SIGNAL(P) POSIX Programmer's Manual SIGNAL(P)NAMEsignal - signal management
SYNOPSIS
#include <signal.h>
void (*signal(int sig, void (*func)(int)))(int);
DESCRIPTION
Use of this function is unspecified in a multi-threaded process.
The signal() function chooses one of three ways in which receipt of the
signal number sig is to be subsequently handled. If the value of func
is SIG_DFL, default handling for that signal shall occur. If the value
of func is SIG_IGN, the signal shall be ignored. Otherwise, the appli‐
cation shall ensure that func points to a function to be called when
that signal occurs. An invocation of such a function because of a sig‐
nal, or (recursively) of any further functions called by that invoca‐
tion (other than functions in the standard library), is called a "sig‐
nal handler".
When a signal occurs, and func points to a function, it is implementa‐
tion-defined whether the equivalent of a:
signal(sig, SIG_DFL);
is executed or the implementation prevents some implementation-defined
set of signals (at least including sig) from occurring until the cur‐
rent signal handling has completed. (If the value of sig is SIGILL, the
implementation may alternatively define that no action is taken.) Next
the equivalent of:
(*func)(sig);
is executed. If and when the function returns, if the value of sig was
SIGFPE, SIGILL, or SIGSEGV or any other implementation-defined value
corresponding to a computational exception, the behavior is undefined.
Otherwise, the program shall resume execution at the point it was
interrupted. If the signal occurs as the result of calling the abort(),
raise(), kill(), pthread_kill(), or sigqueue() function, the signal
handler shall not call the raise() function.
If the signal occurs other than as the result of calling abort(),
raise(), kill(), pthread_kill(), or sigqueue(), the behavior is
undefined if the signal handler refers to any object with static stor‐
age duration other than by assigning a value to an object declared as
volatile sig_atomic_t, or if the signal handler calls any function in
the standard library other than one of the functions listed in Signal
Concepts . Furthermore, if such a call fails, the value of errno is
unspecified.
At program start-up, the equivalent of:
signal(sig, SIG_IGN);
is executed for some signals, and the equivalent of:
signal(sig, SIG_DFL);
is executed for all other signals (see exec).
RETURN VALUE
If the request can be honored, signal() shall return the value of func
for the most recent call to signal() for the specified signal sig. Oth‐
erwise, SIG_ERR shall be returned and a positive value shall be stored
in errno.
ERRORS
The signal() function shall fail if:
EINVAL The sig argument is not a valid signal number or an attempt is
made to catch a signal that cannot be caught or ignore a signal
that cannot be ignored.
The signal() function may fail if:
EINVAL An attempt was made to set the action to SIG_DFL for a signal
that cannot be caught or ignored (or both).
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The sigaction() function provides a more comprehensive and reliable
mechanism for controlling signals; new applications should use sigac‐
tion() rather than signal().
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
Signal Concepts , exec() , pause() , sigaction() , sigsuspend() ,
waitid() , the Base Definitions volume of IEEE Std 1003.1-2001, <sig‐
nal.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 SIGNAL(P)
