How can I break a loop when a specific character has been hit?

Question

Assume I have a loop like

for(int i = 0; i < 100000; i++)
{
    crunch_data(i);

    if(i_has_been_hit())
        break;
}

and I would like to exit the loop whenever I hit i on the keyboard. Now the following approach won't work, since std::cin blocks:

bool i_has_been_hit(){
    char a;
    std::cin >> a;
    return a == 'i';
}

Is there a function which enables me to check whether the keyboard has been hit without blocking? If it makes any difference, I'm using g++ on Win32 with CodeBlocks.

PLZ answer,i want my loop running and when i punch a button my loop will break — Vio, Mar 27 '14 at 12:31
Afaik there is no platform independend way to do this. Do you have to use it for multiple systems? — MatthiasB, Mar 27 '14 at 12:32
http://stackoverflow.com/questions/3317740/checking-data-availability-before-calling-stdgetline — 001, Mar 27 '14 at 12:32
You may have to use 'curses' for this. I don't think there is a good platform independent way to do this. — Abhishek Bansal, Mar 27 '14 at 12:32
then it would be a good time to specify the platform you're using in your question ;) — MatthiasB, Mar 27 '14 at 12:33
my loop printing the " HI",it dosen't wait for my Entering,when i want ,i Enter a char and my loop will break,this is what i want — Vio, Mar 27 '14 at 12:36
@user3260217: Specify your platform. Win32? POSIX? What compiler? — Zeta, Mar 27 '14 at 12:37

score 0 · Answer 1 · answered Mar 27 '14 at 12:32

0

Did you mean a perfect non-blocking I/O model ?? If so its hard to achive and i dont know any existing ways to do it, But u can do something like this

use _kbhit()

for(int i=0;i<100000;i++)
{
    cout<<"Hi";
    while (true) {
          if (_kbhit()) {
        char a = _getch();
        // act on character a in whatever way you want
    }

    Sleep(100);
    if(a=='i')
       break;
}

answered Mar 27 '14 at 12:32

Amarnath R Shenoy

5,121
8
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my loop printing the " HI",it dosen't wait for my Entering,when i want ,i Enter a char and my loop will break,this is what i want – Vio Mar 27 '14 at 12:37
1

title says "How to get character without stop loop in c++". Perhaps you should make up your mind – Alexander Tobias Bockstaller Mar 27 '14 at 12:52
1

:) SOLVED ,sorry i will never make this mistake – Vio Mar 27 '14 at 12:56

score 0 · Accepted Answer · answered Mar 27 '14 at 12:49

0

If you are using Win32 with conio.h available, you can use the usual kbhit() and getch() combination:

#include <conio.h>
#include <iostream>

int main(){
  for(int i=0;i<100000;i++)
  {
      std::cout<<"Hi";
      if(kbhit() && getch() == 'i'){
          break;
      }
      // other code
  }
}

answered Mar 27 '14 at 12:49

Zeta

103,620
13
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@user3260217: You would have gotten answers sooner if your question's quality was higher. Please try to write the perfect question next time, see http://java.dzone.com/articles/how-write-perfect and https://msmvps.com/blogs/jon_skeet/archive/2010/08/29/writing-the-perfect-question.aspx for guidelines. – Zeta Mar 27 '14 at 13:01

How can I break a loop when a specific character has been hit?

2 Answers2