INFO: LenB Function Returns in-Memory Size of User-Defined Type

MORE INFORMATION

Visual Basic 32-bit structures are DWORD aligned (four bytes) when stored in memory. Fixed-length strings use two bytes for every character to account for UNICODE. String descriptors use four bytes each. Integers use two bytes. Please refer to the Visual Basic Help file for the lengths of all the other data types.

Example One

Consider this example UDT:

     Type Generic
     FirstName as String * 5
     LastName as String
     ChildrenAges (1 to 5) as Byte
   End Type
				

This UDT requires the following number of bytes:

• FirstName uses 10 bytes (UNICODE).
• LastName uses 4 bytes (String descriptor).
• ChildrenAges uses 5 bytes (5-element byte array).

Applying DWORD alignment gives a total of 21 bytes as follows:

• 8 bytes for the first 8 bytes of FirstName.
• 8 bytes for the last 2 bytes of FirstName, 2 bytes of padding, 4 bytes for LastName.
• 5 bytes for the 5 bytes needed for ChildrenAges.

Therefore:

   LenB(Generic) = 21
   Len (Generic) = 14
				

Example Two

Consider this example UDT:

      Type Generic
     FirstName as String * 7
     LastName as String * 6
     ChildrenAges (1 to 5)  as Byte
     Address * String
   End Type
				

This UDT requires the following number of bytes:

• FirstName uses 14 bytes (UNICODE).
• LastName uses 12 bytes (UNICODE).
• ChildrenAges uses 5 bytes (5-element byte array).
• Address uses 4 bytes (string descriptor)

Applying DWORD alignment gives a total of 36 bytes as follows:

• 8 bytes for the first 8 bytes of FirstName.
• 8 bytes for the last 6 bytes of FirstName, 2 bytes of padding, 2 bytes for LastName.
• 8 bytes for the next 8 bytes of LastName.
• 8 bytes for the last 2 bytes of LastName, 5 bytes for ChildrenAges, and 1 byte of padding.
• 4 bytes for Address for the string descriptor.

Therefore:

   LenB(Generic) = 36
   Len (Generic) = 22