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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.

       void *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(
		      void *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	inter-
       preter.	Note also 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  return  man
       page  for details on what these codes mean and the use of extended val-
       ues for an extension's private use. Most	normal commands	will only  re-
       turn 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	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 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(
		      void *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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