path: root/doc/AppInit.3

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'\" RCS: @(#) $Id: AppInit.3,v 1.5 2006/07/30 16:18:59 jenglish Exp $
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.so man.macros
.TH Tcl_AppInit 3 7.0 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_AppInit \- perform application-specific initialization
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
int
\fBTcl_AppInit\fR(\fIinterp\fR)
.SH ARGUMENTS
.AS Tcl_Interp *interp
.AP Tcl_Interp *interp in
Interpreter for the application.
.BE

.SH DESCRIPTION
.PP
\fBTcl_AppInit\fR is a ``hook'' procedure that is invoked by
the main programs for Tcl applications such as \fBtclsh\fR and \fBwish\fR.
Its purpose is to allow new Tcl applications to be created without
modifying the main programs provided as part of Tcl and Tk.
To create a new application you write a new version of
\fBTcl_AppInit\fR to replace the default version provided by Tcl,
then link your new \fBTcl_AppInit\fR with the Tcl library.
.PP
\fBTcl_AppInit\fR is invoked by \fBTcl_Main\fR and \fBTk_Main\fR
after their own initialization and before entering the main loop
to process commands.
Here are some examples of things that \fBTcl_AppInit\fR might do:
.IP [1]
Call initialization procedures for various packages used by
the application.
Each initialization procedure adds new commands to \fIinterp\fR
for its package and performs other package-specific initialization.
.IP [2]
Process command-line arguments, which can be accessed from the
Tcl variables \fBargv\fR and \fBargv0\fR in \fIinterp\fR.
.IP [3]
Invoke a startup script to initialize the application.
.LP
\fBTcl_AppInit\fR returns \fBTCL_OK\fR or \fBTCL_ERROR\fR.
If it returns \fBTCL_ERROR\fR then it must leave an error message in
for the interpreter's result;  otherwise the result is ignored.
.PP
In addition to \fBTcl_AppInit\fR, your application should also contain
a procedure \fBmain\fR that calls \fBTcl_Main\fR as follows:
.CS
Tcl_Main(argc, argv, Tcl_AppInit);
.CE
The third argument to \fBTcl_Main\fR gives the address of the
application-specific initialization procedure to invoke.
This means that you don't have to use the name \fBTcl_AppInit\fR
for the procedure, but in practice the name is nearly always
\fBTcl_AppInit\fR (in versions before Tcl 7.4 the name \fBTcl_AppInit\fR
was implicit;  there was no way to specify the procedure explicitly).
The best way to get started is to make a copy of the file
\fBtclAppInit.c\fR from the Tcl library or source directory.
It already contains a \fBmain\fR procedure and a template for
\fBTcl_AppInit\fR that you can modify for your application.

.SH KEYWORDS
application, argument, command, initialization, interpreter