std::signal
std::signal
| Defined in header | | |
|---|---|---|
| /*signal-handler*/* signal(int sig, /*signal-handler*/* handler | (1) | |
| extern "C" using /*signal-handler*/ = void(int // exposition-only | (2) | |
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 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).
(Note: POSIX introduced sigaction to standardize these implementation-defined behaviors).
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) | SIGABRTSIGFPESIGILLSIGINTSIGSEGVSIGTERM | defines signal types (macro constant) |
|---|---|---|---|---|
| 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 | void fun(int sig | |
| void fun(int sig | | |
SIG_DFLmacro. The signal handler is set to default signal handler.
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, SIGSEGV or any other implementation-defined signal specifying a computational exception, the behavior is undefined.
If the signal handler is called as a result of std::abort or std::raise, the behavior is undefined if the signal handler calls std::raise.
If the signal handler is called NOT as a result of std::abort or std::raise, the behavior is undefined if.
- the signal handler calls any function within the standard library, except
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
volatilestd::sig_atomic_t
On return from a signal handler, the value of any object modified by the signal handler that is not volatile std::sig_atomic_t or std::atomic is undefined.
The behavior is undefined if std::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.
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
#include <csignal>
#include <iostream>
namespace
{
volatile std::sig_atomic_t gSignalStatus;
}
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 |
| atomic_signal_fence (C++11) | fence between a thread and a signal handler executed in the same thread (function) |
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