Tcl_Main(3)                                                   Tcl Library Procedures                                                   Tcl_Main(3)

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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 procedure.  The value for this argument is
                                                    usually Tcl_AppInit.

       Tcl_MainLoopProc *mainLoopProc (in)          Address of an application-specific event loop procedure.
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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  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
       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 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 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 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 evalu-
       ate 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 opera-
       tions 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, interac-
       tive 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)