Show("Environment variable changed");
            }
        }
    }
    // Don't forget to execute the message so the GUI will work.
    base.WndProc(ref m);
}

}

Ami