C++: stopping a while loop from outside

Franz · 2008-11-13 14:46:41

I have a class. And in that class, I have a loop like this:

while (true) {
  if (check) {
    break;
  }

  ....
}

Can I access the check variable from another class function during runtime?

Smartys · 2008-11-13 15:36:10

If you define check outside of the while loop. Of course, in a single-threaded app, another class won't be able to set check once you're in the while loop because you'll be looping.
(I don't actually know C++, but there's no reason for me to believe this is wrong).

Reines · 2008-11-13 15:54:11

What Smartys said. Also is there any reason to use that instead of:

while (!check) {
    ...
}

Franz · 2008-11-14 15:14:47

@reines... uhmmm no. you're right. any ideas how i could do it instead?

Last edited by Franz (2010-08-09 20:51:11)

jmp · 2008-11-14 15:30:31

lie2815 wrote:

@reines... uhmmm know. you're right. any ideas how i could do it instead?

Didn't he just say it?

Franz · 2008-11-15 12:58:50

Well, as Smartys said (and as Reines referenced Smartys), this won't work in a single-threaded app...

But I found a solution. Never mind.

Strofanto · 2008-11-15 13:21:51

Shouldn't you use return instead of break?

Last edited by Strofanto (2008-11-15 13:24:51)

Franz · 2008-11-15 13:24:27

I don't think so. Same effect, but also same problem... single-threaded app.

I'll just refrain from doing an infinite loop

dotme · 2008-11-15 13:31:53

Even in a single-threaded application you might use signal handlers like SIGALRM.

Franz · 2008-11-15 13:34:38

Could you explain a little more? I am not that experienced. Thank you.

dotme · 2008-11-15 13:48:10

In Unix you can schedule an alarm (man alarm, man ualarm), which causes a signal of type SIGALRM send to you app. Before issuing the alarm, you have to setup a signal handler (sigaction ?) which acts on SIGALRM. You should ask google for some more details and examples.

Anyway your class has to make the variable "check" accessible from outside and you have to keep a reference to your class-instance on which you signal handler can act.

Franz · 2008-11-15 13:50:29

Well, thank you. I will probably have a look at that later, but I'll just choose the simple way (see above) for this project, since I don't have enough time...

Thanks.

frozen_space · 2008-11-16 12:08:23

you can write a value to a file, and within that loop, check the value of the file

Franz · 2008-11-16 13:06:21

I would still need to be able to write to that file while doing the loop... but thx

bjorn · 2008-11-18 08:52:57

The only thing saving you in a single threaded application would be interrupts. And in most x86 compilers even interrupts are handled in-thread, so you're mostly stuck. Implenting threading in cpp is VERY easy though.

That being said, a problem needing a solution like the one you're explaining mostly represents bad logic and coding. mind telling us more about what you really want to do?

Franz · 2008-11-18 14:45:18

It's actually done, but the topic is interesting...

I was working on a simulation of a street with two gas stations. Every second there is a car, 1 of 60 cars stops and so on...

I hope that's enough explanation.

Kaboon · 2008-11-19 12:56:35

lie2815 wrote:

It's actually done, but the topic is interesting...
I was working on a simulation of a street with two gas stations. Every second there is a car, 1 of 60 cars stops and so on...
I hope that's enough explanation.

Couldn't that just be easily be done by doing;

    if((CURRENT_CAR % 60) == 0)
        // do some kind of action here

in the loop or am I missing the point here?

Last edited by Kaboon (2008-11-19 12:56:51)

Franz · 2008-11-19 18:16:06

It's a simulation. It's done randomly.

if (random(60) == 59)
   newCar();

Forums

#1 2008-11-13 14:46:41

C++: stopping a while loop from outside

#2 2008-11-13 15:36:10

Re: C++: stopping a while loop from outside

#3 2008-11-13 15:54:11

Re: C++: stopping a while loop from outside

#4 2008-11-14 15:14:47

Re: C++: stopping a while loop from outside

#5 2008-11-14 15:30:31

Re: C++: stopping a while loop from outside

#6 2008-11-15 12:58:50

Re: C++: stopping a while loop from outside

#7 2008-11-15 13:21:51

Re: C++: stopping a while loop from outside

#8 2008-11-15 13:24:27

Re: C++: stopping a while loop from outside

#9 2008-11-15 13:31:53

Re: C++: stopping a while loop from outside

#10 2008-11-15 13:34:38

Re: C++: stopping a while loop from outside

#11 2008-11-15 13:48:10

Re: C++: stopping a while loop from outside

#12 2008-11-15 13:50:29

Re: C++: stopping a while loop from outside

#13 2008-11-16 12:08:23

Re: C++: stopping a while loop from outside

#14 2008-11-16 13:06:21

Re: C++: stopping a while loop from outside

#15 2008-11-18 08:52:57

Re: C++: stopping a while loop from outside

#16 2008-11-18 14:45:18

Re: C++: stopping a while loop from outside

#17 2008-11-19 12:56:35

Re: C++: stopping a while loop from outside

#18 2008-11-19 18:16:06

Re: C++: stopping a while loop from outside

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