• 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:

If the signal handler is called NOT as a result of std::abort or std::raise (asynchronous signal), the behavior is undefined if

• the signal handler calls any function within the standard library, except

• std::signal with the first argument being the number of the signal currently handled (async handler can re-register itself, but not other signals).

• the signal handler refers to any object with static storage duration that is not std::atomic(since C++11) or volatilestd::sig_atomic_t.

The behavior is undefined if any signal handler performs any of the following:

• call to any library function, except the following signal-safe functions (note, in particular, dynamic allocation is not signal-safe):

• members functions of std::atomic and non-member functions from <atomic> if the atomic type they operate on is lock-free. The functions std::atomic_is_lock_free and std::atomic::is_lock_free are signal-safe for any atomic type.
• std::signal with the first argument being the number of the signal currently handled (signal handler can re-register itself, but not other signals).
• member functions of std::numeric_limits
• The member functions of std::initializer_list and the std::initializer_list overloads of std::begin and std::end
• std::forward, std::move, std::move_if_noexcept
• All functions from <type_traits>
• std::memcpy and std::memmove

• access to an object with thread storage duration
• a dynamic_cast expression
• a throw expression
• entry to a try block, including function-try-block
• initialization of a static variable that performs dynamic non-local initialization (including delayed until first ODR-use)
• waits for completion of initialization of any variable with static storage duration due to another thread concurrently initializing it

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
• objects of lock-free std::atomic types (since C++11)
• side effects made visible through std::atomic_signal_fence(since C++11)

On return from a signal handler, the value of any object modified by the signal handler that is not volatilestd::sig_atomic_t or lock-free std::atomic is indeterminate.

A call to the function signal()synchronizes-with any resulting invocation of the signal handler.

If a signal handler is executed as a result of a call to std::raise (synchronously), then the execution of the handler is sequenced-after the invocation of std::raise and sequenced-before the return from it and runs on the same thread as std::raise. Execution of the handlers for other signals is unsequenced with respect to the rest of the program and runs on an unspecified thread.

Two accesses to the same object of type volatilestd::sig_atomic_t do not result in a data race if both occur in the same thread, even if one or more occurs in a signal handler. For each signal handler invocation, evaluations performed by the thread invoking a signal handler can be divided into two groups A and B, such that no evaluations in B happen-before evaluations in A, and the evaluations of such volatilestd::sig_atomic_t objects take values as though all evaluations in A happened-before the execution of the signal handler and the execution of the signal handler happened-before all evaluations in B.

SIGABRT

(Signal Abort) Abnormal termination, such as is initiated by the function.

SIGFPE

(Signal Floating-Point Exception) Erroneous arithmetic operation, such as zero divide or an operation resulting in overflow (not necessarily with a floating-point operation).

SIGILL

(Signal Illegal Instruction) Invalid function image, such as an illegal instruction. This is generally due to a corruption in the code or to an attempt to execute data.

SIGINT

(Signal Interrupt) Interactive attention signal. Generally generated by the application user.

SIGSEGV

(Signal Segmentation Violation) Invalid access to storage − When a program tries to read or write outside the memory it is allocated for it.

SIGTERM

(Signal Terminate) Termination request sent to program.

SIG_DFL

Default handling − The signal is handled by the default action for that particular signal.

SIG_IGN

Ignore Signal − The signal is ignored.