signal

 

C

Language

Standard Library

Type support

Dynamic memory management

Error handling

Program utilities

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

 

Program support utilities

Program termination
abort exit quick_exit (C++11) _Exit (C++11)	atexit at_quick_exit (C++11) EXIT_SUCCESSEXIT_FAILURE
Communicating with the environment
system	getenv
Signals
signal raise sig_atomic_t	SIG_DFLSIG_IGN SIG_ERR
Signal types
SIGABRTSIGFPESIGILLSIGINTSIGSEGVSIGTERM
Non-local jumps
setjmp
longjmp
Types
jmp_buf

 

Defined in header <signal.h>
void (*signal( int sig, void (*handler) (int))) (int);

Sets the error handler for signal sig. The signal handler can be set so that default handling will occur, signal is ignored, or an user-defined function is called.

When signal handler is set to a function and a signal occurs, it is implementation defined whether signal(sig, SIG_DFL) will be executed immediately before the start of signal handler. Also, the implementation can prevent some implementation-defined set af signals from occurring while the signal handler runs.

Parameters

sig	-	the signal to set the signal handler to. It can be an implementation-defined value or one of the following values: SIGABRTSIGFPESIGILLSIGINTSIGSEGVSIGTERM defines signal types (macro constant)
handler	-	the signal handler. This must be one of the following: SIG_DFL macro. The signal handler is set to default signal handler. SIG_IGN macro. The signal is ignored. pointer to a function. The signature of the function must be equivalent to the following: void fun(int sig);

Return value

Previous signal handler on success or SIG_ERR on failure (setting a signal handler can be disabled on some implementations).

Signal handler

The following limitations are imposed on the user-defined function that is installed as a signal handle

If the user defined function returns when handling SIGFPE, SIGILL or SIGSEGV, the behavior is undefined.

If the signal handler is called as a result of abort or raise, the behavior is undefined if the signal handler calls raise.

If the signal handler is called NOT as a result of abort or raise, the behavior is undefined if

• the signal handler calls any function within the standard library, except abort, _Exit, quick_exit, or signal with the first argument not being the number of the signal currently handled.
• the signal handler refers to any object with static or thread-local(since C11) storage duration that is not lock-free atomic(since C11) or volatile std::sig_atomic_t.

On entry to the signal handler, the state of the floating-point environment and the values of all objects is unspecified, except for

• objects of type volatile sig_atomic_t
• objects of lock-free atomic types (since C11)
• side effects made visible through atomic_signal_fence (since C11)

On return from a signal handler, the value of any object modified by the signal handler that is not volatile sig_atomic_t or lock-free atomic(since C11) is undefined.

The behavior is undefined if signal is used in a multithreaded program. It is not required to be thread-safe.

Notes

POSIX requires that signal is thread-safe, and specifies a list of async-signal-safe library functions that may be called from any signal handler.

Example

Run this code

#include <signal.h>
#include <stdio.h>
 
volatile sig_atomic_t gSignalStatus;
 
void signal_handler(int signal)
{
  gSignalStatus = signal;
}
 
int main(void)
{
  signal(SIGINT, signal_handler);
 
  printf("SignalValue: %d\n", gSignalStatus);
  printf("Sending signal: %d\n", SIGINT);
  raise(SIGINT);
  printf("SignalValue: %d\n", gSignalStatus);
}

Output:

SignalValue: 0
Sending signal: 2
SignalValue: 2

See also

raise	runs the signal handler for particular signal (function)
C++ documentation for signal