signal.3f

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)signal.3f	8.1	9/11/90
.TH signal 3f VAX "" Unsupported
.SH Name
signal \- change the action for a signal
.SH Syntax
.B integer function signal(signum, proc, flag)
.br
.B integer signum, flag
.br
.B external proc
.SH Description
.NXR "signal subroutine (FORTRAN)"
.NXR "signal" "changing action"
When a process incurs a signal, 
the default action
is usually to clean up and abort.
For further information, see 
.MS signal 3 .
The user may choose to write an alternative signal handling routine.
A call to
.PN signal
is the way this alternate action is specified to the system.
.PP
The
.I signum
is the signal number.  For further information, see 
.MS signal 3 .
If
.I flag
is negative, then
.I proc
must be the name of the user signal handling routine.
If
.I flag
is zero or positive, then
.I proc
is ignored and the value of
.I flag
is passed to the system as the signal action definition.
In particular, this is how previously saved signal actions can
be restored.
Two possible values for
.I flag
have specific meanings:
0 means "use the default action" (See Note),
1 means "ignore this signal".
.PP
A positive returned value is the previous action definition.
A value greater than 1 is the address of a routine that
was to have been called on occurrence of the given signal.
The returned value can be used in subsequent calls to
.PN signal
in order to restore a previous action definition.
A negative returned value is the negation of a system error code.
For further information, see 
.MS perror 3f .
.NT
The
.PN f77
arranges to trap certain signals when a process is started.
The only way to restore the default
.PN f77
action is to save the returned
value from the first call to
.PN signal .
.PP
If the user signal handler is called,
it will be passed the signal number
as an integer argument.
.NE
.SH Files
.ie \nM /usr/ucb/lib/libU77.a
.el /usr/lib/libU77.a
.SH See Also
kill(1), kill(3f), signal(3)