CODEWITHSUNDEEP
cunixpipesignalssignal-handling
Dhawal Rank
Dhawal Rank

Reputation: 1

CTRL+C and CTRL+Z signals won't block in C

I have written following code for a simple 3 player game in C.

Flow:

1) Ask user for winning score

2) 3 children are generated

3) Each will generate random scores and accumulate it

4) Whoever reaches winning score wins and terminates the program.

void sigHandler(){}
void player(char *, int *, int *, int);
int main(int argc, char *argv[])
{
    int fd1[2], fd2[2], fd3[2], fd4[2], fd5[2], fd6[2], win;
    char turn='T';
    write(1, "This is a 3 player game with a Referee\n", 38);
    printf("Enter the winning score:\n");
    scanf("%d", &win);
    pipe(fd1);
    pipe(fd2);
    if(!fork())
        player("TOTO", fd1, fd2, win);
    sleep(1);
    close(fd1[0]);
    close(fd2[1]);

    pipe(fd3);
    pipe(fd4);
    if(!fork())
        player("TITI", fd3, fd4, win);
    sleep(1);
    close(fd3[0]);
    close(fd4[1]);

    pipe(fd5);
    pipe(fd6);
    if(!fork())
        player("TUTU", fd5, fd6, win);
    sleep(1);
    close(fd5[0]);
    close(fd6[1]);
    while(1)
    {
        signal(SIGINT, sigHandler);
        signal(SIGSTOP, sigHandler);
        write(1,"\nRefree: TOTO plays\n\n", 21);
        write(fd1[1], &turn, 1);
        read(fd2[0], &turn, 1);

        write(1,"\nRefree: TITI plays\n\n", 21);
        write(fd3[1], &turn, 1);
        read(fd4[0], &turn, 1);

        write(1,"\nRefree: TUTU plays\n\n", 21);
        write(fd5[1], &turn, 1);
        read(fd6[0], &turn, 1);
    }
}
void player(char *s, int *fd1, int *fd2, int win)
{
    int points=0, dice;
    char turn;
    srand(time(NULL));
    while(1)
    {
        signal(SIGINT, sigHandler);
        signal(SIGSTOP, sigHandler);
        read(fd1[0], &turn, 1);
        printf("%s: Playing my dice\n",s);
        dice =rand() % 20 + 1;
        printf("%s: got %d points\n", s, dice);
        points+=dice;
        printf("%s: Total so far %d\n\n", s, points);
        if(points>=win)
        {
            printf("%s: GAME OVER. I WON.\n", s);
            kill(0, SIGTERM);
        }
        sleep(3);
        write(fd2[1], &turn, 1);
    }
}

The issue is I am trying to block CTRL+Z and CTRL+C signals when the program is executing but it's not working when I use following code blocks:

signal(SIGINT, sigHandler);
signal(SIGSTOP, sigHandler);

Please provide some suggestions.

Upvotes: 0

Views: 1021

Answers (2)

apfel
apfel

Reputation: 101

Just to add something up to @Thomas's answer I'll just provide you a link that I myself found useful when working with signals.

https://www.usna.edu/Users/cs/aviv/classes/ic221/s16/lec/19/lec.html

P.S: As Thomas aforementioned it's a really neat and classy idea to use SIG_IGN instead of "dummy" signal handlers.

Upvotes: 0

Thomas Dickey
Thomas Dickey

Reputation: 54525

Better than a dummy handler is using the predefined SIG_IGN (ignore):

signal(SIGINT, SIG_IGN);   /* ignore Terminal interrupt signal */
signal(SIGTSTP, SIG_IGN);  /* ignore Terminal stop signal */

Further reading:

Upvotes: 1

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