PRB: Len and LenB May Differ on Size of User-Defined Types

• Standard, Professional, and Enterprise Editions of Microsoft Visual Basic, 32-bit only, for Windows, version 4.0

SYMPTOMS

When used with a user-defined type, the LenB function may return a different value than the Len function on 32-bit Windows platforms. This behavior occurs because the LenB function returns the in-memory size of a type, while the Len function returns the amount of size that a UDT would take if stored on disk. This occurs because Visual Basic 4.0 32-bit represents strings internally in Unicode, but externally (on disk) as ANSI. A string in the two-byte Unicode standard will occupy twice as much space as its ANSI equivalent.

STATUS

This behavior is by design.

MORE INFORMATION

The reproduction sample below demonstrates this behavior. Note that the fixed-length string is what causes different values for Len and LenB. The non-fixed-length string will always return a value of 4, because that is the space required to store a pointer to the location where the actual string is stored. The array of bytes of size five needs 5 bytes of storage, regardless of the contents of the array.

Steps to Reproduce

1. Start a new Visual Basic 4.0 32-bit project. Form1 is created by default.

2. Add a single module to the project by selecting Module from the Insert menu.

3. Add this code to the General Declarations section of Module1:

         Type MyUDT
            x As String * 5      'size of 10 or 5
            y As String       'size of 4
            z (1 to 5) As Byte   'size of 5
         End Type
   
   

4. Add this code to the Form_Click event of Form1:

         Private Sub Form_Click()
            Dim test As MyUDT
   
            test.x = "hello"
            test.y = "world"
            test.z(1) = 64
            test.z(2) = 65
            test.z(3) = 66
            test.z(4) = 67
   
            Print LenB(test)     'returns 21
            Print Len(test)      'returns 14
         End Sub
   
   

5. Press the F5 key or select Start from the Run menu to run the application and observe the behavior.

Keywords          : IAPVBA vb432 VB4WIN vbwin GnrlVb kbprg
Technology        : kbvba
Version           : WINDOWS:4.0
Platform          : NT WINDOWS
Issue type        : kbprb