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 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_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  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
       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 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