DOKK / manpages / debian 10 / tcl8.6-doc / Tcl_CreateCommand.3tcl.en
Tcl_CreateCommand(3tcl) Tcl Library Procedures Tcl_CreateCommand(3tcl) 







Tcl_CreateCommand - implement new commands in C








#include <tcl.h>

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









  
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.
    
    

    

  










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.








Tcl_CreateObjCommand, Tcl_DeleteCommand, Tcl_GetCommandInfo,
    Tcl_SetCommandInfo, Tcl_GetCommandName, Tcl_SetObjResult








bind, command, create, delete, interpreter, namespace







  

    
    Tcl