SIGNAL(P) POSIX Programmer's Manual SIGNAL(P)
signal - signal management
void (*signal(int sig, void (*func)(int)))(int);
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. Other-
wise, the application shall ensure that func points to a function to be called when that
signal occurs. An invocation of such a function because of a signal, or (recursively) of
any further functions called by that invocation (other than functions in the standard
library), is called a "signal handler".
When a signal occurs, and func points to a function, it is implementation-defined whether
the equivalent of a:
is executed or the implementation prevents some implementation-defined set of signals (at
least including sig) from occurring until the current 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:
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 excep-
tion, 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 storage 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:
is executed for some signals, and the equivalent of:
is executed for all other signals (see exec).
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. Otherwise, SIG_ERR shall be returned and a
positive value shall be stored in errno.
The signal() function shall fail if:
EINVAL The sig argument is not a valid signal number or an attempt is made to catch a sig-
nal 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.
The sigaction() function provides a more comprehensive and reliable mechanism for control-
ling signals; new applications should use sigaction() rather than signal().
Signal Concepts , exec() , pause() , sigaction() , sigsuspend() , waitid() , the Base Def-
initions volume of IEEE Std 1003.1-2001, <signal.h>
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 SIGNAL(P)