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Test Your Knowledge in Computers #484
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A compiler transforms source code into object code, a floating point number format that machines understand.
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signal(3f) [bsd man page]

SIGNAL(3F)																SIGNAL(3F)

NAME
signal - change the action for a signal SYNOPSIS
integer function signal(signum, proc, flag) integer signum, flag external proc DESCRIPTION
When a process incurs a signal (see signal(3C)) the default action is usually to clean up and abort. The user may choose to write an alternative signal handling routine. A call to signal is the way this alternate action is specified to the system. Signum is the signal number (see signal(3C)). If 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 particu- lar, this is how previously saved signal actions can be restored. Two possible values for flag have specific meanings: 0 means "use the default action" (See NOTES below), 1 means "ignore this signal". 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 signal in order to restore a previous action definition. A negative returned value is the negation of a system error code. (See perror(3F)) FILES
/usr/lib/libU77.a SEE ALSO
signal(3C), kill(3F), kill(1) NOTES
f77 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 will be passed the signal number as an integer argument. 4.2 Berkeley Distribution May 15, 1985 SIGNAL(3F)

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sigset(3C)																sigset(3C)

NAME
sigset(), sighold(), sigrelse(), sigignore() - signal management SYNOPSIS
DESCRIPTION
The system defines a set of signals that can be delivered to a process. The set of signals is defined in signal(5), along with the meaning and side effects of each signal. An alternate mechanism for handling these signals is defined here. The facilities described here should not be used in conjunction with the other facilities described under signal(2) and sigspace(2). allows the calling process to choose one of four ways to handle the receipt of a specific signal. sig specifies the signal and func speci- fies the action handler. sig can be any one of the signals described under signal(5) except or func is assigned one of four values: or a function address. The actions prescribed by and are described under signal(5). The action pre- scribed by and function address are described below: Hold signal. The signal sig is held upon receipt. Any pending signal of this signal type remains held. Only one signal of each type is held. Note: the signals and cannot be held. function address Catch signal. func must be a pointer to a function, the signal-catching handler, that is called when signal sig occurs. specifies that the process calls this function upon receipt of signal sig. Any pending signal of this type is released. This handler address is retained across calls to the other signal management functions listed here. Upon receipt of signal sig, the receiving process executes the signal-catching function pointed to by func as described under signal(5) with the follow- ing differences: Before calling the signal-catching handler, the defined action of sig is set to During a normal return from the signal- catching handler, the defined action is restored to func and any held signal of this type is released. If a non-local goto (longjmp(3C)) is taken, must be called to restore the defined action to func and release any held signal of this type. holds the signal sig. restores the defined action of sig to that specified previously by and are used to establish critical regions of code. is analogous to raising the priority level and deferring or holding a signal until the priority is lowered by sets the action for signal sig to (see signal(5)). RETURN VALUE
Upon successful completion, returns the previous value of the defined action for the specified signal sig. Otherwise, a value of is returned and is set to indicate the error. is defined in For the other functions, a 0 value indicates that the call succeeded. A -1 return value indicates an error occurred and is set to indicate the reason. ERRORS
fails and the defined action for sig is not changed if any of the following occur: The func argument points to memory that is not a valid part of the process address space. Reliable detection of this error is implementation dependent. and and fail and the defined action for sig is not changed if any of the following occur: sig is not a valid signal number. An attempt is made to ignore, hold, or supply a handler for a signal that cannot be ignored, held, or caught; see signal(5). WARNINGS
These signal facilities should not be used in conjunction with signal(2) and sigspace(2). SEE ALSO
kill(1), kill(2), pause(2), signal(2), sigspace(2), wait(2), abort(3C), setjmp(3C), sigpause(3C), signal(5). STANDARDS CONFORMANCE
sigset(3C)

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