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signal

From cppreference.com
< c‎ | program
Defined in header <signal.h>
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 signal(sig, SIG_DFL) will be executed immediately before the start of signal handler. Also, the implementation can prevent some implementation-defined set af signals from occurring while the signal handler runs.

Contents

[edit] Parameters

sig - the signal to set the signal handler to. It can be an implementation-defined value or one of the following values:
defines signal types
(macro constant) [edit]


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);

[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 handle

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, the behavior is undefined if

  • the signal handler calls any function within the standard library, except abort, _Exit, quick_exit, or signal with the first argument not being the number of the signal currently handled.
  • the signal handler refers to any object with static or thread-local(since C11) storage duration that is not lock-free atomic(since C11) or volatile std::sig_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

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.

[edit] Example

#include <stdio.h>
#include <signal.h>
 
/* A user-defined signal handler can process one or more signals. */
static void signal_handler(int signo)
{
    switch(signo)
    {
        case SIGABRT : puts("Process SIGABRT signal here."); break;
        case SIGFPE  : puts("Process SIGFPE  signal here."); break;
        case SIGILL  : puts("Process SIGILL  signal here."); break;
        case SIGINT  : puts("Process SIGINT  signal here."); break;
        case SIGSEGV : puts("Process SIGSEGV signal here."); break;
        case SIGTERM : puts("Process SIGTERM signal here."); break;
    }
 
    /* some cleanup here */
    /* exit(signo);      */
}
 
int main(void)
{
    /* Register a user-defined signal handler. */
    signal(SIGABRT, signal_handler);
    signal(SIGFPE,  signal_handler);
    signal(SIGILL,  signal_handler);
    signal(SIGINT,  signal_handler);
    signal(SIGSEGV, signal_handler);
    signal(SIGTERM, signal_handler);
 
    /* Raise a signal. */
    raise(SIGABRT);
    raise(SIGFPE);
    raise(SIGILL);
    raise(SIGINT);
    raise(SIGSEGV);
    raise(SIGTERM);
 
    return 0;
}

Output:

Process SIGABRT signal here.
Process SIGFPE  signal here.
Process SIGILL  signal here.
Process SIGINT  signal here.
Process SIGSEGV signal here.
Process SIGTERM signal here.

[edit] See also

runs the signal handler for particular signal
(function) [edit]