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The __export keyword provided with the Visual C++ for Windows compiler is
obsolete with the Microsoft Visual C++ 32-bit compiler.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
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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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