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Q88278: Creating Import Libraries with the __export Modifier

Article: Q88278
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1
Operating System(s): 
Keyword(s): kb16bitonly
Last Modified: 29-AUG-2001

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) 3.1 
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SUMMARY
=======

The __export function modifier, widely advertised in version 7.0 of the
Microsoft C/C++ Optimizing Compiler, can be used in conjunction with the /GD
option switch to export a function from a dynamic-link library (DLL) for the
Microsoft Windows operating system without listing the name of the function in
the EXPORTS section of the DLL's module definition (.DEF) file.

To create an import library for a DLL that uses this technique, the filename of
the DLL must be listed as a parameter to the IMPLIB function. Otherwise, IMPLIB
does not place the functions marked with __export into the import library.

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

  __export and keyword and def and prolog

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

The first argument to the IMPLIB command is the name of the import library to
create. The second parameter is the name of the .DEF file, the name of the .DLL
file, or both. The syntax listed in the IMPLIB online help file is as follows:

  IMPLIB [options] implibname {dllfile... | deffile...}

If a .DEF file is listed as the second parameter, IMPLIB places all functions
listed in the EXPORTS section into the import library. This is the traditional
method of creating a DLL import library and it applies to versions of the
Microsoft C Compiler prior to version 7.0.

If a DLL file is listed as the second parameter, IMPLIB places all functions
marked with the __export keyword in the DLL source code in the import library.
This method is required when the DLL source code contains exported functions
that are not listed in the .DEF file. Otherwise, these functions would be
excluded from the import library.

In addition, if the DLL is developed in C++, the names of exported functions are
generally not available to place in the .DEF file because C++ decorates function
names. To create an import library for exported C++ functions, IMPLIB must read
the function names from the DLL.

To create an import library that contains only a subset of the functions marked
__export, create a .DEF file containing only the names of the functions to
include in the import library and specify the name of the .DEF file as an
argument to IMPLIB.

Note that any function that is marked with the __export keyword is compiled with
the default DLL export attributes in the import library. To modify any of the
attributes (for example, to add the NODATA or RESIDENTNAME attributes to the
exported function), you must list the function name in the EXPORTS section of a
.DEF file.

An example of a function that must be listed in the .DEF file is a WEP (Windows
exit procedure) function. Because the WEP must have the RESIDENTNAME attribute,
the following information must appear in the EXPORTS section of the DLL's .DEF
file:

     SEGMENTS 'WEP_TEXT' FIXED PRELOAD
     EXPORTS
        WEP  @1  RESIDENTNAME

The SEGMENTS declaration tells Windows to load the WEP_TEXT segment into a fixed
memory location as it loads the DLL into memory.

To place both the functions marked as __export and the WEP into the import
library, specify both the .DEF file and the .DLL file as arguments to the IMPLIB
command.

For more information on using Microsoft C/C++ 7.0 to create a WEP function
compatible with Windows 3.1, see pages 980 and 981 of the Microsoft Windows
Software Development Kit (SDK) "Programmer's Reference, Volume 2: Functions"
manual for version 3.1 and the DETAILS.TXT file distributed with Microsoft
C/C++.

For more information on using the /GD option switch with the __export keyword,
see page 515 of the Microsoft C/C++ "Environment and Tools" manual for version
7.0, or query in the Microsoft Knowledge Base on the word "/GD."

Additional query words: 3.10

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Keywords          : kb16bitonly 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1

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