Extending Tcl is a guide to writing Tcl extensions.
For information at building Tcl extension using Cygnus's Cygwin environment, take a look at the following files:
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 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:
#include <tcl.h> 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" )
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; }
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
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:
Con:
/* * By George Peter Staplin * This is version 2 of a simple executable-module written in C. * This is simply a demonstration. */ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <limits.h> #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
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 loaded 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:
Con:
#include <stdio.h> #include <stdlib.h> #include <tcl.h> 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++]
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.
#include <stdio.h> #include <stdlib.h> /*This is specifically for C++.*/ extern "C" { #include <tcl.h> } /*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<Math*>(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:
"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 [L2 ]
Links:
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:
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:
/* * By George Peter Staplin * This is version 2, and much better than the previous code I put here... */ #include <stdio.h> #include <stdlib.h> #include <tcl.h> #include <objc/Object.h> @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:
#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:
$ 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 $
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):
// 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).