KNOWNFOLDERID

KNOWNFOLDERID is a GUID-based identifier used by the Windows Shell to identify Known Folders in the user profile. It serves as a language- and profile-independent reference to standard folders, replacing older CSIDL identifiers in modern APIs. Each known folder has a corresponding GUID constant, such as FOLDERID_Desktop, FOLDERID_Documents, FOLDERID_Downloads, FOLDERID_Pictures, FOLDERID_Music, FOLDERID_Videos, FOLDERID_Templates, FOLDERID_PublicDocuments, and others. The IDs are defined in Windows header files (for example ShlObj.h and KnownFolders.h) and are exposed to applications as GUIDs.

Programs use these IDs with Known Folder APIs to obtain the path to a known folder. The key functions include SHGetKnownFolderPath, SHGetKnownFolderIDList, and the IKnownFolderManager interface. For example, SHGetKnownFolderPath(FOLDERID_Documents, 0, NULL, &path) returns the full path to the current user’s Documents folder, such as C:\Users\Name\Documents. The returned path reflects the runtime context and can adapt to per-user configurations and policy-driven locations.

Benefits of using KNOWNFOLDERID include localization neutrality, support for profile relocation, and consistency across user accounts and sessions. It also supports virtualized or redirected paths in modern Windows deployments. Some folders may be inaccessible due to permissions or policy, in which case the API returns a suitable error code (HRESULT).