Convert Code That Calls a DLL

See Also

Calling Procedures in the Windows Application Programming Interface

If a database created in previous versions of Microsoft Access called procedures in the Microsoft Windows application programming interface (API), you will need to make some changes in your code when you convert a version 2.0 or earlier database to Microsoft Access 2000.

The Windows API consists of a set of dynamic-link libraries (DLLs) containing system-related procedures that include functions, messages, data structures, data types, and statements you can use in creating applications that run under Windows 95 or the Windows NT platform. In order to call these procedures from Visual Basic, you must first declare them by using a Declare statement. You can then call them as you would any other procedure.

In versions 1.x and 2.0 of Microsoft Access were 16-bit applications and ran on 16-bit versions of Windows. Microsoft Access 2000 is a 32-bit application and runs only under Windows 95 and the Windows NT platform. If your existing Access Basic code made calls to a 16-bit Windows API, you will need to modify these calls when you convert your database to Microsoft Access 2000. The following list provides some tips for converting your code.

• Check any Declare statements to ensure that they refer to the correct DLLs. The following table shows the new names for the 32-bit Windows DLLs.

  16-bit Windows DLL	32-bit Windows DLL
  User.dll	User32.dll
  Kernel.dll	Kernel32.dll
  GDI.dll	GDI32.dll

  
  

• The names of some functions in the 32-bit Windows API have changed. Additionally, functions in the 32-bit Windows API are case-sensitive. Check to make sure that you've entered the procedure name and alias name correctly.
  
  
• Some functions have new parameter data types in the 32-bit Windows API. Consult one of the references listed later in this topic to determine which function calls you must update.
  
  
• If a16-bit version of a DLL with the same name as a 32-bit DLL exists on your computer, Microsoft Access may try to call a function in that DLL if the directory in which it resides precedes the directory that contains the new version in your path.
  
  
• Some 32-bit DLLs contain functions with slightly different versions to accommodate both Unicode and ANSI strings. An A at the end of the function name specifies the ANSI version. A W at the end of the function name specifies the Unicode version. If the function takes string-type arguments, try appending an A to the function name.

For more information on using 32-bit Windows API procedures and on porting your existing database applications to 32-bit Microsoft Access 2000, consult the following resources:

• The Windows API Viewer, available in the Microsoft Office 2000 Developer, includes Visual Basic syntax for all 32-bit declarations, data types, and constants.
  
  
• The Microsoft Office 2000 Resource Kit contains information on porting your 16-bit Microsoft Office-based solutions, including applications developed with previous versions of Microsoft Access, to 32-bit solutions.
  
  
• The Microsoft Win32 Software Development Kit provides complete reference information on 32-bit Windows API procedures.

Calling Code in Other DLLs

If your database application calls procedures in other DLLs, you must create or obtain 32-bit versions of those DLLs and make any necessary modifications to your code when you convert your database to Microsoft Access 2000.

If you can't obtain a 32-bit version of a DLL, then you'll need an intermediary DLL that can convert 32-bit calls to 16-bit calls. For more information, see the preceding resources list.