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
                                                       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  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
       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 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
       subsequent  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 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  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_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_SetCommandInfo,
       Tcl_GetCommandName, Tcl_SetObjResult

KEYWORDS

       bind, command, create, delete, interpreter, namespace