FILE_KNOWN_FOLDER_TYPE - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTIOAPI_H

typedef enum _FILE_KNOWN_FOLDER_TYPE
{
    KnownFolderNone,
    KnownFolderDesktop,
    KnownFolderDocuments,
    KnownFolderDownloads,
    KnownFolderMusic,
    KnownFolderPictures,
    KnownFolderVideos,
    KnownFolderOther,
    KnownFolderMax = 7
} FILE_KNOWN_FOLDER_TYPE;

#endif

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This enumeration is documented in Windows Driver Kit.