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Tcl_Main(3)			      Tcl Library Procedures			      Tcl_Main(3)

_________________________________________________________________________________________________

NAME
       Tcl_Main,  Tcl_SetMainLoop - main program and event loop definition for Tcl-based applica-
       tions

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 initial-
						    ization procedure.	The value for this  argu-
						    ment 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  appli-
       cation"	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  inter-
       active 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	flexibil-
       ity  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 func-
       tions.

       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  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 interac-
       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  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 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 eval-
       uated in the master interpreter.  Then interactive operations begin, with prompts and com-
       mand 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 exam-
       ple, Tk to be dynamically loaded and set its event loop.  The event loop will run  follow-
       ing  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 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 evalu-
       ates 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)
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