Tcl_Main

Tcl_Main(3)                 Tcl Library Procedures                 Tcl_Main(3)



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NAME
       Tcl_Main, Tcl_SetStartupScript, Tcl_GetStartupScript, Tcl_SetMainLoop -
       main program, startup script, and event loop definition for Tcl-based
       applications

SYNOPSIS
       #include <tcl.h>

       Tcl_Main(argc, argv, appInitProc)

       Tcl_SetStartupScript(path, encoding)

       Tcl_Obj *
       Tcl_GetStartupScript(encodingPtr)

       Tcl_SetMainLoop(mainLoopProc)

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

       char *argv[] (in)                            Array of strings
                                                    containing command-line
                                                    arguments. On Windows,
                                                    when using -DUNICODE, the
                                                    parameter type changes to
                                                    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
                                                    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 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_SetStartupScript 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 master thread as Tcl_Main can
       have any influence 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 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 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 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(3), Tcl_StandardChannels(3),
       Tcl_AppInit(3), exit(n), encoding(n)

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



Tcl                                   8.4                          Tcl_Main(3)