Signals are invoked, or raised, using the raise() function. When a signal is raised its associated function is executed.

With the Metrowerks C implementation of signal.h a signal can only be invoked through the function "raise", and, in the case of the SIGABRT signal, through the function "abort". When a signal is raised, its signal handling function is executed as a normal function call.

The default signal handler for all signals except SIGTERM is SIG_DFL. The SIG_DFL function aborts a program with the abort() function, while the SIGTERM signal terminates a program normally with the exit() function.

The ANSI C Standard Library specifies that the SIG prefix used by the signal.h macros is reserved for future use. The programmer should avoid using the prefix to prevent conflicts with future specifications of the Standard Library.

The type typedef char sig_atomic_t in signal.h can be accessed as an incorruptible, atomic entity during an asynchronous interrupt.

The number of signals is defined by __signal_max given a value in this header.

Macro	Description
SIGABRT	Abort signal. This macro is defined as a positive integer value. This signal is called by the abort() function.
SIGFPE	Floating point exception signal. This macro is defined as a positive integer value.
SIGILL	Illegal instruction signal. This macro is defined as a positive integer value.
SIGINT	Interactive user interrupt signal. This macro is defined as a positive integer value.
SIGSEGV	Segment violation signal. This macro is defined as a positive integer value.
SIGTERM	Terminal signal. This macro is defined as a positive integer value. When raised this signal terminates the calling program by calling the exit() function.

The signal() function specifies how a signal is handled: a signal can be ignored, handled in a default manner, or be handled by a programmer-supplied signal handling function. "Signal function handling arguments" describes the pre-defined signal handling macros.

Macro	Description
SIG_IGN	This macro expands to a pointer to a function that returns void. It is used as a function argument in signal() to designate that a signal be ignored.
SIG_DFL	This macro expands to a pointer to a function that returns void. This signal handler quits the program without flushing and closing open streams.
SIG_ERR	A macro defined like SIG_IGN and SIG_DFL as a function pointer. This value is returned when signal() cannot honor a request passed to it.