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Chapter 3

Windows 95/NT Compiler/Linker Issues

LabWindows/CVI Programmer Reference Manual

3-22

National Instruments Corporation

project. You must use the _

_stdcall

keyword in the declarations in the include file you

distribute with the DLL.

Other platforms, such as UNIX or Windows 3.1 do not recognize the

__stdcall

keyword.

If you work with source code that you might use on other platforms, you must use a macro in
place of

__stdcall

. The

cvidef.h

include file defines the

DLLSTDCALL

macro for this

purpose.

The following are examples of using the

DLLSTDCALL

macro.

int DLLSTDCALL MyIntFunc (void);

char * DLLSTDCALL MyStringFunc (void);

Note

You cannot use the __

stdcall

calling convention on functions with a variable

number of arguments. Consequently, you cannot use such functions in Microsoft
Visual Basic.

Exporting DLL Functions and Variables

When a program uses a DLL, it can access only the functions or variables that the DLL
exports. The DLL can export only globally declared functions and variables. The DLL cannot
export functions and variables you declare as

static

If you create your DLL in LabWindows/CVI, you can indicate which functions and variables
to export in two ways: the include file method and the qualifier method.

Include File Method

You can use include files to identify symbols to export. The include files must contain the
declarations of the symbols you want to export. The include files can contain nested

#include

statements, but the DLL does not export the declarations in the nested include

files. In the Create Dynamic Link Library dialog box, you select from a list of all the include
files in the project.

The include file method does not work with other compilers. However, it is similar to the

.def

method that the other compilers use.

Export Qualifier Method

You can mark each function and variable you want to export with an export qualifier.
Currently, not all compilers recognize the same export qualifier names. The most commonly
used qualifier is

__declspec(dllexport)

. Some also recognize

__export

LabWindows/CVI recognizes both. The

cvidef.h

include file defines the

DLLEXPORT

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