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CrtCommand

Tcl_CreateCommand(3)        Tcl Library Procedures        Tcl_CreateCommand(3)



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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.

       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 inter-
                                                       preter; allows for com-
                                                       mand-specific  cleanup.
                                                       If NULL, then no proce-
                                                       dure is  called  before
                                                       the command is deleted.
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DESCRIPTION
       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-
       patibility.

       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
       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_Set-
       CommandInfo, Tcl_GetCommandName, Tcl_SetObjResult


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



Tcl                                                       Tcl_CreateCommand(3)