ID Number: Q71106
1.00
WINDOWS
Summary:
Calling some routines in dynamic link libraries (DLLs) requires BYTE
parameters in the argument list. Visual Basic possesses no BYTE data
type as defined in other languages such as C, which can create DLLs.
To pass a BYTE value correctly to an external FUNCTION (in a DLL),
which requires a BYTE data type, you must pass an integer data type
for the BYTE parameter.
This information applies to Microsoft Visual Basic Programming System
version 1.00 for Windows.
More Information:
Visual BASIC has the ability to call external code in the form of
dynamic link libraries (DLLs). Some of these libraries require BYTE
parameters in the argument list. An example of this is located in the
KEYBOARD.DRV FUNCTION as defined below:
FUNCTION GetTempFileName (BYTE cDrive,
LPSTR lpPrefix,
WORD wUnique,
LPSTR lpTempFileName)
GetTempFileName is documented on page 4-217 of the "Microsoft Windows
3.0 Software Development Kit, Reference - Volume 1." In Visual BASIC,
declare the FUNCTION on one line in the main module of your code:
DECLARE FUNCTION GetTempFileName LIB "keyboard.drv"
(BYVAL A%, BYVAL B$, BYVAL C%, BYVAL D$)
Because the architecture of the 80x86 stack is segmented into word
boundaries, the smallest type pushed onto the stack will be a word.
Therefore, both the BYTE and the integer will be pushed onto the stack
in the same manner, and require the same amount of memory. This is the
reason you can use an integer data type for a BYTE data type in these
types of procedure calls.
References:
1. "Programming Windows: the Microsoft Guide to Writing Applications
for Windows 3," by Charles Petzold (published by Microsoft Press,
1990)
2. "Microsoft Windows 3.0 Software Development Kit: Reference
Volume 1"
3. The WINSDK.HLP file shipped with Microsoft Windows 3.0 Software
Development Kit.