HOWTO: Propagating Environment Variables to the System

ID: Q104011

The information in this article applies to:

Microsoft Win32 Software Development Kit (SDK) on the following platforms:
```
    - Microsoft Windows NT versions 3.5, 3.51, 4.0
```

SUMMARY

You can modify user environment variables by editing the following Registry key:

   HKEY_CURRENT_USER \ 
         Environment

You can modify system environment variables by editing the following Registry key:

   HKEY_LOCAL_MACHINE \ 
               SYSTEM \ 
    CurrentControlSet \ 
              Control \ 
      Session Manager \ 
          Environment

Note that any environment variable that needs to be expanded (for example, when you use %SYSTEM%) must be stored in the registry as a REG_EXPAND_SZ registry value. Any values of type REG_SZ will not be expanded when read from the registry.

Note that RegEdit.exe does not have a way to add REG_EXPAND_SZ. Use RegEdt32.exe when editing these values manually.

However, note that modifications to the environment variables do not result in immediate change. For example, if you start another Command Prompt after making the changes, the environment variables will reflect the previous (not the current) values. The changes do not take effect until you log off and then log back on.

To effect these changes without having to log off, broadcast a WM_SETTINGCHANGE message to all windows in the system, so that any interested applications (such as Program Manager, Task Manager, Control Panel, and so forth) can perform an update.

MORE INFORMATION

For example, on Windows NT, the following code fragment should propagate the changes to the environment variables used in the Command Prompt:

   SendMessageTimeout(HWND_BROADCAST, WM_SETTINGCHANGE, 0,
    (LPARAM) "Environment", SMTO_ABORTIFHUNG,
    5000, &dwReturnValue);

None of the applications that ship with Windows 95, including Program Manager and the shell, respond to this message. Thus, while this article can technically be implemented on Windows 95, there is no effect except to notify third-party applications. The only method of changing global environment variables on Windows 95 is to modify the autoexec.bat file and reboot.

Additional query words:

Keywords          : kbNTOS350 kbNTOS351 kbNTOS400 kbSysSettings kbGrpUser 
Issue type        : kbhowto

Last Reviewed: December 24, 1998