CrtObjCmd
Tcl_CreateObjCommand(3) Tcl Library Procedures Tcl_CreateObjCommand(3)
______________________________________________________________________________
NAME
Tcl_CreateObjCommand, Tcl_DeleteCommand, Tcl_DeleteCommandFromToken,
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 com-
mand: 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 cmd-
Name 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 command, returned by
previous call to Tcl_CreateOb-
jCommand. The command must
not have been deleted.
Tcl_CmdInfo *infoPtr (in/out) Pointer to structure contain-
ing various information 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_EvalObjEx) the Tcl interpreter will call proc
to process the command.
Tcl_CreateObjCommand deletes any existing command name already associ-
ated 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 com-
mand 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_CreateObj- |
Command. 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 giv- |
ing 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 decla- |
ration 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 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_EvalObjEx 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_SetO-
bjResult if you want to return something from the objv array.
Ordinarily, Tcl_CreateObjCommand deletes any existing command name
already associated with the interpreter. However, if the existing com-
mand was created by a previous call to Tcl_CreateCommand, Tcl_CreateOb-
jCommand 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_CreateOb-
jCommand. DeleteProc is invoked before the command is deleted, and
gives the application an opportunity to release any structures associ-
ated 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 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 com-
mand, 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_DeleteCommandFrom-
Token deletes the command from a command interpreter. It will delete a
command even if that command has been renamed. Once the call com-
pletes, 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 argument 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 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_CreateCommand was called for this
command, this is the procedure passed to it; otherwise, this is a com-
patibility 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 val-
ues 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 commands 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_GetCom-
mandName 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
Tcl 8.0 Tcl_CreateObjCommand(3)
