Tcl\_AppInit(3) Tcl Library Procedures Tcl\_AppInit(3)

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```

# [NAME](#NAME)

Tcl\_AppInit - perform application-specific initialization

# [SYNOPSIS](#SYNOPSIS)

```
#include <tcl.h>

int
Tcl_AppInit(interp)
```

# [ARGUMENTS](#ARGUMENTS)

Tcl\_Interp *\*interp* (in)

Interpreter for the application.

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```

# [DESCRIPTION](#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](#SEE_ALSO)

[Tcl\_Main(3)](/man/os/tcl/Tcl_Main.3)

# [KEYWORDS](#KEYWORDS)

application, argument, command, initialization, interpreter

7.0 Tcl

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Document: Tcl_AppInit(3) from tcl 9.1.0-r2 (Chainguard OS)
Source: https://downloads.sourceforge.net/project/tcl/Tcl/9.1.0/tcl9.1.0-src.tar.gz