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signal

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 a 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 of 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: -
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 handler.

-

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 (in other words, the signal handler is asynchronous), the behavior is undefined if

-

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

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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.

-

Besides abort and raise, POSIX specifies that kill, pthread_kill, and sigqueue generate synchronous signals.

-

POSIX recommends sigaction instead of signal, due to its underspecified behavior and significant implementation variations, regarding signal delivery while a signal handler is executed.

-

Example

#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

References

See also

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

- © cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
- https://en.cppreference.com/w/c/program/signal -

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