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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 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 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, argv_,
       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 applicationspecific
       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 interactive
       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)