C++: execute a while loop until a key is pressed e.g. Esc?

Question

Does anyone have a snippet of code that doesn't use windows.h to check for a key press within a while loop. Basically this code but without having to use windows.h to do it. I want to use it on Linux and Windows.

#include <windows.h>
#include <iostream>

int main()
{
    bool exit = false;

    while(exit == false)
    {
        if (GetAsyncKeyState(VK_ESCAPE))
        {
            exit = true;
        }
        std::cout<<"press esc to exit! "<<std::endl;
    }

    std::cout<<"exited: "<<std::endl;

    return 0;
}

`s/GetAsyncKeyState(VK_ESCAPE)/GetAsyncKeyState(VK_ESCAPE) & 0x8000`. — chris, Apr 01 '13 at 04:11
It means you should replace the first with the second. It's specified that if the key is down, the MSB is on. Standard C++ doesn't have a portable solution for this that I know of. I suppose a multithreaded `cin.get()` kind of works, but I'm very iffy with doing that. — chris, Apr 01 '13 at 04:13
I believe that this post might be duplicate of [this one][1]. [1]: http://stackoverflow.com/questions/421860/c-c-capture-characters-from-standard-input-without-waiting-for-enter-to-be-pr# — Kupto, Apr 01 '13 at 04:31
@Kupto No because they didn't ask for this to be multi-platform. Check out the answer. Its similar but I wanted this to work on windows and linux. Believe me I searched all over google before asking this. — pandoragami, Apr 01 '13 at 04:35

score 8 · Answer 1 · answered Apr 01 '13 at 04:26

8

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

int main()
{
    char c;
    std::cout<<"press esc to exit! "<<std::endl;
    while(true)
    {
        c=getch();
        if (c==27)
          break;
    }

    std::cout<<"exited: "<<std::endl;

    return 0;
}

answered Apr 01 '13 at 04:26

Nasir Mahmood

1,445
1
13
18

So `getch()` just returns `EOF` with no input? Isn't `getchar()` more portable? – Baldrickk Sep 22 '14 at 13:23

score 2 · Accepted Answer · answered Apr 01 '13 at 04:23

2

Your best bet is to create a custom "GetAsyncKeyState" function that will use #IFDEF for windows and linux to choose the appropriate GetAsyncKeyState() or equivalent.

No other way exists to achieve the desired result, the cin approach has its problems - such as the application must be in focus.

answered Apr 01 '13 at 04:23

Thats what I thought too. I don't like using `#ifdef _WIN32 #endif #ifdef linux #endif` but theres no other way I guess. – pandoragami Apr 01 '13 at 04:24
1

Another solution would be to have the implementation of such a function in two files, implement_linux.cpp and implement_windows.cpp for example, and simply compile and link with one of them depending on the system you're using. No #ifdef needed ! – Nbr44 Apr 01 '13 at 04:26

score 1 · Answer 3 · answered Apr 01 '13 at 04:14

1

char c;
while (cin >> c) {
...
}

ctrl-D terminates the above loop. It will continue so long as a char is entered.

answered Apr 01 '13 at 04:14

gongzhitaao

6,566
3
36
44

I'm on windows XP right now. Tried it and it just hangs. I guess its normal. – pandoragami Apr 01 '13 at 04:17
@lost_with_coding, Yes, all input in standard C++ is blocking. I'm not particularly confident in hacks to change that behaviour. – chris Apr 01 '13 at 04:17
@chris So there is no way to do this on windows without `windows.h`? – pandoragami Apr 01 '13 at 04:18
@lost_with_coding sorry for the misleading, windows does not have an equivalent key to ``ctrl-d``. – gongzhitaao Apr 01 '13 at 04:19
I guess I could do `#ifdef _WIN32 #endif #ifdef linux #endif` – pandoragami Apr 01 '13 at 04:23
@lost_with_coding The function ``kbhit()`` in this post might be of some help: http://stackoverflow.com/questions/1449324/how-to-simulate-press-any-key-to-continue – gongzhitaao Apr 01 '13 at 04:34

AmmAr · Answer 4 · 2015-10-11T17:17:18.443

-1

//simplest.

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

using namespace std;
    int main()
    {

        char ch;
        bool loop=false;

      while(loop==false)
       {
        cout<<"press escape to end loop"<<endl;
        ch=getch();
        if(ch==27)
        loop=true;
       }
        cout<<"loop terminated"<<endl;
        return 0;
    }

edited Oct 11 '15 at 17:17

answered Oct 11 '15 at 17:11

AmmAr

1
1

score -2 · Answer 5 · answered Jun 17 '16 at 18:45

//its not the best but it works


#include <vector>
#define WINVER 0x0500
#include <windows.h>
#include <conio.h>
#include <iostream>

int main()
{
char c;
std::cout<<"press esc to exit! "<<std::endl;
while(true)
{

std::cout<<"executing code! , if code stops press any key to     continue or esc to stop"<<std::endl;


 INPUT ip;

// Set up a generic keyboard event.aa
ip.type = INPUT_KEYBOARD;
ip.ki.wScan = 0; // hardware scan code for key
ip.ki.time = 0;
ip.ki.dwExtraInfo = 0;

int lol =   65; //a key
    // Press the "A" key
ip.ki.wVk = lol; // virtual-key code for the "a" key
ip.ki.dwFlags = 0; // 0 for key press
SendInput(1, &ip, sizeof(INPUT));

// Release the "A" key
ip.ki.dwFlags = KEYEVENTF_KEYUP; // KEYEVENTF_KEYUP for key release
SendInput(1, &ip, sizeof(INPUT));

    c=getch();
    if (c==27)
      break;
  }

std::cout<<"exited: "<<std::endl;
return 0;
}

Please do not post the same answer to multiple questions. If the same information really answers both questions, then one question (usually the newer one) should be closed as a duplicate of the other. You can indicate this by [voting to close it as a duplicate](http://stackoverflow.com/help/privileges/close-questions) or, if you don't have enough reputation for that, [raise a flag](http://stackoverflow.com/help/privileges/flag-posts) to indicate that it's a duplicate. Otherwise, be sure you tailor your answer to *this* question and don't just paste the same answer in multiple places. — elixenide, Jun 17 '16 at 19:07

C++: execute a while loop until a key is pressed e.g. Esc?

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