path: root/doc/CrtObjCmd.3

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'\" RCS: @(#) $Id: CrtObjCmd.3,v 1.3.12.1 2000/08/07 21:29:37 hobbs Exp $
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.so man.macros
.TH Tcl_CreateObjCommand 3 8.0 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_CreateObjCommand, Tcl_DeleteCommand, Tcl_DeleteCommandFromToken, Tcl_GetCommandInfo, Tcl_SetCommandInfo, Tcl_GetCommandName \- implement new commands in C
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
Tcl_Command
\fBTcl_CreateObjCommand\fR(\fIinterp, cmdName, proc, clientData, deleteProc\fR)
.sp
int
\fBTcl_DeleteCommand\fR(\fIinterp, cmdName\fR)
.sp
int
\fBTcl_DeleteCommandFromToken\fR(\fIinterp, token\fR)
.sp
int
\fBTcl_GetCommandInfo\fR(\fIinterp, cmdName, infoPtr\fR)
.sp
int
\fBTcl_SetCommandInfo\fR(\fIinterp, cmdName, infoPtr\fR)
.sp
char *
\fBTcl_GetCommandName\fR(\fIinterp, token\fR)
.SH ARGUMENTS
.AS Tcl_ObjCmdProc *deleteProc in/out
.AP Tcl_Interp *interp in
Interpreter in which to create a new command or that contains a command.
.AP char *cmdName in
Name of command.
.AP Tcl_ObjCmdProc *proc in
Implementation of the new command: \fIproc\fR will be called whenever
\fIcmdName\fR is invoked as a command.
.AP ClientData clientData in
Arbitrary one-word value to pass to \fIproc\fR and \fIdeleteProc\fR.
.AP Tcl_CmdDeleteProc *deleteProc in
Procedure to call before \fIcmdName\fR is deleted from the interpreter;
allows for command-specific cleanup. If NULL, then no procedure is
called before the command is deleted.
.AP Tcl_Command token in
Token for command, returned by previous call to \fBTcl_CreateObjCommand\fR.
The command must not have been deleted.
.AP Tcl_CmdInfo *infoPtr in/out
Pointer to structure containing various information about a
Tcl command.
.BE
.SH DESCRIPTION
.PP
\fBTcl_CreateObjCommand\fR defines a new command in \fIinterp\fR
and associates it with procedure \fIproc\fR
such that whenever \fIname\fR is
invoked as a Tcl command (e.g., via a call to \fBTcl_EvalObjEx\fR)
the Tcl interpreter will call \fIproc\fR to process the command.
.PP
\fBTcl_CreateObjCommand\fR deletes any existing command
\fIname\fR 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 \fBTcl_GetCommandName\fR.
If \fIname\fR contains any \fB::\fR namespace qualifiers,
then the command is added to the specified namespace;
otherwise the command is added to the global namespace.
If \fBTcl_CreateObjCommand\fR 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.
\fIproc\fR should have arguments and result that match the type
\fBTcl_ObjCmdProc\fR:
.CS
typedef int Tcl_ObjCmdProc(
	ClientData \fIclientData\fR,
	Tcl_Interp *\fIinterp\fR,
	int \fIobjc\fR,
.VS
	Tcl_Obj *CONST \fIobjv\fR[]);
.CE
When \fIproc\fR is invoked, the \fIclientData\fR and \fIinterp\fR parameters
will be copies of the \fIclientData\fR and \fIinterp\fR arguments given to
\fBTcl_CreateObjCommand\fR.  Typically, \fIclientData\fR points to an
application-specific data structure that describes what to do when the
command procedure is invoked. \fIObjc\fR and \fIobjv\fR describe the
arguments to the command, \fIobjc\fR giving the number of argument objects
(including the command name) and \fIobjv\fR giving the values of the
arguments.  The \fIobjv\fR array will contain \fIobjc\fR values, pointing to
the argument objects.  Unlike \fIargv\fR[\fIargv\fR] used in a
string-based command procedure, \fIobjv\fR[\fIobjc\fR] will not contain NULL.
.PP
Additionally, when \fIproc\fR is invoked, it must not modify the contents
of the \fIobjv\fR array by assigning new pointer values to any element of the
array (for example, \fIobjv\fR[\fB2\fR] = \fBNULL\fR) because this will
cause memory to be lost and the runtime stack to be corrupted.  The
\fBCONST\fR in the declaration of \fIobjv\fR 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
\fBTcl_GetIntFromObj\fR on \fIobjv\fR[\fB2\fR] to obtain the integer
representation of that object; that call may change the type of the object
that \fIobjv\fR[\fB2\fR] points at, but will not change where
\fIobjv\fR[\fB2\fR] points.
.VE
.PP
\fIproc\fR must return an integer code that is either \fBTCL_OK\fR,
\fBTCL_ERROR\fR, \fBTCL_RETURN\fR, \fBTCL_BREAK\fR, or \fBTCL_CONTINUE\fR.
See the Tcl overview man page
for details on what these codes mean.  Most normal commands will only
return \fBTCL_OK\fR or \fBTCL_ERROR\fR.
In addition, if \fIproc\fR needs to return a non-empty result,
it can call \fBTcl_SetObjResult\fR to set the interpreter's result.
In the case of a \fBTCL_OK\fR return code this gives the result
of the command,
and in the case of \fBTCL_ERROR\fR this gives an error message.
Before invoking a command procedure,
\fBTcl_EvalObjEx\fR 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.
.PP
The contents of the \fIobjv\fR array belong to Tcl and are not
guaranteed to persist once \fIproc\fR returns: \fIproc\fR should
not modify them.
Call \fBTcl_SetObjResult\fR if you want
to return something from the \fIobjv\fR array.
.PP
Ordinarily, \fBTcl_CreateObjCommand\fR deletes any existing command
\fIname\fR already associated with the interpreter.
However, if the existing command was created by a previous call to
\fBTcl_CreateCommand\fR,
\fBTcl_CreateObjCommand\fR does not delete the command
but instead arranges for the Tcl interpreter to call the
\fBTcl_ObjCmdProc\fR \fIproc\fR in the future.
The old string-based \fBTcl_CmdProc\fR associated with the command
is retained and its address can be obtained by subsequent 
\fBTcl_GetCommandInfo\fR calls. This is done for backwards compatibility.
.PP
\fIDeleteProc\fR will be invoked when (if) \fIname\fR is deleted.
This can occur through a call to \fBTcl_DeleteCommand\fR,
\fBTcl_DeleteCommandFromToken\fR, or \fBTcl_DeleteInterp\fR,
or by replacing \fIname\fR in another call to \fBTcl_CreateObjCommand\fR.
\fIDeleteProc\fR is invoked before the command is deleted, and gives the
application an opportunity to release any structures associated
with the command.  \fIDeleteProc\fR should have arguments and
result that match the type \fBTcl_CmdDeleteProc\fR:
.CS
typedef void Tcl_CmdDeleteProc(ClientData \fIclientData\fR);
.CE
The \fIclientData\fR argument will be the same as the \fIclientData\fR
argument passed to \fBTcl_CreateObjCommand\fR.
.PP
\fBTcl_DeleteCommand\fR deletes a command from a command interpreter.
Once the call completes, attempts to invoke \fIcmdName\fR in
\fIinterp\fR will result in errors.
If \fIcmdName\fR isn't bound as a command in \fIinterp\fR then
\fBTcl_DeleteCommand\fR does nothing and returns -1;  otherwise
it returns 0.
There are no restrictions on \fIcmdName\fR:  it may refer to
a built-in command, an application-specific command, or a Tcl procedure.
If \fIname\fR contains any \fB::\fR namespace qualifiers,
the command is deleted from the specified namespace.
.PP
Given a token returned by \fBTcl_CreateObjCommand\fR,
\fBTcl_DeleteCommandFromToken\fR deletes the command
from a command interpreter.
It will delete a command even if that command has been renamed.
Once the call completes, attempts to invoke the command in
\fIinterp\fR will result in errors.
If the command corresponding to \fItoken\fR
has already been deleted from \fIinterp\fR then
\fBTcl_DeleteCommand\fR does nothing and returns -1;
otherwise it returns 0.
.PP
\fBTcl_GetCommandInfo\fR checks to see whether its \fIcmdName\fR argument
exists as a command in \fIinterp\fR.
\fIcmdName\fR may include \fB::\fR 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 \fBTcl_CmdInfo\fR structure
pointed to by \fIinfoPtr\fR and returns 1.
A \fBTcl_CmdInfo\fR structure has the following fields:
.CS
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;
.CE
The \fIisNativeObjectProc\fR field has the value 1
if \fBTcl_CreateObjCommand\fR was called to register the command;
it is 0 if only \fBTcl_CreateCommand\fR was called.
It allows a program to determine whether it is faster to
call \fIobjProc\fR or \fIproc\fR:
\fIobjProc\fR is normally faster
if \fIisNativeObjectProc\fR has the value 1.
The fields \fIobjProc\fR and \fIobjClientData\fR
have the same meaning as the \fIproc\fR and \fIclientData\fR
arguments to \fBTcl_CreateObjCommand\fR;
they hold information about the object-based command procedure
that the Tcl interpreter calls to implement the command.
The fields \fIproc\fR and \fIclientData\fR
hold information about the string-based command procedure
that implements the command.
If \fBTcl_CreateCommand\fR was called for this command,
this is the procedure passed to it;
otherwise, this is a compatibility procedure
registered by \fBTcl_CreateObjCommand\fR
that simply calls the command's
object-based procedure after converting its string arguments to Tcl objects.
The field \fIdeleteData\fR is the ClientData value
to pass to \fIdeleteProc\fR;  it is normally the same as
\fIclientData\fR but may be set independently using the
\fBTcl_SetCommandInfo\fR procedure.
The field \fInamespacePtr\fR holds a pointer to the
Tcl_Namespace that contains the command.
.PP
\fBTcl_SetCommandInfo\fR is used to modify the procedures and
ClientData values associated with a command.
Its \fIcmdName\fR argument is the name of a command in \fIinterp\fR.
\fIcmdName\fR may include \fB::\fR namespace qualifiers
to identify a command in a particular namespace.
If this command does not exist then \fBTcl_SetCommandInfo\fR returns 0.
Otherwise, it copies the information from \fI*infoPtr\fR 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 \fBTcl_SetCmdInfo\fR will not change a command's namespace;
you must use \fBTcl_RenameCommand\fR to do that.
.PP
\fBTcl_GetCommandName\fR provides a mechanism for tracking commands
that have been renamed.
Given a token returned by \fBTcl_CreateObjCommand\fR
when the command was created, \fBTcl_GetCommandName\fR returns the
string name of the command.  If the command has been renamed since it
was created, then \fBTcl_GetCommandName\fR returns the current name.
This name does not include any \fB::\fR namespace qualifiers.
The command corresponding to \fItoken\fR must not have been deleted.
The string returned by \fBTcl_GetCommandName\fR 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.

.SH "SEE ALSO"
Tcl_CreateCommand, Tcl_ResetResult, Tcl_SetObjResult

.SH KEYWORDS
bind, command, create, delete, namespace, object