signal - cppreference.com (original) (raw)

| | | | | -------------------------------------------------------- | | | | 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.

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[edit] Parameters

sig - the signal to set the signal handler to. It can be an implementation-defined value or one of the following values:
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:

[edit] Return value

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

[edit] 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

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.

[edit] 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.

[edit] 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

[edit] References

[edit] See also