[linux]signal函数不起作用

#include "apue.h"

#include <sys/wait.h>

static void sig_int(int); /* our signal-catching function */

int main(int argc, char *argv[])
{
    printf("uid = %d, gid = %d\n", getuid(), getgid());
    
    char buf[MAXLINE]; /* from apue.h */
    pid_t pid;
    int status;
    
    
    // register the signal handler
    if ( signal(SIGINT, sig_int) == SIG_ERR)
        err_sys("signal error");
    
    printf("%% "); /* print prompt (printf requires %% to print %) */
    while (fgets(buf, MAXLINE, stdin) != NULL) {
        if (buf[strlen(buf) - 1] == ‘\n‘)
            buf[strlen(buf) - 1] = 0; /* replace newline with null */
        if ((pid = fork()) < 0) {
            err_sys("fork error");
        } else if (pid == 0) { /* child */
            execlp(buf, buf, (char *)0);
            err_ret("couldn‘t execute: %s", buf);
            exit(127);
        }
        /* parent */
        if ((pid = waitpid(pid, &status, 0)) < 0)
            err_sys("waitpid error");
        printf("Last pid: %ld\n", (long)pid);
        printf("%% ");
    }
    
    exit(0);
}

void sig_int(int signo)
{
    printf("sig_int: interrupt\n%% ");
    exit(0); // I add this line to exit the program through CTRL+C (SIGINT), CTRL+D is to terminate the program
}