Tcl_AppInit manual page - Tcl Library Procedures

## Tcl8.6.4 Documentation > Tcl C API, version 8.6.4 > AppInit

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  NAME
    Tcl_AppInit — perform application-specific initialization
  SYNOPSIS
    #include <tcl.h>
    int
    Tcl_AppInit(interp)
  ARGUMENTS
  DESCRIPTION
  SEE ALSO
  KEYWORDS

### NAME

Tcl_AppInit — perform application-specific initialization

### SYNOPSIS

#include <tcl.h>
int
Tcl_AppInit(interp)

### ARGUMENTS

Tcl_Interp *interp (in)
  Interpreter for the application.

### DESCRIPTION

Tcl_AppInit is a “hook” procedure that is invoked by the main programs for Tcl applications such as tclsh and wish. 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 Tcl_AppInit to replace the default version provided by Tcl, then link your new Tcl_AppInit with the Tcl library.

Tcl_AppInit is invoked by Tcl_Main and Tk_Main after their own initialization and before entering the main loop to process commands. Here are some examples of things that Tcl_AppInit might do:

1. Call initialization procedures for various packages used by the application. Each initialization procedure adds new commands to interp for its package and performs other package-specific initialization.

2. Process command-line arguments, which can be accessed from the Tcl variables argv and argv0 in interp.

3. Invoke a startup script to initialize the application.

4. Use the routines Tcl_SetStartupScript and Tcl_GetStartupScript to set or query the file and encoding that the active Tcl_Main or Tk_Main routine will use as a startup script.

Tcl_AppInit returns TCL_OK or TCL_ERROR. If it returns TCL_ERROR then it must leave an error message in for the interpreter's result; otherwise the result is ignored.

In addition to Tcl_AppInit, your application should also contain a procedure main that calls Tcl_Main as follows:

    Tcl_Main(argc, argv, Tcl_AppInit);

The third argument to Tcl_Main gives the address of the application-specific initialization procedure to invoke. This means that you do not have to use the name Tcl_AppInit for the procedure, but in practice the name is nearly always Tcl_AppInit (in versions before Tcl 7.4 the name Tcl_AppInit 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 tclAppInit.c from the Tcl library or source directory. It already contains a main procedure and a template for Tcl_AppInit that you can modify for your application.

### SEE ALSO

Tcl_Main

### KEYWORDS

application, argument, command, initialization, interpreter
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