bgerror(n)						       Tcl Built-In Commands							bgerror(n)

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NAME

       bgerror - Command invoked to process background errors

SYNOPSIS

       bgerror message
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DESCRIPTION

       The bgerror command doesn't exist as built-in part of Tcl.  Instead, individual applications or users can define a bgerror command (e.g. as
       a Tcl procedure) if they wish to handle background errors.

       A background error is one that occurs in an event handler or some other command that didn't originate with the application.   For  example,
       if  an error occurs while executing a command specified with the after command, then it is a background error.  For a non-background error,
       the error can simply be returned up through nested Tcl command evaluations 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 Tcl library and
       there is no obvious way for Tcl to report the error.

       When Tcl detects a background error, it saves information about the error and invokes the bgerror command later as an idle  event  handler.
       Before invoking bgerror, Tcl restores the errorInfo and errorCode variables to their values at the time the error occurred, then it invokes
       bgerror with the error message as its only argument.  Tcl assumes that the application has implemented the bgerror command,  and  that  the
       command will report the error in a way that makes sense for the application.  Tcl will ignore any result returned by the bgerror command as
       long as no error is generated.

       If another Tcl error occurs within the bgerror command (for example, because no bgerror command has been  defined)  then  Tcl  reports  the
       error itself by writing a message to stderr.

       If  several  background	errors	accumulate  before bgerror is invoked to process them, bgerror will be invoked once for each error, in the
       order they occurred.  However, if bgerror returns with a break exception, then any remaining errors are skipped without calling bgerror.

       Tcl has no default implementation for bgerror. However, in applications using Tk there is a default bgerror procedure which posts a  dialog
       box containing the error message and offers the user a chance to see a stack trace showing where the error occurred.  In addition to allow-
       ing the user to view the stack trace, the dialog provides an additional application configurable button which may be used, for example,	to
       save  the  stack trace to a file.  By default, this is the behavior associated with that button.  This behavior can be redefined by setting
       the option database values *ErrorDialog.function.text, to specify the caption for the function button,  and  *ErrorDialog.function.command,
       to specify the command to be run.  The text of the stack trace is appended to the command when it is evaluated.	If either of these options
       is set to the empty string, then the additional button will not be displayed in the dialog.

SEE ALSO

       after(n), tclvars(n)

KEYWORDS

       background error, reporting

Tcl									7.5								bgerror(n)