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  4. Tcl_CreateCommand(3)

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Tcl_CreateCommand(3) Tcl Library Procedures Tcl_CreateCommand(3) 





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 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
    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
    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







  

    
    Tcl