National Instruments 320685D-01 Exporting DLL Functions and Variables, Include File Method, Export Qualifier Method

Chapter 3 Windows95/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 function s and v ariables
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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