National Instruments 320685D-01 ユーザーズマニュアル

Chapter 4

Windows 3.1 Compiler/Linker Issues

LabWindows/CVI Programmer Reference Manual

4-4

©

 National Instruments Corporation

You must observe certain rules and restrictions in a DLL you want to use with 
LabWindows/CVI.   If you experience problems using a DLL in LabWindows/CVI, 
you might have to contact the developer of the DLL to obtain modifications.

Because LabWindows/CVI is a 32-bit application, special 

 is required to 

communicate with a 16-bit DLL. For some DLLs, LabWindows/CVI can automatically 
generate this glue code from the include file when loading the DLL. For other DLLs, you 
have to modify the glue source code and compile it with Watcom into a 

.obj

 or 

.lib

 file.

The normal way of communicating with a DLL is by calling functions in the DLL. However, 
cases exist where you must use other communication methods. The most typical case is that 
of an interrupt service routine in a DLL that notifies the application when an interrupt occurs. 
This is done through a callback function. Also, LabWindows/CVI can recognize messages 
posted by a DLL through the Windows Application Programming Interface (API) function 

PostMessage

 and initiate a callback function.

LabWindows/CVI provides two options that can be helpful when working with DLLs. The 
options can be found in the Run Options menu of the Project window:

•

Enable the Check Disk Dates Before Each Run option when you iteratively modify a 
DLL or DLL glue code file and run a LabWindows/CVI test program that calls into the 
DLL. By enabling the Check Disk Dates Before Each Run option, you ensure that you 
link the most recent version of the DLL and DLL glue code into your program. You can 
leave this option enabled at all times. The only penalty is a small delay each time you 
build or run the project. 

•

By default, LabWindows/CVI does not unload and reload DLLs between each execution 
of your program. This eliminates the delay in reloading the DLLs before each run. It 
allows the DLLs to retain state information between each run. If, however, you use a DLL 
that does not work correctly across multiple program executions, enable the Reload 
DLLs Before Each Run option. 

To call into a 16-bit DLL from LabWindows/CVI 32-bit code, you must observe the following 
rules and restrictions for DLL functions:

•

In the DLL header file, change all references to 

int

 into references to 

short

. 

•

In the DLL header file, change all references to 

unsigned

 or 

unsigned int

 to 

unsigned short

.

•

You can declare the functions in the DLL as 

PASCAL

 or as 

CDECL

.

•

You cannot use variable argument functions.

00ProRef.book : 06chap04.fm  Page 4  Monday, March 9, 1998  3:23 PM