Q107501: INFO: __declspec(dllexport) Replaces __export in 32-Bit VC++

Article: Q107501
Product(s): Microsoft C Compiler
Version(s): WINDOWS NT:1.0,2.0,4.0,5.0,6.0
Operating System(s): 
Keyword(s): kbLangC kbVC kbVC100 kbVC200 kbVC400 kbVC500 kbVC600
Last Modified: 10-MAY-2001

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The information in this article applies to:

- Microsoft Visual C++, versions 1.0, 2.0, 4.0 
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SUMMARY
=======

The __export keyword provided with the Visual C++ for Windows compiler is
obsolete with the Microsoft Visual C++ 32-bit compiler. The equivalent
functionality for WIN32 can be achieved by using the keyword __declspec with the
dllexport attribute. With Visual C++ 32-bit Edition, version 4.0, compiling code
containing the __export (or _export) keyword results in either of the following
warnings:

  C4236: nonstandard extension used : '__export' is an obsolete keyword, see
  documentation for __declspec(dllexport)

  - or -

  C4226: nonstandard extension used : '__export' is an obsolete keyword

Compiling code containing the __export (or _export) keyword with 32-bit Visual
C++, versions 1.0 and 2.x, results in the C4226 warning.


MORE INFORMATION
================

The __declspec construct is not supported by the tools supplied with Microsoft
Win32 Software Development Kit (SDK).

When porting DLL source code from Windows to Win32, replace each instance of
__export with __declspec( dllexport ). The __declspec(dllexport) keyword can be
used to export data, functions, classes, or class member functions. For
example:

     /* exported function */ 
     __declspec( dllexport ) void func();

     /* exported data */ 
     __declspec( dllexport ) int i;

     // exported class
     class __declspec( dllexport ) DLLClass
     {
        ...
     };

     class DLLClass
     {
     public:
         // exported member function
         __declspec( dllexport ) void MemberFunction( void );
     };

The sample code below demonstrates exporting classes and class member functions
from a DLL using the __declspec( dllexport ) and __declspec( dllimport ) storage
class attributes in the DLL and EXE, respectively.

Sample Code
-----------

     /* DLL Sample: TESTDLL.CPP
     /* Compile options needed: /D"_X86" /MT TESTDLL.CPP /link
     /*                  /DLL /OUT:testdll.dll /implib:testdll.lib
     */ 

     #include <stdio.h>

     class DLLClass
         {
         public:
          // exported member function
          __declspec( dllexport ) void functionA( void ) {
              printf("\nIn Function A of the exported function");
          }
         };

     // exported class
     class __declspec( dllexport) ExportDLLClass
         {
         public:
          void functionB(void) {
             printf("\nIn Function B of the exported class");
          }
         };

     // exported instance of the DLLClass
     __declspec(dllexport) DLLClass test;

     /* Source that calls the DLL Sample: CALLDLL.CPP
     /* Compile options needed: /D"_X86" /D"_CONSOLE" /ML CALLDLL.CPP
     /*                  TESTDLL.LIB
     */ 

     #include <stdio.h>

     class DLLClass
         {
         public:
          // imported member function
          __declspec( dllimport ) void functionA( void );
         };

     class __declspec( dllimport) ExportDLLClass
         {
         public:
          void functionB(void);
         };

     __declspec( dllimport ) DLLClass test;

     void main(void)
     {
        ExportDLLClass TestClass;

        test.functionA();
        TestClass.functionB();
     }

REFERENCES
==========

For more information on exporting, query on the following words in the Microsoft
Knowledge Base:

  __export and def and prolog and dllexport


For more information creating DLLs for WIN32 or on the dllexport and dllimport
storage class attributes, refer to Chapter 4 of the "Programming Techniques"
manual that ships with Visual C++ 32-bit Edition, or search for dllexport or
dllimport or export in the Visual C++ Books Online. >From within the Visual
Workbench, select Help and choose Keyword Search.

Additional query words: 8.00 9.00

======================================================================
Keywords          : kbLangC kbVC kbVC100 kbVC200 kbVC400 kbVC500 kbVC600 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbvc100 kbVC500 kbVC600 kbVC200 kbVC32bitSearch kbVC500Search
Version           : WINDOWS NT:1.0,2.0,4.0,5.0,6.0

=============================================================================

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