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GetCompressedFileSize (kernel32)

C# Signature:

static extern uint GetCompressedFileSize(string lpFileName,
   out uint lpFileSizeHigh);

VB .NET Signature:

Private Declare Function GetCompressedFileSize Lib "kernel32" Alias "GetCompressedFileSizeA" (ByVal lpFileName As String, ByVal lpFileSizeHigh As IntPtr) As UInt32

Legacy VB Signature:

Private Declare Function GetCompressedFileSize Lib "kernel32" Alias "GetCompressedFileSizeA" (ByVal lpFileName As String, lpFileSizeHigh As Long) As Long

User-Defined Types:



The code below correctly obtains the compressed file size also if above 4GB. (Fixed VB and C# code, 2012 Eske Rahn)

Tips & Tricks:

Please add some!

Sample Code C#:

    [DllImport("kernel32.dll", SetLastError=true, EntryPoint="GetCompressedFileSize")]
    static extern uint GetCompressedFileSizeAPI(string lpFileName, out uint lpFileSizeHigh);

    public ulong GetCompressedFileSize(string filename)
        uint high;
        uint low;
        low = GetCompressedFileSizeAPI(filename, out high);
        int error = Marshal.GetLastWin32Error();
        if (low == 0xFFFFFFFF && error != 0)
        throw new Win32Exception(error);
        return ((ulong)high << 32) + low;

Sample Code VB .NET:

Imports System.IO
Public Function CompressedFileSize(ByVal path As String) As Long
   If File.Exist(path) Then
       ' Return Convert.ToInt64(GetCompressedFileSize(path, IntPtr.Zero))

       ' To handle 4Gb+ a bit more complex:
       Dim ptr As IntPtr = Marshal.AllocHGlobal(4)
         Dim filelength as Long = Convert.ToInt64(GetCompressedFileSize(path, ptr))
         If filelength = &HFFFFFFFF Then
           Dim Err As Long = Marshal.GetLastWin32Error()
           If Err <> 0 Then Throw New IOException("Exception getting compressed size: " & Err.ToString)
         End If
         Return filelength + CLng(Marshal.ReadInt32(ptr)) << 32
       End Try
     Catch ex As Exception
       Throw New IOException("The compressed size of the specified file could not be determined.")
     End Try

   End If

End Function

Sample code legacy VB:

Private Sub GetFileSize(ByVal strPath As String)
   MsgBox "The size of " + strPath " is " + CStr(GetCompressedFileSize(strPath, ByVal 0&)) + " bytes "
End Sub

Alternative Managed API:

The ManagedWindowsApi project ( provides an ExtendedFileInfo class that contains utility methods for file information.


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