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Tcl_Main(3)		    Tcl	Library	Procedures		   Tcl_Main(3)

______________________________________________________________________________

NAME
       Tcl_Main,  Tcl_MainEx,  Tcl_MainExW, Tcl_SetStartupScript, Tcl_GetStar-
       tupScript, Tcl_SetMainLoop - main program, startup  script,  and	 event
       loop definition for Tcl-based applications

SYNOPSIS
       #include	<tcl.h>

       Tcl_Main(argc, argv, appInitProc)

       Tcl_MainEx(argc,	charargv, appInitProc, interp)

       Tcl_MainExW(argc, wideargv, appInitProc,	interp)

       Tcl_SetStartupScript(path, encoding)

       Tcl_Obj *
       Tcl_GetStartupScript(encodingPtr)

       Tcl_SetMainLoop(mainLoopProc)

ARGUMENTS
       Tcl_Size	argc (in)			    Number   of	  elements  in
						    argv.

       char *argv[] (in)			    Array of strings  contain-
						    ing	  command-line	 argu-
						    ments.  On	Windows,  when
						    using -DUNICODE, the para-
						    meter   type   changes  to
						    wchar_t *.

       char *charargv[]	(in)			    As	argv,  but  does   not
						    change type	to wchar_t.

       char *wideargv[]	(in)			    As	argv,  but type	is al-
						    ways wchar_t.

       Tcl_AppInitProc *appInitProc (in)	    Address of an application-
						    specific	initialization
						    procedure.	 The value for
						    this argument  is  usually
						    Tcl_AppInit.

       Tcl_Obj *path (in)			    Name  of  file  to	use as
						    startup script, or NULL.

       const char *encoding (in)		    Encoding of	file to	use as
						    startup script, or NULL.

       const char **encodingPtr	(out)		    If non-NULL,  location  to
						    write a copy of the	(const
						    char  *)  pointing	to the
						    encoding name.

       Tcl_MainLoopProc	*mainLoopProc (in)	    Address of an application-
						    specific event loop	proce-
						    dure.

       Tcl_Interp *interp (in)			    Already created Tcl	Inter-
						    preter.
______________________________________________________________________________

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 sup-
       ports both interactive interpretation of	Tcl and	evaluation of a	script
       contained  in a file given as a command line argument.  Tcl_Main	is of-
       fered 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 li-
       brary.  If the standard Tcl library is a	dll (so, not a static .lib/.a)
       , then the program must be linked against the stub library as well. Ex-
       tensions	(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 main
       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  whether  the
       filename	 and  encoding	of a startup script has	been established.  The
       routines	Tcl_SetStartupScript and Tcl_GetStartupScript  are  the	 tools
       for controlling this configuration of Tcl_Main.

       Tcl_SetStartupScript  registers	the value path as the name of the file
       for Tcl_Main to evaluate	as its startup script.	The value encoding  is
       Tcl's  name  for	 the  encoding used to store the text in that file.  A
       value of	NULL for encoding is a signal to use the system	 encoding.   A
       value  of  NULL	for  path  erases  any	existing  registration so that
       Tcl_Main	will not evaluate any startup script.

       Tcl_GetStartupScript queries the	registered file	name and encoding  set
       by  the	most recent Tcl_SetStartupScript call in the same thread.  The
       stored file name	is returned, and the stored encoding name  is  written
       to space	pointed	to by encodingPtr, when	that is	not NULL.

       The  file name and encoding values managed by the routines Tcl_SetStar-
       tupScript and Tcl_GetStartupScript are stored per-thread.  Although the
       storage and retrieval functions of these	routines work in  any  thread,
       only  those  calls in the same main thread as Tcl_Main can have any in-
       fluence on it.

       The caller of Tcl_Main may call Tcl_SetStartupScript first to establish
       its desired startup script.  If Tcl_Main	finds  that  no	 such  startup
       script  has  been  established,	it consults the	first few arguments in
       argv.  If they 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.	 Tcl_Main  then	 calls
       Tcl_SetStartupScript with these values.

       Tcl_Main	 then  defines in its main 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  perform
       its  own	initialization of the interpreter created by Tcl_Main, such as
       defining	application-specific commands.	The application	initialization
       routine might also call Tcl_SetStartupScript to (re-)set	the  file  and
       encoding	 to  be	 used as a startup script.  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  calls  Tcl_GetStartupScript
       to  determine  what  startup  script  has been requested, if any.  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 main interpreter.	If that	 variable  exists  and
       holds the name of a readable file, the contents of that file are	evalu-
       ated  in	the main 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 main 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) re-
       turns, Tcl_Main will also evaluate the exit command.

       Tcl_Main	can not	be used	in stub-enabled	extensions.

       The difference between Tcl_MainEx and Tcl_MainExW is that the arguments
       are passed as characters	or wide	characters. When used in  stub-enabled
       embedders,  the	stubs  table  must  be	first initialized using	one of
       Tcl_InitSubsystems,     Tcl_SetPanicProc,     Tcl_FindExecutable	    or
       TclZipfs_AppHook.

REFERENCE COUNT	MANAGEMENT
       Tcl_SetStartupScript takes a value (or NULL) for	its path argument, and
       will increment the reference count of it.

       Tcl_GetStartupScript  returns  a	value with reference count at least 1,
       or NULL.	It's encodingPtr is also used (if non-NULL) to return a	 value
       with a reference	count at least 1, or NULL. In both cases, the owner of
       the values is the current thread.

SEE ALSO
       tclsh(1),    Tcl_GetStdChannel(3),   Tcl_StandardChannels(3),   Tcl_Ap-
       pInit(3), exit(n), encoding(n)

KEYWORDS
       application-specific initialization, command-line arguments, main  pro-
       gram

Tcl				      9.0			   Tcl_Main(3)

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