Thread: fork(maybe)

I want to have the user be able to input something for 5 seconds; after that, I want it to see if there was and answer and if not count it wrong(obviously if he/she did check it), but I dont' know how to get the program to ask for and input for only 5 seconds. I was first about to use sleep, but soon realized where it failed. Do I need to fork my program. If so how would I go about doing that I have never done it. And if you are wondering, I of course, run gentoo Linux.

try using select()

Check the man page of select() for a perfect example of this.

Code:

       #include <stdio.h>
       #include <sys/time.h>
       #include <sys/types.h>
       #include <unistd.h>

       int
       main(void)
       {
           fd_set rfds;
           struct timeval tv;
           int retval;

           /* Watch stdin (fd 0) to see when it has input. */
           FD_ZERO(&rfds);
           FD_SET(0, &rfds);
           /* Wait up to five seconds. */
           tv.tv_sec = 5;
           tv.tv_usec = 0;

           retval = select(1, &rfds, NULL, NULL, &tv);
           /* Don't rely on the value of tv now! */

           if (retval)
               printf("Data is available now.\n");
               /* FD_ISSET(0, &rfds) will be true. */
           else
               printf("No data within five seconds.\n");

           exit(0);
       }

I don't see how to actually get the input though. I understand it waits and sees if it is changed. I must be missing something.

Well once you know there IS input then you can use any number of different methods to get it.

Lets look at:

Code:

if (retval)
               printf("Data is available now.\n");
               /* FD_ISSET(0, &rfds) will be true. */

You can change that to:

Code:

if (retval)
{
  fgets(buffer, sizeof buffer, stdin);
}

Ah I see. Does this buffer the input from stdin so you don't miss what happened in the 5 seconds or what. This is pretty nifty. Oh and thanx Thantos

Yeah, since input is buffered by default select won't return until the user hits enter (or time elapses) and any input that the user put in will remain in the buffer till emptied. (Though if you wanted to do unbuffered input take a looky at this thread)

Okay I got that part working, but I get a minor problem. I just decided to keep it on this same thread though. Say I was in the middle of typing the answer when the time ran out. When it goes strait to the next question what I typed is still there

Code:

 while(x<input){
                bn=rand();
                bn%=99;
                bn+=1;
                if(bn<=9)
                        bn+=10; /*bignum will always be 2 digits now*/
                ln=rand();
                ln%=10;
                if(ln<2)
                        ln+=2;
                printf("\t%5i\n\t*%4i\n\t-----\n\n",bn,ln);
                FD_ZERO(&rfds);
                FD_SET(0, &rfds);
                tv.tv_sec = 6;
                tv.tv_usec = 0;
                retval=select(1, &rfds, NULL, NULL, &tv);
                canswer=ln*bn;
                if(retval){
                        fgets(buffer,sizeof buffer,stdin);
                        sscanf(buffer,"%d",&answer);
                        if((compare(answer,canswer))){
                                score++;
                                printf("Correct\n");
                                }
                        else{
                                printf("Wrong\n");
                                cscore++;
                        }
                }
                else{
                        printf("Wrong\n");
                        cscore++;
                }
                x++;
        }

this is the loop I have. Any suggestions. Oh and compare is defined like so

Code:

int compare(int num1,int num2){
        if(num1==num2)
                return 1;
        else
                return 0;
}

Any ideas to fix this?

figured it. I had another stupid prob. Thanx