report Tcl error that occurred in background processing

## NAME

Tk_BackgroundError - report Tcl error that occurred in background processing

## SYNOPSIS

#include <tk.h>

Tk_BackgroundError(interp)

## ARGUMENTS

`Tcl_Interp *interp` (in)
  Interpreter in which the error occurred.

## DESCRIPTION

This procedure is typically invoked when a Tcl error occurs during ``background processing'' such as executing a Tcl command in response to a button press or menu entry invocation. When such an error occurs, the error condition is reported to Tk or to a widget or some other C code, and there is not usually any obvious way for that code to report the error to the user. In these cases the code calls Tk_BackgroundError with an interp argument identifying the interpreter in which the error occurred. Tk_BackgroundError attempts to invoke the tkerror Tcl command to report the error in an application-specific fashion. If no tkerror command exists, or if it returns with an error condition, then Tk_BackgroundError reports the error itself by printing a message on the standard error file.

Tk_BackgroundError does not invoke tkerror immediately (in some cases this could interfere with scripts that are in process at the time the error occurred). Instead, it invokes tkerror later as an idle callback. Tk_BackgroundError saves the values of the errorInfo and errorCode variables and restores these values just before invoking tkerror.

It is possible for many background errors to accumulate before tkerror is invoked. When this happens, each of the errors is processed in order. However, if tkerror returns a break exception, then all remaining error reports for the interpreter are skipped.

## KEYWORDS

background, error, tkerror