National Instruments 320685D-01 DLLs for Instrument Drivers and User Libraries, Using The LoadExternalModule Function , Link Errors when Using DLL Import Libraries, DLL Path (.pth) Files Not Supported, 16-Bit DLLs Not Supported, Run State Change Callbacks in DLLs

Chapter 3 Windows95/NT Compiler/Linker Issues

LabWindows/CVI Programmer Reference Manual 3-2

National Instruments Corporation

DLLs for Instrument Drivers and User Libraries

Under Windows 95/NT, LabWindo ws/CVI does not directly associate DLLs with instrument

drivers or user libraries. However, LabWindows/CVI can associate instrument drivers and

user libraries with DLL import libraries. Each DLL must have a DLL import library (.lib)

file. In general, if the program for an instrument driver or user library is in the form of a DLL,

you must place the DLL import library in the same directory as the function panel (.fp) file.

The DLL import library specifies the name of the DLL that LabWindows/CVI searches for

using the standard Windows DLL search algorithm.

LabWindows/CVI makes an exception to facilitate using VXIplug&play instrument driver

DLLs. When you install a VXIplug&play instrument driver, the installation program

does not place the DLL import library in the same directory as the .fp file. If a .fp file

is in the VXIplug&play directory, LabWindows/CVI searches for an import library in

the VXIplug&play library directory before it looks for a program file in the directory of

the .fp file, unless you list the program file in the project.

Using The LoadExternalModule Function

When you use the LoadExternalModule function to load a DLL at run time, you must

specify the pathname of the DLL import library, not the name of the DLL.

Link Errors when Using DLL Import Libraries

A DLL import library must not contain any references to symbols that the DLL does not

export. If it does, LabWindows/CVI reports a link error. If you load the DLL using

LoadExternalModule, the GetExternalModuleAddr function reports an undefined

references (–5) error. You can solve this problem by using LabWindows/CVI to generate an

import library. Refer to the Generating an Import Library discussion later in this section.

DLL Path (.pth) Files Not Supported

The DLL import library contains the filename of the DLL. LabWindows/CVI uses the

standard Windows DLL search algorithm to find the DLL. Thus, DLL path (.pth)

files do not work under Windows95/NT.

16-Bit DLLs Not Supported

LabWindows/CVI for Windows95/NT does not load 1 6-bit DLLs. If you want to do this, you

must obtain a 32-to-16-bit thunking DLL and a 32-bit DLL import library.

Run State Change Callbacks in DLLs

You can include run state change callbacks in DLLs you build in LabWindows/CVI. When

running a program in LabWindows/CVI, a run state change callback receives notification

when the program starts, suspends, resumes, and stops. If you include a run state change