National Instruments 320685D-01 Compatibility with External Compilers

Chapter 3 Windows95/NT Compiler/Linker Issues

LabWindows/CVI Programmer Reference Manual 3-4

National Instruments Corporation

Note cvirte.dll contains the User Interface, Utility, Formatting and I/O, RS-232,

ANSI C, TCP, and DDE Libraries.

If you do not have a DLL import library or if the one you have contains references the DLL

does not export, you can generate an import library in LabWindows/CVI. You must have an

include file that contains the declarations of all the functions and global variables you want to

access from the DLL. The calling conventions of the function declarations in the include file

must match the calling convention of the functions in the DLL. For example, if the DLL

exports functions using the __stdcall calling convention, the function declarations in the

include file must contain the __stdcall keyword. Load the include file into a Source

window, and select the Generate DLL Import Library command in the Options menu.

Some fundamental differences exist in the way Windows95/NT and Windows 3.1 handle a

DLL that multiple processes use.

Windows95/NT creates a separate data space for each process that uses the DLL.

Windows3.1 creates only one data space for all processes that use the DLL.

Windows95/NT notifies a DLL each time a process loads or unloads it. Windows 3.1 does

not notify a DLL each time a process loads or unloads it. Windows 3.1 notifies the DLL only

when the first process loads it and the last process unloads it.

LabWindows/CVI for Windows95/NT unloads DLLs, by default, after each execution of a

user program in the development environment. This behavior more accurately simulates

what happens when you execute a standalone executable, and it is more suitable for

Windows95/NT DLLs that rely on load/unload notification on each execution of a program.

You can change the default behavior by turning off the Unload DLLs After Each Run option

in the Run Options dialog box of the Project window. National Instruments recommends,

however, that you leave the default behavior in effect.

Compatibility with External Compilers

LabWindows/CVI for Windows95/NT can be compatible at the object code level with

anyof the four compatible external compilers (Microsoft Visual C/C++, Borland C/C++,

WatcomC/C++, and Symantec C/C++). Because these compilers are not compatible with

each other at the object code level, LabWindows/CVI can be compatible with only one

external compiler at a time. This manual refers to the compiler with which your copy of

LabWindows/CVI is currently compatible as the current compatible compiler.