TIP #60: EXTERN MACRO CHANGE TO SUPPORT A WIDER SET OF ATTRIBUTES 
===================================================================
 Version:      $Revision: 1.21 $
 Author:       David Gravereaux <davygrvy_at_pobox.com>
               Donal K. Fellows <fellowsd_at_cs.man.ac.uk>
 State:        Rejected
 Type:         Project
 Tcl-Version:  8.6
 Vote:         Done
 Created:      Thursday, 06 September 2001
 URL:          https://tip.tcl-lang.org60.html
 Post-History: 

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 ABSTRACT 
==========

 This TIP proposes a change to how the EXTERN macro in /tcl.h/ works to 
 support a wider range of compiler specific attributes. 

 RATIONALE 
===========

 With working on Borland support recently, I found that luckily the 
 newest "free commandline tools" 
 [<URL:http://www.borland.com/bcppbuilder/freecompiler/>] does support 
 Microsoft's /__declspec(dllexport)/ attribute. But at the same time, 
 the older way with /__export/ is still valid, but can't be used due to 
 the order within the prototype declaration of the EXTERN macro. 

 What's this with the MS compiler: 

           __declspec(dllexport) __cdecl int func (int a, int b);

 will have to be this with Borland: 

           int __export __cdecl func (int a, int b);

 The order of the attribute needs to be after the return type. 

 Even though /__declspec/ is supported in the Microsoft style with 
 version 5.5+ of the Borland compiler, if EXTERN could swap around the 
 order a hair, old Turbo C v5.0 has a better chance to make a DOS 
 library. Should someone feel the need. 

 Let's leave the existing EXTERN macro as-is and just make a new one 
 called TCL_EXTERN to support the new behavior. 

 Karl Lembuaer (sp?) did a presentation @ OSCON regarding his recent 
 tinytcl project /%TODO: add link here%/ about his DOS port of Tcl 6.7 
 for use in a hand-held device. 

 Stepping backward for DOS support, may actually be a leap forward in an 
 off-beat manner... 

 REJECTED ALTERNATIVES 
=======================

 I saw something like this in a very old DDE extension that someone at 
 Sun wrote. It was used as an example windows extension for years. 

 <URL:ftp://tcl.activestate.com/pub/tcl/misc/example.zip> 

 In example.h is this: 

   #if defined(__WIN32__)
   #   if defined(_MSC_VER)
   #       define EXPORT(a,b) __declspec(dllexport) a b
   #   else
   #       if defined(__BORLANDC__)
   #           define EXPORT(a,b) a _export b
   #       else
   #           define EXPORT(a,b) a b
   #       endif
   #   endif
   #else
   #   define EXPORT(a,b) a b
   #endif
   
   EXTERN EXPORT(int,Example_Init) _ANSI_ARGS_((Tcl_Interp *interp));

 That work is doing the same job, but I prefer the method that I'm 
 proposing. 

 It is also mentioned on 
 <URL:http://tcl.activestate.com/doc/howto/winext.html> and feel it is 
 rather out-of-date and the order issue with /__export/ should be 
 brought into the core with this patch and be fix for good. 

 Is> 

           EXTERN int Foobar_Init (Tcl_Interp *interp);

 Proposed> 

           TCL_EXTERN(int) Foobar_Init (Tcl_Interp *interp);

 REFERENCE IMPLEMENTATION 
==========================

 
 <URL:https://sourceforge.net/tracker/download.php?group_id=10894&atid=310894&file_id=70480&aid=436116> 

 EXAMPLES 
==========

 Is: 

   EXTERN int
   Foobar_Init (Tcl_Interp *interp)
   {
   #ifdef USE_TCL_STUBS
       if (Tcl_InitStubs(interp, "8.1", 0) == NULL) {
           return TCL_ERROR;
       }
   #endif
       Tcl_CreateObjCommand(interp, "foobar", FooBar, NULL, NULL);
       return TCL_OK;
   };

 Proposed: 

   TCL_EXTERN(int)
   Foobar_Init (Tcl_Interp *interp)
   {
   #ifdef USE_TCL_STUBS
       if (Tcl_InitStubs(interp, "8.1", 0) == NULL) {
           return TCL_ERROR;
       }
   #endif
       Tcl_CreateObjCommand(interp, "foobar", FooBar, NULL, NULL);
       return TCL_OK;
   };

 Preprocessor output is the following: 

       Borland: 

   /* foobar.c 14: */extern  int __export
   /* foobar.c 15: */Foobar_Init (Tcl_Interp *interp)
   /* foobar.c 16: */{
   /* foobar.c 17: */
   /* foobar.c 18: */if (Tcl_InitStubs(interp, "8.1", 0) == 0) {
   /* foobar.c 19: */return 1;
   /* foobar.c 20: */}
   /* foobar.c 21: */
   /* foobar.c 22: */(tclStubsPtr->tcl_CreateObjCommand)(interp, "foobar", FooBar, 0, 0);
   /* foobar.c 23: */return 0;
   /* foobar.c 24: */};

       VC++: 

   extern  __declspec(dllexport) int
   Foobar_Init (Tcl_Interp *interp)
   {
   
       if (Tcl_InitStubs(interp, "8.1", 0) == ((void *)0)) {
           return 1;
       }
   #line 22 "foobar.c"
       (tclStubsPtr->tcl_CreateObjCommand)(interp, "foobar", FooBar, ((void *)0), ((void *)0));
       return 0;
   };

       MinGW (native gcc on win): 

   extern       int
   Foobar_Init (Tcl_Interp *interp)
   {
   
       if (Tcl_InitStubs(interp, "8.1", 0) == ((void *)0) ) {
           return 1 ;
       }
   
       (tclStubsPtr->tcl_CreateObjCommand) (interp, "foobar", FooBar, ((void *)0) , ((void *)0) );
       return 0 ;
   };

 RANDOM NOTES 
==============

 In /tclInt.h/ starting around line 1916, are prototypes for the 
 internal cmdprocs. I can't think of any reason why they should be 
 exported. Also note the comment about line:1673, as it states: 

   /*
    *----------------------------------------------------------------
    * Procedures shared among Tcl modules but not used by the outside
    * world:
    *----------------------------------------------------------------
    */

 As the current EXTERN macro places ""everything"" exportable, the use 
 of EXTERN following this comment in /tclInt.h/ is contradictory. In 
 place of EXTERN for this purpose I used the new TCL_EXTRNC in the 
 reference implementation. 

 COPYRIGHT 
===========

 This document has been placed in the public domain. 

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