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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.

       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‐

       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 inter‐
						       preter; allows for com‐
						       mand-specific  cleanup.
						       If NULL, then no proce‐
						       dure is	called	before
						       the command 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
       objects as arguments and those objects can retain an internal represen‐
       tation  that  can  be manipulated more efficiently.  Also, Tcl's inter‐
       preter 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,
		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.

       Proc  must  return  an  integer	code that is either 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  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 setting the return value;	for complete  details  on  how
       the  the	 interpreter  result  field is managed, see the Tcl_Interp man
       page.  Before invoking a command procedure, Tcl_Eval  sets  the	inter‐
       preter  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
       replacing 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
	      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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