'''Extending Tcl''' is a [Tcl Extension: Developer Guide%|%guide%|%] to writing [Tcl] [extension%|%extensions]. ** See Also ** [Extending Tcl in C from Tcl], by [RS]: Provides `cextend`, which takes some C code and generates a Tcl interpreter that exposes it as a Tcl command. [Extension Developer's Wishlist for Tcl]: [Extension Stubs Tables]: using your tcl extension1 (at [C] level). [How to debug memory faults in Tcl and extensions]: [Stubs]: [Tcl extension prototype - proto.cpp]: [What 'extension' means]: [Writing extensions for stubs and pre-stubs Tcl]: [extension]: [RPC]: An alternative to extending Tcl is to offload functions to another process. [Tips for writing quality software]: [Useful C Commands For Tcl]: [Creating Extensions in C++]: [Tcl C API]: The [C] functions that [Tcl] makes available [http://www.cs.man.ac.uk/~fellowsd/tcl/scidx.html%|%Donal K. Fellows's Small C Extensions]: Most, if not all of what is here that is useful has by now migrated into Tcl itself. ** Further Reading ** [BOOK Practical Programming in Tcl and Tk, Third edition]: Chapter 44 on the Tcl C API is available [http://www.beedub.com/book/3rd/bookTOC.html%|%online]. [http://phaseit.net/claird/comp.lang.tcl/HowToC.html%|%Cameron Laird's personal notes on how to use C with Tcl]: Circa 2000 ** Tutorials ** [TEA] documentation: [http://www.equi4.com/jcw/extuse.html%|%How to use extensions in Tcl%|%]: by [JCW%|%Jean-Claude Wippler], 1998-05. A fine "how-to" for those who find themselves needing to build extensions that other people have written. [Book Practical Programming in Tcl and Tk%|%Practical Programming in Tcl and Tk]: by Brent Welch. The chapters "C Programming and Tcl" and "Compiling Tcl and Extensions." (available online) are relevant. ** Dated Tutorials ** [Writing a Tcl extension : the Toocl example, Cédric BEUST 1995]: predates `Tcl_Obj` API's HTML version of the ''TclCommandWriting'' man page that comes with [TclX]: Explains the This page explains the C API to Tcl, providing an introduction/tutorial on writing Tcl extensions. This paper, too, predates the ''Tcl_Obj'' API's. ** Code Generation Tools ** [C code generators], by [RS]: A few tools for embedding [C] code into a Tcl script. [Critcl]: [JCW]: Another way to get an extension off the ground in no time. Described in [http://www.digital-smarties.com/Tcl2002/critcl.pdf] [C Code Generators]: part of [RS]'s three-part 'Xmas2000' project, presents some Tcl scripts that automatically generate the repetitive C code that extensions use to get themselves connected with the Tcl interpreter. He didn't manage to build a [load]able DLL on his slightly ancient gcc though... [SWIG]: Generates wrappers for [C], [C++], and [Objective-C] functions in various scripting languages, including Tcl. [tcltcc]: A Tcl extension wrapping [tcc]. Partially emulates the Critcl API. [Mktclapp]: A Tool For Mixing C/C++ with Tcl/Tk. [Tcl++]: A package that makes development of extended Tcl/Tk interpreters easier and more pleasant for C++ programmers. [tclbind] (historical?): Dode to perform bindings of Tcl commands to C++ member functions. Requires [TclX], but can also support TCL-DP. [tclobj]: Access C++ classes and to operate C++ objects. [cpptcl]: several tools for working with [C++] [xWizard]: A C/C++ program can be easily wrapped into a Tcl extension. [Object Tcl] (historical?): Provides tight object-oriented coupling to C++ [jWrap]: circa 1999 library that parses [C]/[C++] headers or source in order to automatically produce a C/C++ glue stub that can be linked with your component library to produce a loadable Tcl [extension]. [TclObjectCommand] (historical?): Define Tcl commands which manipulate C++ class and structure objects in manners similar to the way Tk manages widgets. [Itcl++] (historical?): Parses C++ header files and generates a one-to-one mapping of C++ classes to itcl classes. [tcl_object] (historical?): C++ code which allows you to develop a bi-directional interface to Tcl. [Hush] (historical?): A [C++] API for Tcl [Joy] (historical): Integration between various langugages. ** System Libraries ** [COM]: [TWAPI COM support%|%TWAPI], [tcom], [optcl] are some available interfaces [Microsoft Windows API]: [TWAPI] is the primary Tcl interface [POSIX]: [TclX] provides access to various system facilities ** General Interfaces ** [Ffidl%|%ffidl%|%]: If your only purpose for developing an extension is to provide an interface to some third-party library, you may be able to avoid writing any C or C++ code altogether. Ffidl provides a nearly universal means of invoking shared libraries from Tcl on a number of platforms. ** Example Extensions ** [SampleExtension]: the "official" example of a Tcl [C] extension [extension example]: the most basic sample extension [Hello World as a C extension]: provides a bare-bones sample extension in C with details of how to actually set up your environment and build an actual extension, and then how to load it into Tcl to try it out. [http://core.tcl.tk/tcl/dir?ci=388ef7d2c16b81da&name=unix/dltest%|%unix/dltest] in the source distribution: files for testing Tcl's dynamic loading/unloading capabilities [RPN C extension for Tcl]: [C++ object-style Tcl example extension], by [Jos Decoster]: A clean, modern example of a C++ extension [http://www.omanurkka.fi/files/test.c.txt%|%Minimal Tcl Extension Example%|%]: [useless tcl extension]: [http://www.iki.fi/mjk/files/test.c.txt%|%A Minimal Tcl Extension Example]: Missing the [stubs] verbiage. ** Design ** [Concepts of Architectural Design for Tcl Applications]: ** Coding Techniques ** [How do I use the Tcl C API?]: [http://www.tcl.tk/doc/engManual.pdf%|%Tcl/Tk Engineering Manual%|%]: the engineering guide for the Tcl core implementation and C-level extension [Managing the reference count of Tcl objects]: A summary of when to use ''Tcl_IncrRefCount'' and ''Tcl_DuplicateObj'' [Using Tcl_ListObj and his friends]: [Blessed Tcl_Obj values]: [Tcl Handles]: Presents in detail two methods for representing pointers to the Tcl program. The first represents program objects with Tcl command names; the second uses opaque "handles". These are the two fundamental ways to pass around C/C++ structures in Tcl scripts. [HOWTO: Make a Tcl Extension Thread-Safe]: [Thread-safe Tcl Extensions]: [Invoking Tcl commands from Cplusplus]: A C++ class that allows fast callbacks from C++ to tcl commands. [Cplusplus streams and Tcl channels]: A C++ iostream class that connects to a Tcl I/O channel. Includes initialization code to remap ''cin'', ''cout'' and ''cerr'' to the Tcl channels ''stdin'', ''stdout'', and ''stderr'' so that C++ I/O happens on the Tcl console. [Tclobj%|%Making C++ Loadable Modules Work%|%]: Part of the [Tclobj] documentation, by Frank Pilhofer, gives an overview of the various platform-dependent tricks needed to make C++ extensions work in the various Unix environments. ** Windows ** For information at building Tcl extension using Cygnus's Cygwin environment, take a look at the following files: [http://www.flightlab.com/%7Ejoe/tcl/cygwin-howto.txt%|%HOWTO: Using CYGWIN to build a Tcl extension on Windows%|%]: by [Joe English] [http://www.tcl.tk/doc/tea/windows.html%|%TEA on Windows%|%]: but see also [Annotated 10 steps to success with TEA] for a contrarian view. [http://www.xraylith.wisc.edu/%7Ekhan/software/gnu-win32/%|%GNU Win32 related projects%|%]: by Mumit Khan [http://sourceware.cygnus.com/cygwin/faq/faq_toc.html%|%The Cygwin FAQ]: ** Description ** Reasons for extending Tcl include exposing an external [API], and increasing the speed of a CPU-intensive calculation. Probably the easiest way to call C from Tcl is via [CriTcl]. CriTcl allows you to embed C functions within a Tcl script, compiling and cached the results the first time they are invoked. From then on the compiled C code will be dynamically loaded. You can also use CritBind to pre-build libraries or executables. [stevel]: See [CriTcl builds C extensions on-the-fly] for more information. ---- '''Note that''' `interp->result` is now [Tcl_GetStringResult() forward compatibility%|%forbidden%|%]. ---- (putatively) [DKF]: If you want to learn how to write a Tcl command in C, one of the easiest places to look is the Tcl sources themselves. Particularly, try looking in .../generic/tclCmd??.c. For example, look at the definition of the `[source]` in the function `Tcl_SourceObjCmd`, in `tclCmdMZ.c`. If there's a simpler command than that in the sources, I don't know of it. An example: ======c #include int Md5CryptCmd(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) { Tcl_Obj *saltObj, *passwordObj; char tmpBuffer[TMP_BUF_SIZE]; /* Or whatever! */ if (objc != 3) { Tcl_WrongNumArgs(interp, 1, objv, "salt password"); return TCL_ERROR; } saltObj = objv[1]; passwordObj = objv[2]; yourFunctionToDoTheRealWork(Tcl_GetString(saltObj), Tcl_GetString(passwordObj), &tmpBuffer); Tcl_SetResult(interp, tmpBuffer, TCL_VOLATILE); return TCL_OK; } ====== OTOH, using `Tcl_GetIntFromObj()` is a little more complex because that can fail (e.g. when the argument is something like "foobar" ) ======c int FoobarCmd(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) { int foo, bar, resultValue; if (objc != 3) { Tcl_WrongNumArgs(interp, 1, objv, "foo bar"); return TCL_ERROR; } if (Tcl_GetIntFromObj(interp, objv[1], &foo) != TCL_OK || Tcl_GetIntFromObj(interp, objv[2], &bar) != TCL_OK) { /* There's already a nice error message */ return TCL_ERROR; } resultValue = yourFunctionToDoTheRealWork(foo, bar); /* There's other ways to do this, but they're not much more efficient and are definitely less clear */ Tcl_SetObjResult(interp, Tcl_NewIntObj(resultValue)); return TCL_OK; } ====== ** Overview of the methods ** With executable modules (EM), exposure of the Tcl C [API] is not needed. Building an executable module is generally easier than writing a C extension for Tcl. The Tcl [exec] command can be used to start a module and send it initial data. For most EM however the [open] command is more useful, because you can use it to create a two-way pipeline. Debugging is easier with an EM, because Tcl isn't involved in the function of the module. It's also reasonable to assume that an EM works with most scripting languages, and is thus not dependent on Tcl. The Tcl C [API] is powerful and for something like a new data type for a tree, threads, or other things that can not be easily done with executable modules it's a good solution. [Critcl] is a newcomer to the world of Tcl. It compiles an extension on the fly based on C code embedded in a Tcl script. It can't be used for all extension work, but for many things it's good. [[todo findout more about how well it works]] A variation on the methods employed by [Critcl] allows [Fortran] programmers to write extensions for Tcl - it is called Critclf (not very imaginative :), I admit) and is currently under development. Contact [AM] for more information. [Mktclapp] has an [API] for writing extensions. It can be used to generate a stand-alone application by generating C code, or a load'able shared object library. It can also be used to convert a Tcl script or scripts into C code for compilation with a C compiler, so its use is beyond just extensions. [SWIG] automates the task of generating an extension. It can generate an interface for Tcl and other languages, which can then be compiled. [[How well does it work? What is it good at doing?] [xWizard] can generate template C/C++ code for Tcl extension. It is a GUI program written by pure Tcl/Tk so it works for cross-platform. More details in http://www.neatware.com/myrmecox/professional/wizard.html ** Executable Modules (EM) ** An EM is one of the easiest methods for extending Tcl. It's possible to build an EM from other Tcl scripts, Perl scripts [[but why would anyone want to do that?]], or some other language [[surely this third option is the most common?]], but sometimes a program usable as an EM already exists and then one doesn't even have to create it. An EM typically communicates with a Tcl pipe created with [open]. Tcl supports binary data over two-way pipes, via [fconfigure] and -translation binary, so theoretically any data can be transferred. It's also possible to use shared memory. '''Pro:''' 1. Any language may be used for an EM. 2. Debugging may be easier, because programs have an extra memory boundary. 3. Testing may be easier, because the program can be tested alone (interactively in many cases). '''Con:''' 1. Performance may be an issue if lots of I/O is required. 2. Shared state can be a problem. A possible solution is shared memory. 3. Complex/structured data can be a problem. Tcl handles serializing very well, but other languages are often weak in this area. ======c /* * By George Peter Staplin * This is version 2 of a simple executable-module written in C. * This is simply a demonstration. */ #include #include #include #include #include #define SEPFMT " \t\n" void get_input (char *buf, size_t s) { if (NULL == fgets (buf, s, stdin)) { if (feof (stdin)) { exit (EXIT_SUCCESS); } exit (EXIT_FAILURE); } } int expect_int (void) { char *t = strtok (NULL, SEPFMT); char *end; long l; if (NULL == t) { fprintf (stderr, "premature end of token stream.\n"); exit (EXIT_FAILURE); } l = strtol (t, &end, 10); if ((LONG_MIN == l && ERANGE == errno) || (end < (t + (strlen (t) - 1)))) { fprintf (stderr, "invalid integer '%s'\n", t); exit (EXIT_FAILURE); } return (int) l; } int main (int argc, char *argv[]) { char buf[1024]; char *tok; again: get_input (buf, sizeof (buf)); tok = strtok (buf, SEPFMT); if (NULL == tok || 1 != strlen (tok)) { fprintf (stderr, "invalid operator: '%s'\n", tok); exit (EXIT_FAILURE); } switch (tok[0]) { case '+': printf ("%d\n", expect_int () + expect_int ()); break; case '-': { int a, b; a = expect_int (); b = expect_int (); printf ("%d\n", a - b); } break; default: fprintf (stderr, "unknown operator: '%c'\n", tok[0]); exit (EXIT_FAILURE); } goto again; return EXIT_FAILURE; } ====== To use the code above as a module we will use a two-way pipe. Tcl uses the | character in the [open] command to create a pipe. We will [open] the pipe for '''w+''' also known as read-and-write mode. The [gets] command is used to retrieve the result. The read command could also be used, although it would require a fixed-length format, non-blocking I/O, or a read of a single character until \n is reached. ====== #!/bin/tclsh8.4 set ::mathModule [open {|./modmath} w+] proc modMath {args} { puts -nonewline "$args is " puts $::mathModule $args flush $::mathModule return [gets $::mathModule] } proc main {} { puts [modMath + 200 300] puts [modMath - 5600 1243] puts Done } main ====== ** Tcl C API ** The Tcl C API is quite powerful. There are at least 2 approaches to extending Tcl via the C API. A new tclsh-like shell can be created, or a loadable extension can be [load]ed into an interpreter. Our first example will be a new interactive shell that performs simple addition. This will teach you how to create a Tcl interpreter, initialize Tcl, and create a simple command for addition. '''Pro:''' 1. The C API is powerful and some things can be done that are impossible to do with an EM. 2. The C API can be used as a portable abstract layer for I/O, and other uses. 3. Performance is generally excellent -- provided that you choose the right algorithms. '''Con:''' 1. [Tcl_Obj] management can be tricky for beginners. Bad Tcl_Obj reference counting practice can result in crashes in other parts of Tcl that can be difficult to diagnose. 2. C is the only language binding for the Tcl API (although "C" in this case typically includes derivatives such as [C++]), unless you count some tools that use assembly language or things like [ffidl]. 3. The C API may change overtime, and tends to change more than the Tcl script-level interface. 4. Depending on what part of the API you use or require (for an extension library), you may find that Tclkit doesn't work, because the tclInt.h functions used are not in the stubs table. ======c #include #include #include int AddObjCmd (ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) { long n1; long n2; Tcl_Obj *res; /*The command name is objv[0] so 3 arguments are expected.*/ if (3 != objc) { Tcl_WrongNumArgs (interp, 1, objv, "n1 n2"); return TCL_ERROR; } if (TCL_OK != Tcl_GetLongFromObj (interp, objv[1], &n1)) { /*The error result should be set by Tcl_GetLongFromObj.*/ return TCL_ERROR; } if (TCL_OK != Tcl_GetLongFromObj (interp, objv[2], &n2)) { return TCL_ERROR; } res = Tcl_NewLongObj (n1 + n2); Tcl_SetObjResult (interp, res); return TCL_OK; } int main (int argc, char *argv[]) { Tcl_Interp *interp; /* * This finds Tcl's library files and performs some initialization. */ Tcl_FindExecutable (argv[0]); interp = Tcl_CreateInterp (); if (TCL_OK != Tcl_Init (interp)) { fprintf (stderr, "Tcl_Init error: %s\n", Tcl_GetStringResult (interp)); exit (EXIT_FAILURE); } Tcl_CreateObjCommand (interp, "+", AddObjCmd, (ClientData) NULL, (Tcl_CmdDeleteProc *) NULL); while (1) { char cmd[1024]; fgets (cmd, sizeof (cmd), stdin); if (TCL_OK != Tcl_Eval (interp, cmd)) { fprintf (stderr, "error: %s\n", Tcl_GetStringResult (interp)); continue; } printf ("result is: %s\n", Tcl_GetStringResult (interp)); } return EXIT_SUCCESS; } ====== ---- [[explain how to build a [load]'able extension] <
> [[explain how to build an export list for a DLL] <
> [[explain how to link using MSVC++] ** Tcl C API using C++ ** Using C++ with Tcl is similar to using it with C. There are a few tricks to using methods within a class. Within the class we create a wrapper which calls a static function within the class. ======c #include #include /*This is specifically for C++.*/ extern "C" { #include } /*Thanks to Kevin Kenny for his help with this.*/ class Math { public: static int AddObjCmd (ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) { return (reinterpret_cast(clientData))->AddMethod (interp, objc, objv); } int AddMethod (Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]); }; int Math::AddMethod (Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) { long n1; long n2; Tcl_Obj *res; /*The command name is objv[0] so 3 arguments are expected.*/ if (3 != objc) { Tcl_WrongNumArgs (interp, 1, objv, "n1 n2"); return TCL_ERROR; } if (TCL_OK != Tcl_GetLongFromObj (interp, objv[1], &n1)) { /*The error result should be set by Tcl_GetLongFromObj.*/ return TCL_ERROR; } if (TCL_OK != Tcl_GetLongFromObj (interp, objv[2], &n2)) { return TCL_ERROR; } res = Tcl_NewLongObj (n1 + n2); Tcl_SetObjResult (interp, res); return TCL_OK; } int main (int argc, char *argv[]) { Tcl_Interp *interp; /*This finds Tcl's library files and performs some initialization.*/ Tcl_FindExecutable (argv[0]); interp = Tcl_CreateInterp (); if (TCL_OK != Tcl_Init (interp)) { fprintf (stderr, "Tcl_Init error: %s\n", Tcl_GetStringResult (interp)); exit (EXIT_FAILURE); } Math *inst = new Math; Tcl_CreateObjCommand (interp, "+", inst->AddObjCmd, (ClientData) inst, (Tcl_CmdDeleteProc *) NULL); while (1) { char cmd[1024]; fgets (cmd, sizeof (cmd), stdin); if (TCL_OK != Tcl_Eval (interp, cmd)) { fprintf (stderr, "error: %s\n", Tcl_GetStringResult (interp)); continue; } printf ("result is: %s\n", Tcl_GetStringResult (interp)); } return EXIT_SUCCESS; } ====== [[perhaps someone more knowledgeable about C++ could improve this]] [SLB] I'll just comment that the 'tricks' are dangerous. Compiling the above code with Sun's compiler reports: ======none "tclmain.cpp", line 61: Warning (Anachronism): Formal argument proc of type extern "C" int(*)(void*,Tcl_Interp*,int,Tcl_Obj*const*) in call to Tcl_CreateObjCommand(Tcl_Interp*, const char*, extern "C" int(*)(void*,Tcl_Interp*,int,Tcl_Obj*const*), void*, extern "C" void(*)(void*)) is being passed int(*)(void*,Tcl_Interp*,int,Tcl_Obj*const*). ====== I don't have a reference to the relavent clause in the C++ standard to hand but warnings about portability problems from treating C and C++ function pointers as interchangeable are widespread. See for example [http://mail.gnome.org/archives/gtk-list/1999-December/msg00424.html] Links: 1. ftp://ftp.forwiss.uni-passau.de/pub/Os/Unix/languages/tcl/extensions/tkmin/ [[Does this URL work, just very slowly, or is it no longer valid?]] 1. http://www.uni-frankfurt.de/%7Efp/Tcl/tcl-c++.txt [[This URL doesn't appear to be working]] 1. http://prdownloads.sourceforge.net/incrtcl/sampleItclExtension1.1.zip?download ** Tcl C API using Objective-C ** To expose an Objective-C class to Tcl we can create a wrapper in much the same was as was done with C++ earlier. Compile this code using something like: ======none gcc tcl_objc.m -lobjc -I/usr/pkg/include -L/usr/pkg/lib -ltcl84 -lm -lpthread -Wl,-rpath -Wl,/usr/pkg/lib ====== '''tcl_objc.h:''' ======c /* * By George Peter Staplin * This is version 2, and much better than the previous code I put here... */ #include #include #include #include @interface Adder : Object { /* This is just a pointless instance variable. */ int lastresult; } - (int) add:(Tcl_Interp *)interp x:(Tcl_Obj *)x y:(Tcl_Obj *)y; @end int AdderWrapper (ClientData, Tcl_Interp *, int, Tcl_Obj *CONST[]); ====== '''tcl_objc.m:''' ======c #include "tcl_objc.h" @implementation Adder - (int)add:(Tcl_Interp *)interp x:(Tcl_Obj *)x y:(Tcl_Obj *)y { int a, b; if (TCL_OK != Tcl_GetIntFromObj (interp, x, &a)) return TCL_ERROR; if (TCL_OK != Tcl_GetIntFromObj (interp, y, &b)) return TCL_ERROR; Tcl_SetObjResult (interp, Tcl_NewIntObj (lastresult = a + b)); return TCL_OK; } @end int AdderWrapper ( ClientData cdata, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) { id inst = (id) cdata; if (TCL_OK != [inst add: interp x: objv[1] y: objv[2]]) { return TCL_ERROR; } return TCL_OK; } int main (int argc, char *argv[]) { Tcl_Interp *interp; id inst; Tcl_FindExecutable (argv[0]); interp = Tcl_CreateInterp (); if (TCL_OK != Tcl_Init (interp)) { fprintf (stderr, "Tcl_Init error: '%s'\n", Tcl_GetStringResult (interp)); return EXIT_FAILURE; } inst = [Adder new]; Tcl_CreateObjCommand (interp, "add", AdderWrapper, (ClientData) inst, (Tcl_CmdDeleteProc *) NULL); if (TCL_OK != Tcl_Eval (interp, "add 200 123")) { fprintf (stderr, "Tcl_Eval error: '%s'\n", Tcl_GetStringResult (interp)); return EXIT_FAILURE; } printf ("Success: the result of add 200 123 is: %s\n", Tcl_GetStringResult (interp)); return EXIT_SUCCESS; } ====== ---- [jcw] 2003-01-15: Your "add" example above in Critcl: ====== package require critcl critcl::cproc addup {long a long b} long { return a + b; } interp alias {} + {} addup puts "123 + 864 = [+ 123 864]" ====== If you have tclkit and the critcl starkit, do: ====== $ critcl add.tcl 123 + 864 = 987 ====== If you want to turn this into a loadable package, use this code instead: ====== package provide add 1.0 package require critcl critcl::cproc addup {long a long b} long { return a + b; } ====== Then use the -pkg flag: ====== $ critcl -pkg add.tcl Source: add.tcl Library: add.so Package: /home/jcw/lib/add $ ====== The result is a self-contained auto-generated package: ======none $ ls -lR lib/add/ lib/add/: total 9 drwxr-xr-x 2 jcw users 104 Jan 15 18:52 Linux-x86 -rw-r--r-- 1 jcw users 1506 Jan 15 18:52 critcl.tcl -rw-r--r-- 1 jcw users 64 Jan 15 18:52 pkgIndex.tcl lib/add/Linux-x86: total 12 -rwxr-xr-x 1 jcw users 4660 Jan 15 18:50 add.so -rw-r--r-- 1 jcw users 157 Jan 15 18:52 critcl.tcl $ ====== ** Walk-Through Tcl extension ** After writing the desired function in [C], add some initialisation code to register the shared object's functions with Tcl, either `Tcl_CreateCommand` or better, `Tcl_CreateObjCommand`. The initialisation required in the code that compiles to make tclext.dll (the `Tclext_Init` name is composed from the dll name by Tcl): ======c // this is your useful procedure. It can be a C++ or C linked procedure. int tclextfunction (ClientData clientData, Tcl_Interp *interp, int argc, char *argv[]) { // dosomething - clientdata is a pointer to something the programmer may or may not define return TCL_OK; } #ifdef __cplusplus extern "C" { #endif int PROBE_EXPORT Tclext_Init(Tcl_Interp *interp) { // tcl stubs and tk stubs are needed for dynamic loading, you must have this set as a compiler option #ifdef USE_TCL_STUBS if (Tcl_InitStubs(interp, TCL_VERSION, 1) == NULL) { Tcl_SetResult(interp, "Tcl_InitStubs failed",TCL_STATIC); return TCL_ERROR; } #endif #ifdef USE_TK_STUBS if (Tk_InitStubs(interp, TCL_VERSION, 1) == NULL) { Tcl_SetResult(interp, "Tk_InitStubs failed",TCL_STATIC); return TCL_ERROR; } #endif Tcl_CreateCommand( "tclextfunction", tclextfunction ); // register your functions with Tcl return TCL_OK; } #ifdef __cplusplus } #endif ====== Then in Tcl script use ====== load tclext.dll tclextfunction a b c ====== to pass the strings a,b,c to tclextfunction in the array argv - argc will be 3 of course. The ClientData is a pointer to anything (perhaps a global data structure or a class defined by a ClientData statement often dynamically allocated in the `Tclext_Init` function). <> Tutorial