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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
       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 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; 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 inter‐
       preter 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
       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_Set‐
       CommandInfo, Tcl_GetCommandName, Tcl_SetObjResult

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

Tcl							  Tcl_CreateCommand(3)
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