Provided by: tcl8.5-doc_8.5.19-4_all 
NAME
Tcl_CreateCommand - implement new commands in C
SYNOPSIS
#include <tcl.h>
Tcl_Command
Tcl_CreateCommand(interp, cmdName, proc, clientData, deleteProc)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter in which to create new command.
const char *cmdName (in) Name of command.
Tcl_CmdProc *proc (in) Implementation of new command: proc will be
called whenever cmdName is invoked as a
command.
ClientData clientData (in) Arbitrary one-word value to pass to proc and
deleteProc.
Tcl_CmdDeleteProc *deleteProc (in) 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
Tcl_CreateCommand defines a new command in interp and associates it with procedure proc
such that whenever cmdName is invoked as a Tcl command (via a call to Tcl_Eval) the Tcl
interpreter will call proc to process the command. It differs from Tcl_CreateObjCommand
in that a new string-based command is defined; that is, a command procedure is defined
that takes an array of argument strings instead of objects. The object-based command
procedures registered by Tcl_CreateObjCommand can execute significantly faster than the
string-based command procedures defined by Tcl_CreateCommand. This is because they take
Tcl objects as arguments and those objects can retain an internal representation that can
be manipulated more efficiently. Also, Tcl's interpreter now uses objects internally. In
order to invoke a string-based command procedure registered by Tcl_CreateCommand, it must
generate and fetch a string representation from each argument object before the call and
create a new Tcl object to hold the string result returned by the string-based command
procedure. New commands should be defined using Tcl_CreateObjCommand. We support
Tcl_CreateCommand for backwards compatibility.
The procedures Tcl_DeleteCommand, Tcl_GetCommandInfo, and Tcl_SetCommandInfo are used in
conjunction with Tcl_CreateCommand.
Tcl_CreateCommand will delete an existing command cmdName, if one is already associated
with the interpreter. It returns a token that may be used to refer to the command in
subsequent calls to Tcl_GetCommandName. If cmdName contains any :: namespace qualifiers,
then the command is added to the specified namespace; otherwise the command is added to
the global namespace. If Tcl_CreateCommand is called for an interpreter that is in the
process of being deleted, then it does not create a new command and it returns NULL. Proc
should have arguments and result that match the type Tcl_CmdProc:
typedef int Tcl_CmdProc(
ClientData clientData,
Tcl_Interp *interp,
int argc,
const char *argv[]);
When proc is invoked the clientData and interp parameters will be copies of the clientData
and interp arguments given to Tcl_CreateCommand. Typically, clientData points to an
application-specific data structure that describes what to do when the command procedure
is invoked. Argc and argv describe the arguments to the command, argc giving the number
of arguments (including the command name) and argv giving the values of the arguments as
strings. The argv array will contain argc+1 values; the first argc values point to the
argument strings, and the last value is NULL. Note that the argument strings should not
be modified as they may point to constant strings or may be shared with other parts of the
interpreter.
Note that the argument strings are encoded in normalized UTF-8 since version 8.1 of Tcl.
Proc must return an integer code that is expected to be one of TCL_OK, TCL_ERROR,
TCL_RETURN, TCL_BREAK, or TCL_CONTINUE. See the Tcl overview man page for details on what
these codes mean. Most normal commands will only return TCL_OK or TCL_ERROR. In
addition, proc must set the interpreter result to point to a string value; in the case of
a TCL_OK return code this gives the result of the command, and in the case of TCL_ERROR it
gives an error message. The Tcl_SetResult procedure provides an easy interface for
setting the return value; for complete details on how the interpreter result field is
managed, see the Tcl_Interp man page. Before invoking a command procedure, Tcl_Eval sets
the interpreter result to point to an empty string, so simple commands can return an empty
result by doing nothing at all.
The contents of the argv array belong to Tcl and are not guaranteed to persist once proc
returns: proc should not modify them, nor should it set the interpreter result to point
anywhere within the argv values. Call Tcl_SetResult with status TCL_VOLATILE if you want
to return something from the argv array.
DeleteProc will be invoked when (if) cmdName is deleted. This can occur through a call to
Tcl_DeleteCommand or Tcl_DeleteInterp, or by replacing cmdName in another call to
Tcl_CreateCommand. DeleteProc is invoked before the command is deleted, and gives the
application an opportunity to release any structures associated with the command.
DeleteProc should have arguments and result that match the type Tcl_CmdDeleteProc:
typedef void Tcl_CmdDeleteProc(
ClientData clientData);
The clientData argument will be the same as the clientData argument passed to
Tcl_CreateCommand.
SEE ALSO
Tcl_CreateObjCommand, Tcl_DeleteCommand, Tcl_GetCommandInfo, Tcl_SetCommandInfo,
Tcl_GetCommandName, Tcl_SetObjResult
KEYWORDS
bind, command, create, delete, interpreter, namespace