How to flush cin including all occurrences of newline

My app first takes some input, then it 'thinks' showing a progress bar, then throws an exit code and waits with getchar() for ENTER to be clicked before exiting.

The problem is that if I click ENTER during the 'thinking' process, it will affect the getchar(), causing it to exit immediately after throwing the exit code, without waiting for a new ENTER. I only found methods of clearing the cin buffer until \n what doesn't work in my case - I need to somehow clear the whole buffer just before calling getchar() - I think.

My app is meant for both Windows and MacOS, but in different #ifdefs, so both cases need solving.

The code is similar to this:

int main()
{
    string name;
    getline(cin, name);
    //Think and show progres bar
    cout << "Ended with exit code 1";
    getchar();
    return 1;
}

Solution

Here you go.

On Windows, you can use _kbhit/_getch from conio.h.

On POSIX-compliant systems, such as MacOS, you can use termios.h to reproduce those functions.

// You didn't include those three lines in your sample code, but they're implied, so here they are.
#include <iostream>
#include <string>
use namespace std;

// kbhit/getch compatibility

#if defined(_WIN32) || defined(WIN32)

#include <conio.h>

#define kbhit _kbhit
#define getch _getch

#elif defined (__unix__) || (defined (__APPLE__) && defined (__MACH__)) // Should work for any POSIX-compliant system, including MacOS

#include <sys/ioctl.h>
#include <sys/select.h>
#include <termios.h>
#include <stdarg.h>
#include <unistd.h>

static int peek = -1;
inline int kbhit() {
    // Initial variables
    char ch;
    int nread;
    struct termios origTerm, newTerm;

    // Check if a character hasn't been buffered yet
    if (peek != -1)
        return 1;

    // Preparing the terminal
    tcgetattr(0, &origTerm);
    newTerm = origTerm;
    newTerm.c_lflag &= ~ICANON;
    newTerm.c_lflag &= ~ECHO;
    newTerm.c_lflag &= ~ISIG;
    newTerm.c_cc[VMIN] = 1;
    newTerm.c_cc[VTIME] = 0;
    tcsetattr(0, TCSANOW, &newTerm);

    // Read potential keyboard input
    newTerm.c_cc[VMIN] = 0;
    tcsetattr(0, TCSANOW, &newTerm);
    nread = read(0, &ch, 1);
    newTerm.c_cc[VMIN] = 1;
    tcsetattr(0, TCSANOW, &newTerm);

    // Restore the terminal
    tcsetattr(0, TCSANOW, &origTerm);

    // Check if something was read
    if (nread == 1) {
        peek = ch;
        return 1;
    }
    return 0;
}

inline char getch() {
    char ch = peek;
    peek = -1;
    return ch;
}

#else

#error kbhit and getch are not supported.

#endif

// Your code, with a new line to clear the keyboard buffer

int main()
{
    string name;
    getline(cin, name);

    //Think and show progress bar

    while (kbhit()) getch(); // Clear keyboard buffer

    cout << "Ended with exit code 1";
    getchar();
    return 1;
}

References: