C signal handling

In the

Standard signals

The C standard defines only 6 signals. They are all defined in signal.h header (csignal header in C++):^[1]

• SIGABRT – "abort", abnormal termination.
• SIGFPE –
  floating point exception
  .
• SIGILL – "illegal", invalid instruction.
• SIGINT – "interrupt", interactive attention request sent to the program.
• SIGSEGV – "
  segmentation violation
  ", invalid memory access.
• SIGTERM – "terminate", termination request sent to the program.

Additional signals may be specified in the signal.h header by the implementation. For example, Unix and

• SIGTRAP for debugging purposes. It's platform-dependent and may be used on Unix-like operating systems.

Handling

A signal can be generated by calling raise() or kill() system calls. raise() sends a signal to the current process, kill() sends a signal to a specific process.

A signal handler is a

Signal handlers can be set with signal() or sigaction(). The behavior of signal() has been changed multiple times across history and its use is discouraged.

If the signal reports an error within the program (and the signal is not asynchronous), the signal handler can terminate by calling abort(), exit(), or longjmp().

Functions

Example usage

#include <signal.h>
#include <stdio.h>
#include <stdlib.h>

volatile sig_atomic_t status = 0;

static void catch_function(int signo) {
    status = signo;
}

int main(void) {
    // Set above function as signal handler for the SIGINT signal:
    if (signal(SIGINT, catch_function) == SIG_ERR) {
        fputs("An error occurred while setting a signal handler.\n", stderr);
        return EXIT_FAILURE;
    }
    puts("Raising the interactive attention signal.");
    if (raise(SIGINT)) {
        fputs("Error raising the signal.\n", stderr);
        return EXIT_FAILURE;
    }
    if (status == SIGINT) puts("Interactive attention signal caught.");
    puts("Exiting.");
    return EXIT_SUCCESS;
    // exiting after raising signal
}

See also

• Unix signal

References