Sets the error handler for signalsig. 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 whethersignal(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.

[edit]Parameters

[edit]Return value

Previous signal handler on success orSIG_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 handlingSIGFPE,SIGILL orSIGSEGV, the behavior is undefined.

If the signal handler is called as a result ofabort orraise, the behavior is undefined if the signal handler callsraise.

If the signal handler is called NOT as a result ofabort orraise (in other words, the signal handler isasynchronous), the behavior is undefined if

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

• abort
• _Exit
• quick_exit
• signal with the first argument being the number of the signal currently handled (async handler can re-register itself, but not other signals).
• atomic functions from<stdatomic.h> if the atomic arguments are lock-free
• atomic_is_lock_free (with any kind of atomic arguments)

• the signal handler refers to any object with staticor thread-local(since C11)storage durationthat is not a lock-freeatomic(since C11) other than by assigning to a staticvolatilesig_atomic_t.

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 typevolatilesig_atomic_t
• objects of lock-free atomic types(since C11)
• side effects made visible throughatomic_signal_fence(since C11)

On return from a signal handler, the value of any object modified by the signal handler that is notvolatilesig_atomic_t or lock-free atomic(since C11) is undefined.

The behavior is undefined ifsignal is used in a multithreaded program. It is not required to be thread-safe.

[edit]Notes

POSIX requires thatsignal is thread-safe, andspecifies a list of async-signal-safe library functions that may be called from any signal handler.

Besidesabort andraise, POSIX specifies thatkill,pthread_kill, andsigqueue generate synchronous signals.

POSIX recommendssigaction instead ofsignal, 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> volatilesig_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);}

SignalValue: 0Sending signal: 2SignalValue: 2

[edit]References

[edit]See also

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