DEL

Section: C Library Functions (3)
Updated: 12/6/79
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NAME

del - interrupt handling package

SYNOPSIS

#include <del.h>

ENABLEDEL;
IGNOREDEL;
DISABLEDEL;

DELBREAK;
DELRETURN;
DELRETN(value);
DELCLEAR;

DESCRIPTION

Del is a small subroutine used as an interrupt trap routine. It is used with the macro package <del.h> to provide a complete facility for trapping interrupts (DEL or RUBOUT key on the terminal).

The macro file incldes all the definitions listed above, and uses an external int (_del_) as an interrupt flag. When an interrupt occurs, the del subroutine will increment _del_ (usually from 0 to 1), signal(2) itself for further interrupts, and return. The user may then test this variable with the macros listed above.

These macros control overall interrupt handling:

ENABLEDEL: clears _del_ and begins interrupt trapping.
IGNOREDEL: clears _del_ and ignores interrupts.
DISABLEDEL: clears _del_ and restores normal interrupt handling (kill process on interrupt).

These macros allow you to see if an interrupt has occurred (they do nothing if none has occurred):

DELBREAK: clears _del_ and acts like a break statement.
DELRETURN: clears _del_ and acts like a return statement.
DELRETN(value): clears _del_ and acts like the statement return(value).
DELCLEAR: clears _del_ and prints "Break ignored".

In addition, you may perform a simpler test for interrupts like this:

        if (_del_) ...

This is useful in conjunction with the above macros when you wish, for example, to exit from several layers of loops or procedures.

FILES

/usr/cs/include/del.h -- macro package

DIAGNOSTICS

Break!: printed by DELBREAK, DELRETURN, and DELRETURN(value) if an interrupt has occurred.
Break ignored.: printed by DELCLEAR if an interrupt has occurred.

BUGS

It is possible, in any UNIX program which traps interrupts, for an interrupt to be missed if it immediately follows a previous interrupt of the same kind.

This document was created by man2html, using the manual pages.
Time: 12:50:46 GMT, May 26, 2025

DEL