PRB: Exceeded Limits on Array Sizes of User Defined Types

• Standard, Professional, and Enterprise Editions of Microsoft Visual Basic, 16-bit and 32-bit, for Windows, version 4.0

SYMPTOMS

When compiling code that has user-defined types containing arrays of variable-length strings you may get this error:

   "Fixed or static data can't be larger than 64K"

CAUSE

You exceeded the data limitations of a user-defined type. As stated in the Programmer's Guide for Microsoft Visual Basic version 4.0:

   No variable of a user-defined type can exceed 64K, though the sum of
   variable-length strings in a user-defined type may exceed 64K
   (variable-length strings occupy only 4 bytes in the user-defined type;
   the actual contents of a string are stored separately. User-defined
   types can be defined in terms of other user-defined types, but the total
   aggregate size of the types cannot exceed 64K.

RESOLUTION

Consider the following example code:

Type MyData1

   sdata(80) As String

Type MyData2

   uset(300) as MyData1

The amount of storage required is 80*4*300 or 96000 bytes, which exceeds the 64K limit.

In Visual Basic version 4.0, the pointers to the string data are far pointers that use both the segment and offset addresses, so the pointers to the string data and the string data itself do not compete for space in the same 64K data segment.

Therefore, because the string content is stored separately and the string data can be stored in a different data segment from the pointers, you can store large amounts of data in arrays of variable-length strings in user-defined types. However, because the pointers to the string data are far and each requires four bytes in the user-defined type, you must design your data storage scheme to store more data in fewer elements.

In the above example, you need to decrease the dimension of uset(300) to approximately uset(200), and store more data in the elements of sdata in order to take advantage of how strings are stored internally.

In most cases, you can create an object with the data storage you require. The exception is if you require a user-defined type to map an external data structure in a DLL. In this case, you need to design your data storage scheme such that you store a large amount of data in fewer elements in arrays of variable-length strings.

STATUS

This behavior is by design.