Tcl_CreateObjCommand(3)Tcl
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NAME
Tcl_CreateObjCommand, Tcl_DeleteCommand, Tcl_DeleteCom-
mandFromToken, Tcl_GetCommandInfo, Tcl_SetCommandInfo,
Tcl_GetCommandName - implement new commands 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 com-
mand-specific
cleanup. If NULL,
then no procedure
is called before
the command is
deleted.
Tcl_Command token (in) Token for com-
mand, returned by
previous call to
Tcl_CreateObjCom-
mand. The com-
mand must not
have been
deleted.
Tcl_CmdInfo *infoPtr (in/out) Pointer to struc-
ture containing
various informa-
tion about a Tcl
command.
_________________________________________________________________
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_Eval-
Obj) the Tcl interpreter will call proc to process the
command.
Tcl_CreateObjCommand will delete any command name 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 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_GetIntFromObject on objv[2] to obtain the integer |
representation 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 noth-
ing 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.
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_Cmd-
DeleteProc:
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
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 pro-
cedure. 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 noth-
ing 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 partic-
ular namespace. If the command is not found, then it
returns 0. Otherwise it places information about the com-
mand 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_Cre-
ateObjCommand was called to register the command; it is 0
if only Tcl_CreateCommand was called. It allows a program
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
clientData hold information about the string-based command
procedure that implements the command. If Tcl_CreateCom-
mand 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 indepen-
dently 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_RenameCom-
mand 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