Error(3) User Contributed Perl Documentation Error(3)

# [NAME](#NAME)

Tk::Error - Method invoked to process background errors

# [SYNOPSIS](#SYNOPSIS)

Customization:

```
    require Tk::ErrorDialog;
```

or

```
    sub Tk::Error
    {
      my ($widget,$error,@locations) = @_;
      ...
    }
```

# [DESCRIPTION](#DESCRIPTION)

The **Tk::Error** method is invoked by perl/Tk when a background error occurs. Two possible implementations are provided in the distribution and individual applications or users can (re)define a **Tk::Error** method (e.g. as a perl sub) if they wish to handle background errors in some other manner.

A background error is one that occurs in a command that didn't originate with the application. For example, if an error occurs while executing a callback specified with a bind or a after command, then it is a background error. For a non-background error, the error can simply be returned up through nested subroutines until it reaches the top-level code in the application; then the application can report the error in whatever way it wishes. When a background error occurs, the unwinding ends in the Tk library and there is no obvious way for Tk to report the error.

When Tk detects a background error, it saves information about the error and invokes the **Tk::Error** method later when Tk is idle.

**Tk::Error** is invoked by perl/Tk as if by the perl code:

    *$mainwindow*->**Tk::Error**(*"error message"*, *location ...*);

*$mainwindow* is the **MainWindow** associated with widget which detected the error, *"error message"* is a string describing the error that has been detected, *location* is a list of one or more "locations" which describe the call sequence at the point the error was detected.

The locations are a typically a mixture of perl location reports giving script name and line number, and simple strings describing locations in core Tk or perl/Tk C code.

Tk will ignore any result returned by the **Tk::Error** method. If another error occurs within the **Tk::Error** method (for example if it calls **die**) then Tk reports this error itself by writing a message to stderr (this is to avoid infinite loops due to any bugs in **Tk::Error**).

If several background errors accumulate before **Tk::Error** is invoked to process them, **Tk::Error** will be invoked once for each error, in the order they occurred. However, if **Tk::Error** calls **Tk->break**, then any remaining errors are skipped without calling **Tk::Error**.

The **Tk** module includes a default **Tk::Error** subroutine that simply reports the error on stderr.

# [Tk::ErrorDialog](#Tk::ErrorDialog)

An alternate definition is provided via:

    "require Tk::ErrorDialog;"

that posts a dialog box containing the error message and offers the user a chance to see a stack trace showing where the error occurred.

This is an OO implementation of the Tcl/Tk command **bgerror**, with a twist: since there is only one **ErrorDialog** widget, you aren't required to invoke the constructor to create it; it will be created automatically when the first background error occurs. However, in order to configure the *-cleanupcode* and *-appendtraceback* **ErrorDialog** options you must call the constructor and create it manually.

The **ErrorDialog** object essentially consists of two subwidgets: a **Dialog** widget to display the background error and a **Text** widget for the traceback information. If required, you can invoke various widget methods to customize these subwidgets - their advertised names are described below.

    *$mw*->**ErrorDialog**(-cleanupcode => *code*, -appendtraceback => *bool*);

$mw is a window reference.

*code* is a CODE reference if special post-background error processing is required (default is undefined). The callback subroutine is called with @_ having the same arguments that **Tk::Error** was invoked with.

*bool* is a boolean indicating whether or not to append successive tracebacks (default is 1, do append).

## [Advertised ErrorDialog widgets](#Advertised_ErrorDialog_widgets)

*error\_dialog* is the Dialog widget reference.

*text* is the Text widget reference containing the traceback information.

# [BUGS](#BUGS)

If **after** or **fileevent** are not invoked as methods of a widget then perl/Tk is unable to provide a *$mainwindow* argument. To support such code from earlier versions of perl/Tk perl/Tk therefore calls **Tk::Error** with string 'Tk' instead: **Tk->Tk::Error\\(...\\)**. In this case the **Tk::Error** in **Tk::ErrorDialog** and similar implementations cannot "popup" a window as they don't know which display to use. A mechanism to supply *the* **MainWindow** in applications which only have one (a very common case) should be provided.

# [SEE ALSO](#SEE_ALSO)

Tk::bind Tk::after Tk::fileevent

# [KEYWORDS](#KEYWORDS)

background error, reporting

2026-10-25 perl v5.44.0

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Document: Tk::Error(3pm) from perl-tk 804.036-r12 (Chainguard OS)
Source: https://github.com/eserte/perl-tk