Provided by: tcl8.6-doc_8.6.10+dfsg-1_all 
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(3tcl), Tcl_StandardChannels(3tcl), Tcl_AppInit(3tcl), exit(3tcl),
encoding(3tcl)
KEYWORDS
application-specific initialization, command-line arguments, main program
Tcl 8.4 Tcl_Main(3tcl)