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Tcl_CreateCommand(3) Tcl Library Procedures Tcl_CreateCommand(3)
Tcl_CreateCommand - implement new commands in C
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
Tcl_CmdDeleteProc *deleteProc (in) Procedure to call before
cmdName is deleted from the
interpreter; allows for
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(
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
typedef void Tcl_CmdDeleteProc(
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