Itcl_RegisterC(3) [incr Tcl] Library Procedures Itcl_RegisterC(3)NAME
Itcl_RegisterC, Itcl_RegisterObjC, Itcl_FindC - Associate a symbolic
name with a C procedure.
SYNOPSIS
#include <itcl.h>
int
Itcl_RegisterC(interp, cmdName, argProc, clientData, deleteProc)
int
Itcl_RegisterObjC(interp, cmdName, objProc, clientData, deleteProc)
int
Itcl_FindC(interp, cmdName, argProcPtr, objProcPtr, cDataPtr)
ARGUMENTS
Interpreter in which to create new command. Name of command. Imple‐
mentation of new command: argProc will be called whenever The Tcl_Cmd‐
Proc * to receive the pointer. Implementation of the new command:
objProc will be called whenever The Tcl_ObjCmdProc * to receive the
pointer. Arbitrary one-word value to pass to proc and deleteProc. The
ClientData to receive the pointer. Procedure to call before cmdName is
deleted from the interpreter; allows for command-specific cleanup. If
NULL, then no procedure is called before the command is deleted.
DESCRIPTION
Used to associate a symbolic name with an (argc,argv) C procedure that
handles a Tcl command. Procedures that are registered in this manner
can be referenced in the body of an [incr Tcl] class definition to
specify C procedures to acting as methods/procs. Usually invoked in an
initialization routine for an extension, called out in Tcl_AppInit() at
the start of an application.
Each symbolic procedure can have an arbitrary client data value associ‐
ated with it. This value is passed into the command handler whenever
it is invoked.
A symbolic procedure name can be used only once for a given style
(arg/obj) handler. If the name is defined with an arg-style handler,
it can be redefined with an obj-style handler; or if the name is
defined with an obj-style handler, it can be redefined with an arg-
style handler. In either case, any previous client data is discarded
and the new client data is remembered. However, if a name is redefined
to a different handler of the same style, this procedure returns an
error.
Returns TCL_OK on success, or TCL_ERROR (along with an error message in
interp->result) if anything goes wrong.
C procedures can be integrated into an [incr Tcl] class definition to
implement methods, procs, and the "config" code for public variables.
Any body that starts with "@" is treated as the symbolic name for a C
procedure.
Symbolic names are established by registering procedures via Itcl_Reg‐
isterC(). This is usually done in the Tcl_AppInit() procedure, which
is automatically called when the interpreter starts up. In the follow‐
ing example, the procedure My_FooCmd() is registered with the symbolic
name "foo". This procedure can be referenced in the body command as
"@foo". int Tcl_AppInit(interp)
Tcl_Interp *interp; /* Interpreter for application. */ {
if (Itcl_Init(interp) == TCL_ERROR) {
return TCL_ERROR;
}
if (Itcl_RegisterC(interp, "foo", My_FooCmd) != TCL_OK) {
return TCL_ERROR;
} } C procedures are implemented just like ordinary Tcl commands.
See the CrtCommand man page for details. Within the procedure, class
data members can be accessed like ordinary variables using Tcl_Set‐
Var(), Tcl_GetVar(), Tcl_TraceVar(), etc. Class methods and procs can
be executed like ordinary commands using Tcl_Eval(). [incr Tcl] makes
this possible by automatically setting up the context before executing
the C procedure.
This scheme provides a natural migration path for code development.
Classes can be developed quickly using Tcl code to implement the bod‐
ies. An entire application can be built and tested. When necessary,
individual bodies can be implemented with C code to improve perfor‐
mance.
See the Archetype class in [incr Tk] for an example of how this C link‐
ing method is used.
SEE ALSO
Tcl_CreateCommand, Tcl_CreateObjCommand
KEYWORDS
class, object
itcl 3.0 Itcl_RegisterC(3)
