Tcl_CreateCommand(3) Tcl Library Procedures Tcl_CreateCommand(3)

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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.
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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 values.
The value-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 values as arguments and those values can retain an internal
representation that can be manipulated more efficiently. Also, Tcl's
interpreter now uses values 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 value
before the call. 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; 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

Tcl Tcl_CreateCommand(3)