GetDiskFreeBytes – Determine number of free bytes on disk

Private Declare Function LoadLibrary Lib "kernel32" Alias "LoadLibraryA" (ByVal _    lpLibFileName As String) As LongPrivate Declare Function GetProcAddress Lib "kernel32" (ByVal hModule As Long, _    ByVal lpProcName As String) As LongPrivate Declare Function GetDiskFreeSpaceEx Lib "kernel32" Alias _    "GetDiskFreeSpaceExA" (ByVal lpDirectoryName As String, _    lpFreeBytesAvailableToCaller As Any, lpTotalNumberOfBytes As Any, _    lpTotalNumberOfFreeBytes As Any) As LongPrivate Declare Function GetDiskFreeSpace Lib "kernel32" Alias _    "GetDiskFreeSpaceA" (ByVal lpRootPathName As String, _    lpSectorsPerCluster As Long, lpBytesPerSector As Long, _    lpNumberOfFreeClusters As Long, lpTotalNumberOfClusters As Long) As Long' Return the number of free bytes available to caller, total bytes available ' to caller, and total free bytes on a disk. This function supports volumes' larger than 2G and Windows systems that supports disk quotas, where a' user might be prevented to use all the free space on disk.' If disk quotes aren't in use, the 1st and 3rd argument always return' the same values.' On entry, driveName is the name of a drive or a directory. If running on' Windows 95 OSR2 or later versions, you can also pass a UNC path, but in this' case you must append a backslash, as in "\MyServerMyShare". If you pass' a null string, the current drive is used.' On exit, the three arguments you've passed receive the desired information.' What makes this function advanced is that it is based on the' GetDiskFreeSpaceEx API function, which is available only on Windows 95' OSR2, Windows 98, Windows NT4 and later release. Before calling the API' routine, this function ensures that it is available, otherwise it' reverts to the older GetDiskFreeSpace API function.' Another detail that makes the implementation of this function more' difficult is that the GetDiskFreeSpaceEx routine expects pointers to' LARGE_INTEGER structures, which aren't supported in VB. The code below' uses Currency values, and then scales them up by 4 decimal positions.Sub GetDiskFreeBytes(driveName As String, FreeBytesAvailableToCaller As _    Currency, TotalBytesAvailableToCaller As Currency, _    TotalFreeBytes As Currency)    Dim hModule As Long, procAddr As Long, res As Long        ' first, determine whether we can call the GetDiskFreeSpaceEx function    hModule = LoadLibrary("kernel32.Dll")    If hModule Then        procAddr = GetProcAddress(hModule, "GetDiskFreeSpaceExA")        If procAddr Then            ' we call safely call the GetDiskFreeSpaceEx            ' Note that instead of passing LARGE_INTEGER values, we're            ' using Currency values (8 bytes)            res = GetDiskFreeSpaceEx(driveName, FreeBytesAvailableToCaller, _                TotalBytesAvailableToCaller, TotalFreeBytes)            ' decrement Dll's usage counter (not really necessary)            FreeLibrary hModule                        If res = 0 Then                ' a null result means error (probably invalid drive)                Err.Raise 5, , Err.LastDllError            Else                ' we must scale up the Currency by a factor of 10,000                FreeBytesAvailableToCaller = FreeBytesAvailableToCaller * 10000                TotalBytesAvailableToCaller = TotalBytesAvailableToCaller * _                    10000                TotalFreeBytes = TotalFreeBytes * 10000                Exit Sub            End If        End If        ' decrement Dll's usage counter (not really necessary)        FreeLibrary hModule    End If        ' if we get here, GetDiskFreeSpaceEx isn't available or raised an error    Dim lpSectorsPerCluster As Long    Dim lpBytesPerSector As Long    Dim lpNumberOfFreeClusters As Long    Dim lpTotalNumberOfClusters As Long        res = GetDiskFreeSpace(driveName, lpSectorsPerCluster, lpBytesPerSector, _        lpNumberOfFreeClusters, lpTotalNumberOfClusters)    If res = 0 Then        ' a null result means error (probably invalid drive)        Err.Raise 5, , Err.LastDllError    Else        ' return result through parameters        FreeBytesAvailableToCaller = lpNumberOfFreeClusters * _            lpSectorsPerCluster * lpBytesPerSector        TotalBytesAvailableToCaller = lpTotalNumberOfClusters * _            lpSectorsPerCluster * lpBytesPerSector        ' without quotas, this value is the same as FreeBytesAvailableToCaller        TotalFreeBytes = FreeBytesAvailableToCaller    End IfEnd Sub

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