How to collect keyboard input inside a loop in c++

Question

I have a program running a numerical calculations with precision increasing in time. It does so for different values of some parameters. The precision I need for each results depends on the value of these parameters, in a way totally unknown to me.

To get enough precision for each value, I am thinking about a program/loop that would cut a calculation and move on to new values of the parameters if the user hits the keyboard.

Schematically:

//initialise parameters
while( parameters_in_good_range){
     while( no_key_pressed){
         //do calculation
     }
     //update parameters
}

There's no way to poll the keyboard in standard C++, you need to rely on OS specific functions. — Mark Ransom, Sep 14 '16 at 12:00
@MarkRansom not totally agree with you: since c++11, you can create thread and have some control on it, and have some basic synchronization mechanism. So you can have a thread which do calculation and a second one which read standard input. When second receive an input, it can tell to the other that it has to quit — Garf365, Sep 14 '16 at 12:04
@Garf365 but *standard input* is different from *keyboard input*. — eerorika, Sep 14 '16 at 12:10
@close-voter: it's perfectly clear what this question is asking. It says `while(no_key_pressed){/*do calculation*/}`. — GreenAsJade, Sep 14 '16 at 12:14
@user2079303: right, I misread the comment about "keyboard input", I apologize. But you can poll standard input with modern c++ in a portable way — Garf365, Sep 14 '16 at 12:18

score 3 · Accepted Answer · edited May 23 '17 at 12:08

3

On Windows, this program will loop until a keyboard key is pressed :

#include <conio.h>

void main()
{
    while (1)
    {
        if (_kbhit())
        {
            break;
        }
    }
}

On linux, have a look at this answer. It tells you how to use ncurses to do what you want.

edited May 23 '17 at 12:08

Community

1
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answered Sep 14 '16 at 12:12

V. Semeria

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2

Why not `while(!_kbhit()) {/*do stuff*/}` ? – GreenAsJade Sep 14 '16 at 12:16
3

it doesn't really matter either way since OP is on Linux and not Windows – Rok Sep 14 '16 at 12:17
Link to a linux answer added above. – V. Semeria Sep 14 '16 at 12:32
@V.Semeria a link isn't good enough, it isn't an answer unless it actually contains the relevant information. – Mark Ransom Sep 14 '16 at 13:51
It contains an example of ncurses that solves the question. – V. Semeria Sep 14 '16 at 15:22

How to collect keyboard input inside a loop in c++

1 Answers1