NAME¶
Tcl_CreateCommand - implement new commands in C
SYNOPSIS¶
#include <tcl.h>
Tcl_Command
Tcl_CreateCommand(interp, cmdName, proc, clientData, deleteProc)
ARGUMENTS¶
- 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
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.
DESCRIPTION¶
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 objects. The object-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 objects as arguments and those objects can retain an
internal representation that can be manipulated more efficiently. Also, Tcl's
interpreter now uses objects 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 object before the call and
create a new Tcl object to hold the string result returned by the string-based
command procedure. 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(
ClientData clientData,
Tcl_Interp * interp,
int argc,
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 to
point to a string value; 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
Tcl_CmdDeleteProc:
typedef void Tcl_CmdDeleteProc(
ClientData clientData);
The
clientData argument will be the same as the
clientData
argument passed to
Tcl_CreateCommand.
SEE ALSO¶
Tcl_CreateObjCommand, Tcl_DeleteCommand, Tcl_GetCommandInfo, Tcl_SetCommandInfo,
Tcl_GetCommandName, Tcl_SetObjResult
KEYWORDS¶
bind, command, create, delete, interpreter, namespace