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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
						       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,
		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  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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