std::signal

 

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abort exit quick_exit (C++11) _Exit (C++11)	atexit at_quick_exit (C++11) EXIT_SUCCESSEXIT_FAILURE
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unreachable (C++23)
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system	getenv
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signal raise sig_atomic_t	SIG_DFLSIG_IGN SIG_ERR
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SIGABRTSIGFPESIGILL	SIGINTSIGSEGVSIGTERM
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setjmp	longjmp
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jmp_buf

 

Defined in header <csignal>
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 std::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.

For some of the signals, the implementation may call std::signal(sig, SIG_IGN) at the startup of the program. For the rest, the implementation must call std::signal(sig, SIG_DFL).

If the user defined function returns when handling SIGFPE, SIGILL, SIGSEGV or any other implementation-defined signal specifying a computational exception, the behavior is undefined. In most implementations the program terminates.

If the signal handler is called otherwise than as a result of std::abort or std::raise, the behavior is undefined if any of the following requirements is not followed:

• the signal handler calls std::raise.
• the signal handler refers to an object of static storage duration which is not declared as volatile std::sig_atomic_t.
• the signal handler calls any function within the standard library, except std::abort, std::_Exit, or std::signal with the first argument not being the number of the signal currently handled.

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).

Notes

Signal handlers are expected to have C linkage and, in general, only use the features from the common subset of C and C++. It is implementation-defined if a function with C++ linkage can be used as a signal handler.

Example

Run this code

#include <csignal>
#include <iostream>
 
namespace
{
  volatile sig_atomic_t gSignalStatus = 0;
}
 
void signal_handler(int signal)
{
  gSignalStatus = signal;
}
 
int main()
{
  // Install a signal handler
  std::signal(SIGINT, signal_handler);
 
  std::cout << "SignalValue: " << gSignalStatus << '\n';
  std::cout << "Sending signal " << SIGINT << '\n';
  std::raise(SIGINT);
  std::cout << "SignalValue: " << gSignalStatus << '\n';
}

Possible output:

SignalValue: 0
Sending signal 2
SignalValue: 2

See also

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