SWIG , or Simplified Wrapper and Interface Generator, by Dave Beazley, generates Tcl C interfaces C and C++ code.
SWIG automates the generation of interfaces in various languages, including Tcl, to functions written in C/C++. SWIG reads ANSI C/C++ declarations and builds a an interface in the target language. SWIG is avalable for Unix-like systems and also for Windows
The idea of Swig is to provide a tool that can, with hopefully little pain, allow one to create glue code between general libraries and various scripting languages, one of which is Tcl. Swig can be used for C++ or C libraries - making it one of the first places people are recommended to look when dealing with legacy libraries.
Benefits and uses of SWIG:
To contrast SWIG with Objectify - SWIG has you prepare a small interface file that specifies what functions are to be wrapped, rather than adding macros to your original header file. It also works with C, as well as C++.
If you look around in books or places like Cameron Laird's Tcl pages [L1 ] you can find a lot of information about integrating Tcl with C. That's all fine and dandy if you're going to write the interface code by hand.
But if you want a nice example of how you ought to write your wrappers to call C or C++ from Tcl, then you can't go wrong looking at the code generated by SWIG. David Beazley did a great job of implementing both the old Tcl 7.x all-string interface and the Tcl 8.x object interface. Modern versions of SWIG (since 1.3a5) do not support the Tcl 7.x interface.
For example, a short little function like this:
double convert ( int *value, char *targetUnits );
gets wrapped by SWIG with this code for Tcl 8.x:
static int _wrap_convert(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
double _result;
int * _arg0;
char * _arg1;
Tcl_Obj * tcl_result;
char * rettype;
int templength;
clientData = clientData; objv = objv;
tcl_result = Tcl_GetObjResult(interp);
if ((objc < 3) || (objc > 3)) {
Tcl_SetStringObj(tcl_result,"Wrong # args. convert value targetUnits ",-1);
return TCL_ERROR;
}
if ((rettype = SWIG_GetPointerObj(interp,objv[1],(void **) &_arg0,"_int_p"))) {
Tcl_SetStringObj(tcl_result, "Type error in argument 1 of convert. Expected _int_p, received ", -1);
Tcl_AppendToObj(tcl_result, rettype, -1);
return TCL_ERROR;
}
if ((_arg1 = Tcl_GetStringFromObj(objv[2], &templength)) == NULL) return TCL_ERROR;
_result = (double )convert(_arg0,_arg1);
tcl_result = Tcl_GetObjResult(interp);
Tcl_SetDoubleObj(tcl_result,(double) _result);
return TCL_OK;
}If you're using SWIG 1.1 or earlier, it also supported the 7.x interface model:
static int _wrap_convert(ClientData clientData, Tcl_Interp *interp, int argc, char *argv[]) {
double _result;
int * _arg0;
char * _arg1;
clientData = clientData; argv = argv;
if ((argc < 3) || (argc > 3)) {
Tcl_SetResult(interp, "Wrong # args. convert value targetUnits ",TCL_STATIC);
return TCL_ERROR;
}
if (SWIG_GetPtr(argv[1],(void **) &_arg0,"_int_p")) {
Tcl_SetResult(interp, "Type error in argument 1 of convert. Expected _int_p, received ", TCL_STATIC);
Tcl_AppendResult(interp, argv[1], (char *) NULL);
return TCL_ERROR;
}
_arg1 = argv[2];
_result = (double )convert(_arg0,_arg1);
Tcl_PrintDouble(interp,(double) _result, interp->result);
return TCL_OK;
}As of SWIG 1.3.40, the generated C/C++ wrapper will use the Stubs feature if compiled with -DUSE_TK_STUBS. Also, you can override the minimum version to support which is passed to Tcl_InitStubs() and Tk_InitStubs() with -DSWIG_TCL_STUBS_VERSION="8.3" or the version being compiled with using -DSWIG_TCL_STUBS_VERSION=TCL_VERSION.
AMG: I'd like the ability to unload a Swig extension, but the latest CVS only provides xxx_Init() and xxx_SafeInit(). Any suggestions?
2011-04-13: David Beazley: "... life is too short to wrap my brain around the ever-growing pile of hacks called C++. ... things like this are why I don't work on swig anymore."