Non Blocking Keyboard Input (C++)

kbNonblock.c

#include <termios.h>
#include <stdlib.h>

void RestoreKeyboardBlocking(struct termios *initial_settings)
{
	tcsetattr(0, TCSANOW, initial_settings);
}

void SetKeyboardNonBlock(struct termios *initial_settings)
{

    struct termios new_settings;
    tcgetattr(0,initial_settings);

    new_settings = initial_settings;
    new_settings.c_lflag &= ~ICANON;
    new_settings.c_lflag &= ~ECHO;
    new_settings.c_lflag &= ~ISIG;
    new_settings.c_cc[VMIN] = 0;
    new_settings.c_cc[VTIME] = 0;

    tcsetattr(0, TCSANOW, &new_settings);
}

int main()
{
    struct termios term_settings;
    char c = 0;

    SetKeyboardNonBlock(&term_settings);

    while(c != 'Q')
    {
        c = getchar();
        if(c > 0)
            printf("Read: %c\n", c);
    }

    //Not restoring the keyboard settings causes the input from the terminal to not work right
    RestoreKeyboardBlocking(&term_settings);

    return 0;
}

Thanks for this. I was struggling to get non blocking getchar going until I found this which got me reading the c_cc[VMIN] and c_cc[VTIME] in the termios docs. Here are the extra steps I had to take to get a working solution:

Line 15, change to
new_settings = *initial_settings;
to avoid compiler error

error: no match for 'operator=' (operand types are 'termios' and 'termios*')

That got it to compile and I notice getchar isn't blocking now, which is good, but with just two small problems. getchar always returns EOF and doesn't pull any characters from the input buffer :-)

The termios documentation doesn't mention getchar, it talks about its affect on read() so I replaced getchar with

char getcharAlt() {
    char buff[2];
    int l = read(STDIN_FILENO,buff,1);
    if (l>0) return buff[0];
    return ( EOF);
}

and have a solution for my Raspberry Pi running Raspbian Buster.