Provided by: tcl8.4-doc_8.4.19-4ubuntu3_all bug

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 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.

       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  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
       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 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
       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 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
       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(3tcl),    Tcl_StandardChannels(3tcl),    Tcl_AppInit(3tcl),
       exit(3tcl)

KEYWORDS

       application-specific initialization, command-line arguments, main program