Tcl_CreateCommand(3)        Tcl Library Procedures        Tcl_CreateCommand(3)


       Tcl_CreateCommand, Tcl_DeleteCommand, Tcl_GetCommandInfo,
       Tcl_SetCommandInfo - implement new commands in C

       #include <tcl.h>

       Tcl_CreateCommand(interp, cmdName, proc, clientData, deleteProc)

       Tcl_DeleteCommand(interp, cmdName)

       Tcl_GetCommandInfo(interp, cmdName, infoPtr)

       Tcl_SetCommandInfo(interp, cmdName, infoPtr)

       char *
       Tcl_GetCommandName(interp, token)

       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

       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
                                                       cleanup.  If NULL, then
                                                       no procedure is called
                                                       before the command is

       Tcl_CmdInfo         *infoPtr          (in/out)  Pointer to structure
                                                       containing various
                                                       information about a Tcl

       Tcl_Command         token             (in)      Token for command,
                                                       returned by previous
                                                       call to
                                                       Tcl_CreateCommand.  The
                                                       command must not have
                                                       been deleted.

       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.  If there is already a command cmdName associated
       with the interpreter, it is deleted.  Tcl_CreateCommand returns a token
       that may be used to refer to the command in subsequent calls to
       Tcl_GetCommandName.  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_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.

       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 interp->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 interp->result field is managed, see the Tcl_Interp man page.
       Before invoking a command procedure, Tcl_Eval sets interp->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 interp->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
              typedef void Tcl_CmdDeleteProc(ClientData clientData);
       The clientData argument will be the same as the clientData argument
       passed to Tcl_CreateCommand.

       Tcl_DeleteCommand deletes a command from a command interpreter.  Once
       the call completes, attempts to invoke cmdName in interp will result in
       errors.  If cmdName isn't bound as a command in interp then
       Tcl_DeleteCommand does nothing and returns -1;  otherwise it returns 0.
       There are no restrictions on cmdName:  it may refer to a built-in
       command, an application-specific command, or a Tcl procedure.

       Tcl_GetCommandInfo checks to see whether its cmdName argument exists as
       a command in interp.  If not then it returns 0.  Otherwise it places
       information about the command in the structure pointed to by infoPtr
       and returns 1.  Tcl_CmdInfo structures have fields named proc,
       clientData, and deleteProc, which have the same meaning as the
       corresponding arguments to Tcl_CreateCommand.  There is also a field
       deleteData, which is the ClientData value to pass to deleteProc;  it is
       normally the same as clientData but may be set independently using the
       Tcl_SetCommandInfo procedure.

       Tcl_SetCommandInfo is used to modify the procedures and ClientData
       values associated with a command.  Its cmdName argument is the name of
       a command in interp.  If this command does not exist then
       Tcl_SetCommandInfo returns 0.  Otherwise, it copies the information
       from *infoPtr to Tcl's internal structure for the command and returns
       1.  Note that this procedure allows the ClientData for a command's
       deletion procedure to be given a different value than the ClientData
       for its command procedure.

       Tcl_GetCommandName provides a mechanism for tracking commands that have
       been renamed.  Given a token returned by Tcl_CreateCommand when the
       command was created, Tcl_GetCommandName returns the string name of the
       command.  If the command has been renamed since it was created, then
       Tcl_GetCommandName returns the current name.  The command corresponding
       to token must not have been deleted.  The string returned by
       Tcl_GetCommandName is in dynamic memory owned by Tcl and is only
       guaranteed to retain its value as long as the command isn't deleted or
       renamed;  callers should copy the string if they need to keep it for a
       long time.

       bind, command, create, delete, interpreter

Tcl                                                       Tcl_CreateCommand(3)