Tcl_Main(3)
Tcl_Main(3) Tcl Library Procedures Tcl_Main(3)
_________________________________________________________________
NAME
Tcl_Main, Tcl_SetMainLoop - main program and event loop
definition for Tcl-based applications
SYNOPSIS
#include <tcl.h>
Tcl_Main(argc, argv, appInitProc)
Tcl_SetMainLoop(mainLoopProc)
ARGUMENTS
int argc (in) Number of ele-
ments in argv.
char *argv[] (in) Array of
strings con-
taining
command-line
arguments.
Tcl_AppInitProc *appInitProc (in) Address of an
application-
specific ini-
tialization
procedure. The
value for this
argument is
usually
Tcl_AppInit.
Tcl_MainLoopProc *mainLoopProc (in) Address of an
application-
specific event
loop procedure.
_________________________________________________________________
DESCRIPTION
Tcl_Main can serve as the main program for Tcl-based shell
applications. A "shell application" is a program like tclsh
or wish that supports both interactive interpretation of Tcl
and evaluation of a script contained in a file given as a
command line argument. Tcl_Main is offered as a convenience
to developers of shell applications, so they do not have to
reproduce all of the code for proper initialization of the
Tcl library and interactive shell operation. Other styles
of embedding Tcl in an application are not supported by
Tcl_Main. Those must be achieved by calling lower level
functions in the Tcl library directly.
Tcl Last change: 8.4 1
Tcl_Main(3) Tcl Library Procedures Tcl_Main(3)
The Tcl_Main function has been offered by the Tcl library
since release Tcl 7.4. In older releases of Tcl, the Tcl
library itself defined a function main, but that lacks flex-
ibility of embedding style and having a function main in a
library (particularly a shared library) causes problems on
many systems. Having main in the Tcl library would also
make it hard to use Tcl in C++ programs, since C++ programs
must have special C++ main functions.
Normally each shell application contains a small main func-
tion that does nothing but invoke Tcl_Main. Tcl_Main then
does all the work of creating and running a tclsh-like
application.
Tcl_Main is not provided by the public interface of Tcl's
stub library. Programs that call Tcl_Main must be linked
against the standard Tcl library. Extensions (stub-enabled
or not) are not intended to call Tcl_Main.
Tcl_Main is not thread-safe. It should only be called by a
single master thread of a multi-threaded application. This
restriction is not a problem with normal use described
above.
Tcl_Main and therefore all applications based upon it, like
tclsh, use Tcl_GetStdChannel to initialize the standard
channels to their default values. See Tcl_StandardChannels
for more information.
Tcl_Main supports two modes of operation, depending on the
values of argc and argv. If the first few arguments in argv
match ?-encoding name? fileName, where fileName does not
begin with the character -, then fileName is taken to be the
name of a file containing a startup script, and name is
taken to be the name of the encoding of the contents of that
file, which Tcl_Main will attempt to evaluate. Otherwise,
Tcl_Main will enter an interactive mode.
In either mode, Tcl_Main will define in its master inter-
preter the Tcl variables argc, argv, argv0, and
tcl_interactive, as described in the documentation for
tclsh.
When it has finished its own initialization, but before it
processes commands, Tcl_Main calls the procedure given by
the appInitProc argument. This procedure provides a "hook"
for the application to perform its own initialization of the
interpreter created by Tcl_Main, such as defining
application-specific commands. The procedure must have an
interface that matches the type Tcl_AppInitProc:
typedef int Tcl_AppInitProc(Tcl_Interp *interp);
Tcl Last change: 8.4 2
Tcl_Main(3) Tcl Library Procedures Tcl_Main(3)
AppInitProc is almost always a pointer to Tcl_AppInit; for
more details on this procedure, see the documentation for
Tcl_AppInit.
When the appInitProc is finished, Tcl_Main enters one of its
two modes. If a startup script has been provided, Tcl_Main
attempts to evaluate it. Otherwise, interactive mode begins
with examination of the variable tcl_rcFileName in the mas-
ter interpreter. If that variable exists and holds the name
of a readable file, the contents of that file are evaluated
in the master interpreter. Then interactive operations
begin, with prompts and command evaluation results written
to the standard output channel, and commands read from the
standard input channel and then evaluated. The prompts
written to the standard output channel may be customized by
defining the Tcl variables tcl_prompt1 and tcl_prompt2 as
described in the documentation for tclsh. The prompts and
command evaluation results are written to the standard out-
put channel only if the Tcl variable tcl_interactive in the
master interpreter holds a non-zero integer value.
Tcl_SetMainLoop allows setting an event loop procedure to be
run. This allows, for example, Tk to be dynamically loaded
and set its event loop. The event loop will run following
the startup script. If you are in interactive mode, setting
the main loop procedure will cause the prompt to become
fileevent based and then the loop procedure is called. When
the loop procedure returns in interactive mode, interactive
operation will continue. The main loop procedure must have
an interface that matches the type Tcl_MainLoopProc:
typedef void Tcl_MainLoopProc(void);
Tcl_Main does not return. Normally a program based on
Tcl_Main will terminate when the exit command is evaluated.
In interactive mode, if an EOF or channel error is encoun-
tered on the standard input channel, then Tcl_Main itself
will evaluate the exit command after the main loop procedure
(if any) returns. In non-interactive mode, after Tcl_Main
evaluates the startup script, and the main loop procedure
(if any) returns, Tcl_Main will also evaluate the exit com-
mand.
SEE ALSO
tclsh(1), Tcl_GetStdChannel(3), Tcl_StandardChannels(3),
Tcl_AppInit(3), exit(n)
KEYWORDS
application-specific initialization, command-line arguments,
main program
Tcl Last change: 8.4 3
Man(1) output converted with
man2html