tcl_createcommand(3)

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) Inter

preter in
which to
create new
command.

CONST char *cmd_
Name (in)

Name of
command.

Tcl_CmdProc *proc (in) Implemen

tation of
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
cmdName is deleted
from the
inter
preter;
allows for
commandspecific
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 cmd_ Name 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 stringbased 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 rep
resentation that can be manipulated more efficiently.
Also, Tcl's interpreter now uses objects internally. In
order to invoke a string-based command procedure regis
tered 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 com
mands 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_Cre ateCommand.

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 giv ing 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.

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, 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
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 opportu
nity to release any structures associated with the com
mand. 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_GetCommand
Info, Tcl_SetCommandInfo, Tcl_GetCommandName, Tcl_SetOb
jResult

KEYWORDS

bind, command, create, delete, interpreter, namespace

Tcl Tcl_CreateCommand(3)