C# Signature:

[DllImport("ole32.dll")]
static extern int PropStgNameToFmtId([MarshalAs(UnmanagedType.LPWStr)]
   string oszName, out FMTID pfmtid);

VB.Net Signature:

<DllImport("ole32.dll", preservesig:=False)> _
Friend Shared Function PropStgNameToFmtId( _
    <MarshalAs(UnmanagedType.LPWStr)> ByVal oszName As String, _
    <Out()> ByRef FMTID As Guid) As Integer
End Function

User-Defined Types:

None.

Notes:

None.

Tips & Tricks:

To generate a FormatIdentifier from a custom PropertyStorage name use the following in VB.Net:

    Dim characters As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZ012345"

    Dim name As String = "MyPropertyStorageName
    Dim name As New StringBuilder(propertyStorageName)
    Dim bits As BitArray
    Dim i As Integer
    Dim j As Integer
    Dim index As Integer
    Dim idBytes() As Byte
    Dim idBits As BitArray

    idBits = New BitArray(130)    '26 * 5 - 26 Characters @ 5bits each      

    name = name.ToUpper    
    For i = 0 To name.Length - 1
        'Get the index of the current character and convert it to
        'a BitArray with a length of five (MaxValue = 31 hence the
        'character restriction
        index = characters.IndexOf(name.Chars(i))
        If index < 0 Then
           Throw New ApplicationException("Invalid Character")
        End If
        index = characters.IndexOf(Char.ToUpper(name.Chars(i)))
        bits = New BitArray(New Byte() _
        {CByte(index)})
        For j = 0 To 4
        idBits(j + (5 * i)) = bits(j)
        Next
    Next

    'A new Guid requires an array of exactly 16 bytes
    'Split the first 128 bits of the array into 8 bit chunks
    For i = 0 To 15
        ReDim Preserve idBytes(i)
        bits = New BitArray(8)
        For j = 0 To 7
        bits(j) = idBits(j + (8 * i))
        Next
        idBytes(i) = CByte(BitsToInteger(bits))
    Next
    Dim fmtId As New Guid(idBytes)

Guids generated with this will return the name using the FmtIdToPropStgName Function, and can be used to generate a new IPropertyStorage interface with IPropertySetStorage.Create(). The name returned will be filled to 26 chars with the letter 'a' due to the fixed size of a Guid and the fact that we're passing all zeros in the BitArray after the name finishes to reach this size.

Guids generated with this will return the name using the FmtIdToPropStgName Function. The name returned will be filled to 26 chars with the letter 'a' due to the fixed size of a Guid and the fact that we're passing all zeros in the BitArray after the name finishes to reach this size.

The following helper function is also required:

   Friend Function BitsToInteger(ByVal bits As BitArray) As Integer
    Dim int As Integer = 0
    Dim i As Integer
    For i = 0 To bits.Count - 1
        If bits(i) Then
        int += 2 ^ i
        End If
    Next
    Return int
    End Function

See Also: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/stg/stg/names_in_istorage.asp

Sample Code:

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