How to exit from scanf after some time?

Question

I want to exit from the scanf after certain amount of time, how to proceed. Any pointer or suggestions?

Answer 1

One way is by using timer concept ,
start timer before scanf() function,set some amount of time and give one call back function in this function you need to write further steps.
OR
By using threads mechanism.
ex :

#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <setjmp.h>
jmp_buf env;
void trigger(int sig)
{
    printf("Im in trigger\n");
    longjmp(env,2);
}

int main(void)
{
    char buf[100];
    int i;

    signal(SIGALRM, trigger);
    alarm(3);
    i = setjmp(env);

    if(!i){
    scanf("%s\n",buf);
    }else{
        printf("im in else part\n");
    }

    printf("Finall ...\n");

    return 0;
}

Comments

But how to stop the current scanf processing after timer expiry?

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I dont think you can terminate scanf programmatically, as scanf terminates only of EOF.  May be you need to break the functionality to two thread one which stop at scanf and another start at the timer expiry and does the processing beyond scanf.

Whenever timer is expired stop the thread1 which is waiting for scanf and start the thread2 which has further processing. If scanf returns successfully then stop the timer.

---

Try this......

#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <setjmp.h>
jmp_buf env;
void trigger(int sig)
{
    printf("Im in trigger\n");
    longjmp(env,2);
}

int main(void)
{
    char buf[100];
        int i;


    signal(SIGALRM, trigger);
    alarm(3);
    i = setjmp(env);
    if(!i){
    scanf("%s\n",buf);
    }else{
        printf("im in else part\n");
    }

    printf("Finall ...\n");

    return 0;
}

---

Can you please explain the logic I mean role of setjmp and longjmp  :)

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if we want to skip scanf we should jump after scanf or before scanf . jumping after scanf is little bit difficut so here i used setjmp and longjmp to start execution from before the scanf .(when you call longjmp the execution will be started immediately after line setjmp()).