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NAME
Tcl_CreateObjCommand, Tcl_DeleteCommand,
Tcl_DeleteCommandFromToken, Tcl_GetCommandInfo,
Tcl_SetCommandInfo, Tcl_GetCommandName - implement new com-
mands in C
SYNOPSIS
#include <tcl.h>
Tcl_Command
Tcl_CreateObjCommand(interp, cmdName, proc, clientData, deleteProc)
int
Tcl_DeleteCommand(interp, cmdName)
int
Tcl_DeleteCommandFromToken(interp, token)
int
Tcl_GetCommandInfo(interp, cmdName, infoPtr)
int
Tcl_SetCommandInfo(interp, cmdName, infoPtr)
char *
Tcl_GetCommandName(interp, token)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter in
which to create a
new command or that
contains a command.
char *cmdName (in) Name of command.
Tcl_ObjCmdProc *proc (in) Implementation of
the 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
interpreter; allows
for command-
specific cleanup.
If NULL, then no
procedure is called
before the command
is deleted.
Tcl_Command token (in) Token for command,
returned by previ-
ous call to
Tcl_CreateObjCommand.
The command must
not have been
deleted.
Tcl_CmdInfo *infoPtr (in/out) Pointer to struc-
ture containing
various information
about a Tcl com-
mand.
_________________________________________________________________
DESCRIPTION
Tcl_CreateObjCommand defines a new command in interp and
associates it with procedure proc such that whenever name is
invoked as a Tcl command (e.g., via a call to Tcl_EvalObj)
the Tcl interpreter will call proc to process the command.
Tcl_CreateObjCommand deletes any existing command name
already associated with the interpreter (however see below
for an exception where the existing command is not deleted).
It returns a token that may be used to refer to the command
in subsequent calls to Tcl_GetCommandName. If name contains
any :: namespace qualifiers, then the command is added to
the specified namespace; otherwise the command is added to
the global namespace. If Tcl_CreateObjCommand 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_ObjCmdProc:
typedef int Tcl_ObjCmdProc(
ClientData clientData,
Tcl_Interp *interp,
int objc,
Tcl_Obj *CONST objv[]); |
When proc is invoked, the clientData and interp parameters |
will be copies of the clientData and interp arguments given |
to Tcl_CreateObjCommand. Typically, clientData points to an |
application-specific data structure that describes what to |
do when the command procedure is invoked. Objc and objv |
describe the arguments to the command, objc giving the |
number of argument objects (including the command name) and |
objv giving the values of the arguments. The objv array |
will contain objc values, pointing to the argument objects. |
Unlike argv[argv] used in a string-based command procedure, |
objv[objc] will not contain NULL. |
Additionally, when proc is invoked, it must not modify the |
contents of the objv array by assigning new pointer values |
to any element of the array (for example, objv[2] = NULL) |
because this will cause memory to be lost and the runtime |
stack to be corrupted. The CONST in the declaration of objv |
will cause ANSI-compliant compilers to report any such |
attempted assignment as an error. However, it is acceptable |
to modify the internal representation of any individual |
object argument. For instance, the user may call |
Tcl_GetIntFromObj on objv[2] to obtain the integer represen- |
tation of that object; that call may change the type of the |
object that objv[2] points at, but will not change where |
objv[2] points.
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, if proc needs to return a non-empty result, it
can call Tcl_SetObjResult to set the interpreter's result.
In the case of a TCL_OK return code this gives the result of
the command, and in the case of TCL_ERROR this gives an
error message. Before invoking a command procedure,
Tcl_EvalObj sets interpreter's result to point to an object
representing an empty string, so simple commands can return
an empty result by doing nothing at all.
The contents of the objv array belong to Tcl and are not
guaranteed to persist once proc returns: proc should not
modify them. Call Tcl_SetObjResult if you want to return
something from the objv array.
Ordinarily, Tcl_CreateObjCommand deletes any existing com-
mand name already associated with the interpreter. However,
if the existing command was created by a previous call to
Tcl_CreateCommand, Tcl_CreateObjCommand does not delete the
command but instead arranges for the Tcl interpreter to call
the Tcl_ObjCmdProc proc in the future. The old string-based
Tcl_CmdProc associated with the command is retained and its
address can be obtained by subsequent Tcl_GetCommandInfo
calls. This is done for backwards compatibility.
DeleteProc will be invoked when (if) name is deleted. This
can occur through a call to Tcl_DeleteCommand,
Tcl_DeleteCommandFromToken, or Tcl_DeleteInterp, or by
replacing name in another call to Tcl_CreateObjCommand.
DeleteProc is invoked before the command is deleted, and
gives the application an opportunity to release any struc-
tures 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_CreateObjCommand.
Tcl_DeleteCommand deletes a command from a command inter-
preter. 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 restric-
tions on cmdName: it may refer to a built-in command, an
application-specific command, or a Tcl procedure. If name
contains any :: namespace qualifiers, the command is deleted
from the specified namespace.
Given a token returned by Tcl_CreateObjCommand,
Tcl_DeleteCommandFromToken deletes the command from a com-
mand interpreter. It will delete a command even if that
command has been renamed. Once the call completes, attempts
to invoke the command in interp will result in errors. If
the command corresponding to token has already been deleted
from interp then Tcl_DeleteCommand does nothing and returns
-1; otherwise it returns 0.
Tcl_GetCommandInfo checks to see whether its cmdName argu-
ment exists as a command in interp. cmdName may include ::
namespace qualifiers to identify a command in a particular
namespace. If the command is not found, then it returns 0.
Otherwise it places information about the command in the
Tcl_CmdInfo structure pointed to by infoPtr and returns 1.
A Tcl_CmdInfo structure has the following fields:
typedef struct Tcl_CmdInfo {
int isNativeObjectProc;
Tcl_ObjCmdProc *objProc;
ClientData objClientData;
Tcl_CmdProc *proc;
ClientData clientData;
Tcl_CmdDeleteProc *deleteProc;
ClientData deleteData;
Tcl_Namespace *namespacePtr;
} Tcl_CmdInfo;
The isNativeObjectProc field has the value 1 if
Tcl_CreateObjCommand was called to register the command; it
is 0 if only Tcl_CreateCommand was called. It allows a pro-
gram to determine whether it is faster to call objProc or
proc: objProc is normally faster if isNativeObjectProc has
the value 1. The fields objProc and objClientData have the
same meaning as the proc and clientData arguments to
Tcl_CreateObjCommand; they hold information about the
object-based command procedure that the Tcl interpreter
calls to implement the command. The fields proc and client-
Data hold information about the string-based command pro-
cedure that implements the command. If Tcl_CreateCommand
was called for this command, this is the procedure passed to
it; otherwise, this is a compatibility procedure registered
by Tcl_CreateObjCommand that simply calls the command's
object-based procedure after converting its string arguments
to Tcl objects. The field deleteData 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. The field namespacePtr holds
a pointer to the Tcl_Namespace that contains the command.
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. cmdName may
include :: namespace qualifiers to identify a command in a
particular namespace. 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. Note that Tcl_SetCmdInfo will not change a
command's namespace; you must use Tcl_RenameCommand to do
that.
Tcl_GetCommandName provides a mechanism for tracking com-
mands that have been renamed. Given a token returned by
Tcl_CreateObjCommand 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. This name does
not include any :: namespace qualifiers. 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.
SEE ALSO
Tcl_CreateCommand, Tcl_ResetResult, Tcl_SetObjResult
KEYWORDS
bind, command, create, delete, namespace, object
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