signal(3f)

Name
signal - changes the action for a signal

Syntax
integer ret, signum, flag
external signal, proc
ret = signal ( signum, proc, flag )

Description
When a process incurs a signal ( see signal(3) ), the default action is usually to clean up and abort. A user can choose to write an alternative signal handling routine with a call to signal.

The signum argument is the signal number ( see signal(3) ). If the specified flag is negative, then proc must be the name of the user signal handling routine. If flag is zero or positive, then proc is ignored and the value of 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 flag have specific meanings: zero means "use the default action", one means "ignore this signal".

Restrictions
The f77 compiler arranges to trap certain signals when a process is started. The only way to restore the default f77 action is to save the returned value from the first call to signal.

If the user signal handler is called, it is passed the signal number as an integer argument.

Return Values
A positive return value is the previous action definition. A value greater than one is the address of a routine that is to be called on occurrence of the given signal. The returned value can be used in subsequent calls to signal in order to restore a previous action definition. A negative return value is the negation of a system error code.

Files
libU77.a

See Also
kill(1), signal(3), kill(3f)