Using the Registry Properly

[This is preliminary documentation and subject to change.]

• Do not store hard-coded path names in the registry. Use system environment variables wherever possible. This allows administrators to redirect components and remap drive letters. Important environment variables are:

  %UserProfile%\

  %Temp%\

  %ProgramFiles%\

  %SystemDrive%\

  %SystemRoot%\

  This is also a Designed for Windows Logo recommendation.

• Register classes on a per-user basis. On Microsoft® Windows NT® 5.0, be sure to register class information in HKEY_CURRENT_USER (in HKCU\Software\Classes).
• Use the correct access mask when opening a registry key. Use KEY_READ and KEY_WRITE rather than KEY_ALL_ACCESS.
• Store user settings separately from computer settings. User settings and computer settings are different. Computer settings do not vary from user to user. As a general rule, user settings should be recoverable, and computer settings reconstructable.

  Do not store a mixture of user information and computer information together, and definitely do not store them with the application binaries, where they will be lost if the computer fails.

  This is also a Designed for Microsoft Windows Logo requirement.

• Store small user setting data in HKEY_CURRENT_USER (HKCU).
• Store large user-profile data in the Application Data folder. Store any user-profile information that is too large to be suitable for the registry in the Application Data folder of the user's Profile. Get the path to this folder by calling SHGetSpecialFolderLocation with CSIDL_APPDATA.

  For more information, see the applicable Designed for Windows Logo recommendation.

• Store hardware-independent computer settings in HKLM. Installed hardware can change, whether by docking and undocking, computer replacement, presence or absence of portable peripherals, and so forth. HKEY_LOCAL_MACHINE should contain static information that has to do with the logical computer in the context of the enterprise, as opposed to an actual physical configuration of that computer.
• Store hardware-dependent computer settings in HKCC. HKEY_CURRENT_CONFIG is the place to store all hardware-related data about the computer's configuration.
• Do not assume that HKEY_CURRENT_USER is initialized. In a multi-user environment an application can be installed on a computer without setup having had an opportunity to initialize HKEY_CURRENT_USER (HKCU) for the user who starts the application. Supply a reasonable default value for each user setting, and use it if the corresponding registry key is not present in HKCU. This is also a logo recommendation.