Signal Handling (`signal.h')

A signal is an event that interrupts the normal flow of control in your program. Your operating environment normally defines the full set of signals available (see `sys/signal.h'), as well as the default means of dealing with them--typically, either printing an error message and aborting your program, or ignoring the signal.

All systems support at least the following signals:

SIGABRT

Abnormal termination of a program; raised by the <<abort>> function.

SIGFPE

A domain error in arithmetic, such as overflow, or division by zero.

SIGILL

Attempt to execute as a function data that is not executable.

SIGINT

Interrupt; an interactive attention signal.

SIGSEGV

An attempt to access a memory location that is not available.

SIGTERM

A request that your program end execution.

Two functions are available for dealing with asynchronous signals--one to allow your program to send signals to itself (this is called raising a signal), and one to specify subroutines (called handlers to handle particular signals that you anticipate may occur--whether raised by your own program or the operating environment.

To support these functions, `signal.h' defines three macros:

SIG_DFL

Used with the signal function in place of a pointer to a handler subroutine, to select the operating environment's default handling of a signal.

SIG_IGN

Used with the signal function in place of a pointer to a handler, to ignore a particular signal.

SIG_ERR

Returned by the signal function in place of a pointer to a handler, to indicate that your request to set up a handler could not be honored for some reason.

`signal.h' also defines an integral type, sig_atomic_t. This type is not used in any function declarations; it exists only to allow your signal handlers to declare a static storage location where they may store a signal value. (Static storage is not otherwise reliable from signal handlers.)

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