How to compile dll loadable in tcl

Question

After trying many and searching web option to compile and load dll I could not able to create dll for tcl. Can you explain me how to do this.

Answer 1

Ok, here is a simple example. This code compiles and works for Tcl8.5 and VS2008. To start with I created a WIN32 dll project called BasicTclExtn that exported symbols.

// BasicTclExtn.h
#ifdef BASICTCLEXTN_EXPORTS
#define BASICTCLEXTN_API __declspec(dllexport)
#else
#define BASICTCLEXTN_API __declspec(dllimport)
#endif

int BasicExtnCmd(ClientData data, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) ;
extern "C" {
    BASICTCLEXTN_API int Basictclextn_Init(Tcl_Interp *interp) ;
}

And then the .cpp file

// BasicTclExtn.cpp : Defines the exported functions for the DLL application.
#include "stdafx.h"
#include "BasicTclExtn.h"

int
BasicExtnCmd(ClientData data,
             Tcl_Interp *interp,
             int objc,
             Tcl_Obj *CONST objv[])
{

    // Check the number of arguments
    if (objc != 3) {
        Tcl_WrongNumArgs(interp, 1, objv, "arg arg");
        return TCL_ERROR;
    }

    long v1, v2, result ;

    if ( Tcl_GetLongFromObj(interp, objv[1], &v1) != TCL_OK)
        return TCL_ERROR ;

    if ( Tcl_GetLongFromObj(interp, objv[2], &v2)  != TCL_OK)
        return TCL_ERROR ;

    result = v1 + v2 ;

    Tcl_SetObjResult(interp, Tcl_NewIntObj(result)) ;
        return TCL_OK ;
}

    // Note the casing on the _Init function name
    BASICTCLEXTN_API int Basictclextn_Init(Tcl_Interp *interp)
    {
        // Link with the stubs library to make the extension as portable as possible
        if (Tcl_InitStubs(interp, "8.1", 0) == NULL) {
            return TCL_ERROR;
        }

        // Declare which package and version is provided by this C code
        if ( Tcl_PkgProvide(interp, "BasicTclExtn", "1.0") != TCL_OK ) {
            return TCL_ERROR ;
        }

        // Create a command
        Tcl_CreateObjCommand(interp, "BasicExtnCmd", BasicExtnCmd, (ClientData)NULL, (Tcl_CmdDeleteProc *)NULL);

        return TCL_OK ;
    }

You need to #include tcl.h in the stdafx.h.

This example uses the Tcl stubs facility, see the documentation on the Tcl_InitStubs function for more information; when using stubs you need to link to only the tclstub85.lib. To get the code to link properly you need to do the following:

• Add the include directory where tcl.h is installed to Configuration Properties -> C/C++ -> General -> Additional Include Directories
• Define the USE_TCL_STUBS symbol, I normally do this in Properties-> C/C++ -> Preprocessor -> Preprocessor Definitions. You may also find that you then need to define the <DLLNAME>_EXPORTS (BASICTCLEXTN_EXPORTS in my example) after this, I'm not sure why this happens.
• Add the path to the directory where the tclstub85.lib file is as an additional library directory in Configuration Properties -> Linker -> General -> Additional Library Directories.
• Add tclstub85.lib to Configuration Properties -> Linker -> Input -> Additional Dependancies
• If the compiler spits out a warning about MSVCRT then exclude MSVCRT by adding it to the ignored libraries in Configuration Properties -> Linker -> Input -> Ignore Specific Library.

All of these .lib, .dll and .h files should be easily found in your Tcl installation. You'll also need to ensure that the related tclstub85.dll and tcl85.dll can be found at run time, making sure the bin directory for Tcl is on the PATH should sort that out. So you should then be able to do the following from Tcl:

C:\Projects\BasicTclExtn\Debug>tclsh
% load BasicTclExtn.dll
% BasicExtnCmd 1 2
3
% BasicExtnCmd 1 2.p
expected integer but got "2.p"
% BasicExtnCmd 1 2
3
% BasicExtnCmd 1
wrong # args: should be "BasicExtnCmd arg arg"
% BasicExtnCmd 1 3
4
% exit

This is the simplest form of Tcl exstention, you can add additional calls to Tcl_CreateObjCommand() to add more commnds into this extension. Tcl provides some faciities to help with the processing of the command line paramters passed into the command. The example code used Tcl_WrongNumArgs() but you should also look at the Tcl_GetIndexFromObj() functions.

I would also suggest you get a copy of Practical Programming in Tcl and Tk by Brent Welch. You can read some sample chapter here http://www.beedub.com/book/, the chapter on C programming for Tcl from the 3rd edition will help you a lot.