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 elements in argv.
char *argv[] (in) Array of strings containing command-line arguments.
Tcl_AppInitProc *appInitProc (in) Address of an application-specific initialization proce-dure. procedure.
dure. 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 ini-tialization initialization
tialization 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 sys-tems. systems.
tems. 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 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 initial-ize initialize
ize 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 interac-tive interactive
tive 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 argument. This procedure provides a ``hook'' for the application
to perform its own initialization of the interpreter created by Tcl_Main, such as defining applica-tion-specific application-specific
tion-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 variable 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 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 output 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 interac- |
tive 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 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 program
Tcl 8.4 Tcl_Main(3)
|