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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 command:  proc will be
						   called whenever cmdName is invoked as  a  com-
						   mand.

       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-spe-
						   cific 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 pro-
       cedures 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 sub-
       sequent	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 addi-
       tion, 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  set-
       ting  the  return value;  for complete details on how the interpreter result field is man-
       aged, 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_Cre-
       ateCommand.   DeleteProc  is invoked before the command is deleted, and gives the applica-
       tion 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_Create-
       Command.

SEE ALSO
       Tcl_CreateObjCommand, Tcl_DeleteCommand, Tcl_GetCommandInfo, Tcl_SetCommandInfo,  Tcl_Get-
       CommandName, Tcl_SetObjResult

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

Tcl									     Tcl_CreateCommand(3)
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