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How to: Query for the Total Number of Bytes in a Set of Folders (LINQ) (Visual Basic)

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This example shows how to retrieve the total number of bytes used by all the files in a specified folder and all its subfolders.

Example

The Sum method adds the values of all the items selected in the select clause. You can easily modify this query to retrieve the biggest or smallest file in the specified directory tree by calling the Min or Max method instead of Sum.

Module QueryTotalBytes  
    Sub Main()  
  
        ' Change the drive\path if necessary.  
        Dim root As String = "C:\Program Files\Microsoft Visual Studio 9.0\VB"  
  
        'Take a snapshot of the folder contents.  
        ' This method assumes that the application has discovery permissions  
        ' for all folders under the specified path.  
        Dim fileList = My.Computer.FileSystem.GetFiles _  
                  (root, FileIO.SearchOption.SearchAllSubDirectories, "*.*")  
  
        Dim fileQuery = From file In fileList _  
                        Select GetFileLength(file)  
  
        ' Force execution and cache the results to avoid multiple trips to the file system.  
        Dim fileLengths = fileQuery.ToArray()  
  
        ' Find the largest file  
        Dim maxSize = Aggregate aFile In fileLengths Into Max()  
  
        ' Find the total number of bytes  
        Dim totalBytes = Aggregate aFile In fileLengths Into Sum()  
  
        Console.WriteLine("The largest file is " & maxSize & " bytes")  
        Console.WriteLine("There are " & totalBytes & " total bytes in " & _  
                          fileList.Count & " files under " & root)  
  
        ' Keep the console window open in debug mode  
        Console.WriteLine("Press any key to exit.")  
        Console.ReadKey()  
    End Sub  
  
    ' This method is used to catch the possible exception  
    ' that can be raised when accessing the FileInfo.Length property.  
    Function GetFileLength(ByVal filename As String) As Long  
        Dim retval As Long  
        Try  
            Dim fi As New System.IO.FileInfo(filename)  
            retval = fi.Length  
        Catch ex As System.IO.FileNotFoundException  
            ' If a file is no longer present,  
            ' just return zero bytes.
            retval = 0  
        End Try  
  
        Return retval  
    End Function  
End Module

If you only have to count the number of bytes in a specified directory tree, you can do this more efficiently without creating a LINQ query, which incurs the overhead of creating the list collection as a data source. The usefulness of the LINQ approach increases as the query becomes more complex, or when you have to run multiple queries against the same data source.

The query calls out to a separate method to obtain the file length. It does this in order to consume the possible exception that will be raised if the file was deleted on another thread after the FileInfo object was created in the call to GetFiles. Even though the FileInfo object has already been created, the exception can occur because a FileInfo object will try to refresh its Length property with the most current length the first time the property is accessed. By putting this operation in a try-catch block outside the query, the code follows the rule of avoiding operations in queries that can cause side-effects. In general, great care must be taken when you consume exceptions to make sure that an application is not left in an unknown state.

Compile the code

Create a Visual Basic console application project, with an Imports statement for the System.Linq namespace.

See also