Tcl_Main(3tcl)
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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 elements in argv.
char *argv[] (in) Array of strings containing
command-line arguments.
Tcl_AppInitProc *appInitProc (in) Address of an application-
specific initialization pro-
cedure. The value for this
argument is usually
Tcl_AppInit.
Tcl_MainLoopProc *mainLoopProc (in) Address of an application-
specific event loop proce-
dure.
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DESCRIPTION
Tcl_Main can serve as the main program for Tcl-based shell applica-
tions. 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.
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 flexibility 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 function 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 mas-
ter 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 argv[1] exists and does not begin with the character
-, it is taken to be the name of a file containing a startup script,
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 interpreter 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 argu-
ment. This procedure provides a ``hook'' for the application to per-
form 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);
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 vari-
able tcl_rcFileName in the master 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 stan-
dard 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 output chan-
nel 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 opera- |
tion 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 encountered 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 command.
SEE ALSO
tclsh(1), Tcl_GetStdChannel(3), Tcl_StandardChannels(3),
Tcl_AppInit(3), exit(n)
KEYWORDS
application-specific initialization, command-line arguments, main pro-
gram
Tcl 8.4 Tcl_Main(3)
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