signal—specify handler subroutine for a signalSynopsis
#include <signal.h> void (*signal(int sig, void(*func)(int))) (int); void (*_signal_r(void *reent, int sig, void(*func)(int))) (int);
Description
signal provides a simple signal-handling implementation for embedded
targets.
signal allows you to request changed treatment for a particular
signal sig. You can use one of the predefined macros SIG_DFL
(select system default handling) or SIG_IGN (ignore this signal)
as the value of func; otherwise, func is a function pointer
that identifies a subroutine in your program as the handler for this signal.
Some of the execution environment for signal handlers is
unpredictable; notably, the only library function required to work
correctly from within a signal handler is signal itself, and
only when used to redefine the handler for the current signal value.
Static storage is likewise unreliable for signal handlers, with one
exception: if you declare a static storage location as ‘volatile
sig_atomic_t’, then you may use that location in a signal handler to
store signal values.
If your signal handler terminates using return (or implicit
return), your program’s execution continues at the point
where it was when the signal was raised (whether by your program
itself, or by an external event). Signal handlers can also
use functions such as exit and abort to avoid returning.
The alternate function _signal_r is the reentrant version.
The extra argument reent is a pointer to a reentrancy structure.
Returns
If your request for a signal handler cannot be honored, the result is
SIG_ERR; a specific error number is also recorded in errno.
Otherwise, the result is the previous handler (a function pointer or one of the predefined macros).
Portability
ANSI C requires signal.
No supporting OS subroutines are required to link with signal, but
it will not have any useful effects, except for software generated signals,
without an operating system that can actually raise exceptions.