C library functions -sigaction()

C Standard Library - <signal.h>

sigactionThe function is a C standard library function used to check or modify the handling action associated with a specific signal. WithsignalCompared with the function,sigactionProvides more control and better portability.

Syntax

int sigaction(int sig, const struct sigaction *act, struct sigaction *oldact);

Parameter

  • int sig: The signal number to inspect or modify. Common signals includeSIGINT、SIGTERM、SIGKILLetc.
  • const struct sigaction *act: A pointer to the new signal handling action. If it isNULL, the current signal handling action is not modified.
  • struct sigaction *oldact: A pointer to save the old signal handling action. If it isNULL, the old signal handling action is not saved.

struct sigactionStructure

struct sigaction {
    void (*sa_handler)(int);           // 信号处理函数指针
    void (*sa_sigaction)(int, siginfo_t *, void *); // 信号处理函数指针（扩展）
    sigset_t sa_mask;                  // 在处理该信号时要阻塞的信号集
    int sa_flags;                      // 修改信号行为的选项
    void (*sa_restorer)(void);         // 恢复函数，已废弃
};

sa_flagscommon options

  • SA_RESTART: Automatically restart system calls interrupted by the signal.
  • SA_SIGINFO: Usesa_sigactioninstead ofsa_handleras a signal handling function.
  • SA_NOCLDSTOP: ifsigYesSIGCHLD, the signal is not generated when a child process stops or continues.

Return Value

  • Returns 0 on success.
  • On failure, returns -1 and setserrnoto indicate the type of error.

Example

The following is a simple example program demonstrating how to usesigactionFunction settingsSIGINTSignal handler:

Example

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

// Custom signal handling function
void handle_sigint(int sig) {
    printf("Caught signal %d\n", sig);
}

int main() {
    struct sigaction sa;

    // Set the handler to handle_sigint
    sa.sa_handler = handle_sigint;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;

    // Use sigaction to set the new signal handling action
    if (sigaction(SIGINT, &sa, NULL) == -1) {
        perror("sigaction");
        return 1;
    }

    // Main loop, keeps running until a signal is caught
    while (1) {
        printf("Running...\n");
        sleep(1);
    }

    return 0;
}

After compiling and running the program, the output will be:

Running...
Running...
Running...
...

When Ctrl+C is pressed (sendingSIGINTsignal), the output will be:

Caught signal 2

The program caughtSIGINTsignal and execute a custom signal handling functionhandle_sigint, and then continue running the main loop.

Notes

  • sigactionThe function provides more thansignalThe function provides richer functionality, allowing you to set signal handlers, signal masks, and signal handling options.
  • The signal handling function should be as short as possible, because other signals are blocked while handling a signal. If the signal handling function runs for too long, it may affect the real-time performance of the program.
  • Certain signals (such asSIGKILLandSIGSTOP) cannot be caught or ignored.

C Standard Library - <signal.h>

other extensions