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Tcl_CreateCommand(3)	    Tcl	Library	Procedures	  Tcl_CreateCommand(3)


       Tcl_CreateCommand - implement new commands in C

       #include	<tcl.h>

       Tcl_CreateCommand(interp, cmdName, proc,	clientData, deleteProc)

       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

       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.

       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  objects.
       The  object-based command procedures registered by Tcl_CreateObjCommand
       can execute significantly faster	than the string-based  command	proce-
       dures  defined by Tcl_CreateCommand.  This is because they take Tcl ob-
       jects as	arguments and those objects can	retain an internal representa-
       tion 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 com-

       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 over-
       view man	page for details on what these codes mean.  Most  normal  com-
       mands 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	proce-
       dure provides an	easy interface for setting the return value;  for com-
       plete 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 com-
       mands 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 oc-
       cur through a call to Tcl_DeleteCommand or Tcl_DeleteInterp, or by  re-
       placing	cmdName	 in  another call to Tcl_CreateCommand.	 DeleteProc is
       invoked 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
	      typedef void Tcl_CmdDeleteProc(
		      ClientData clientData);
       The  clientData	argument  will	be the same as the clientData argument
       passed to Tcl_CreateCommand.

       Tcl_CreateObjCommand, Tcl_DeleteCommand,	 Tcl_GetCommandInfo,  Tcl_Set-
       CommandInfo, Tcl_GetCommandName,	Tcl_SetObjResult

       bind, command, create, delete, interpreter, namespace

Tcl							  Tcl_CreateCommand(3)


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