Tcl_CreateCommand(3tcl) Tcl Library Procedures Tcl_CreateCommand(3tcl)
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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 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
interpreter; allows for
command-specific cleanup.
If NULL, then no procedure
is called before the com-
mand 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 com-
mand (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_Create-
Command for backwards compatibility.
The procedures Tcl_DeleteCommand, Tcl_GetCommandInfo, and Tcl_SetCom-
mandInfo 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_GetCommand-
Name. If cmdName contains any :: namespace qualifiers, then the com-
mand 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_CreateCom-
mand. Typically, clientData points to an application-specific data
structure that describes what to do when the command procedure is in-
voked. Argc and argv describe the arguments to the command, argc giv-
ing the number of arguments (including the command name) and argv giv-
ing the values of the arguments as strings. The argv array will con-
tain 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 over-
view man page for details on what these codes mean. Most normal com-
mands 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 er-
ror message. The Tcl_SetResult procedure provides an easy interface
for setting the return value; for complete details on how the inter-
preter 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 some-
thing 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 replac-
ing cmdName in another call to Tcl_CreateCommand. DeleteProc is in-
voked before the command is deleted, and gives the application an op-
portunity 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_Set-
CommandInfo, Tcl_GetCommandName, Tcl_SetObjResult
KEYWORDS
bind, command, create, delete, interpreter, namespace
Tcl Tcl_CreateCommand(3tcl)
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