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Tcl_CreateCommand(3)	    Tcl	Library	Procedures	  Tcl_CreateCommand(3)

______________________________________________________________________________

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  com-
						   mand:   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 com-
						   mand	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 com-
       mand  (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 values.  The
       value-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 values  as
       arguments  and  those values can	retain an internal representation that
       can be manipulated more efficiently.  Also, Tcl's interpreter now  uses
       values 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 value before the call.	 New  commands
       should  be  defined using Tcl_CreateObjCommand.	We support Tcl_Create-
       Command for backwards compatibility.

       The procedures Tcl_DeleteCommand, Tcl_GetCommandInfo,  and  Tcl_SetCom-
       mandInfo	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_GetCommand-
       Name.  If cmdName contains any :: namespace qualifiers, then  the  com-
       mand  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_CreateCom-
       mand.   Typically,  clientData  points  to an application-specific data
       structure that describes	what to	do when	the command procedure  is  in-
       voked.	Argc and argv describe the arguments to	the command, argc giv-
       ing the number of arguments (including the command name)	and argv  giv-
       ing  the	 values	of the arguments as strings.  The argv array will con-
       tain 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; 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	inter-
       face for	setting	the return value;  for complete	details	on how the in-
       terpreter 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 some-
       thing 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 replac-
       ing cmdName in another call to Tcl_CreateCommand.   DeleteProc  is  in-
       voked  before  the command is deleted, and gives	the application	an op-
       portunity 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_Set-
       CommandInfo, Tcl_GetCommandName,	Tcl_SetObjResult

KEYWORDS
       bind, command, create, delete, interpreter, namespace

Tcl							  Tcl_CreateCommand(3)

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