Flushing stdin doesn't seem to work

[lazka]

This is an example extracted from pacman https://gitlab.archlinux.org/pacman/pacman/-/blob/2180e4d127af2ce0722b831a7131283604a7bdf1/src/pacman/util.c#L185

pacman flushes stdin before asking a question and doesn't have and takes any non-"y" as not, leading to user confusion if for example enter is pressed during the waiting before the question is asked, leading to surprise aborts of the process, example: msys2/MSYS2-packages#3532

This example allows you to input text, then flushes as pacman does, then reads stdin. Flushing currently doesn't have an effect.

#include <stdio.h>
#include <unistd.h>
#include <termios.h>

int main() {
    printf("type something in the next 5 secs\n");
    for (int i; i < 5; i++) {
        sleep(1);
        printf("%d\n", i);
    }

    // Flush stdin
    int fd = fileno(stdin);
    if (fd != -1) {
        printf("flushing stdin\n");
        if (tcflush(fd, TCIFLUSH) == -1) {  // this doesn't seem to do anything
            perror("Error flushing stdin");
            return 1;
        }
    } else {
        perror("Error getting file descriptor for stdin");
        return 1;
    }

    char buffer[100];
    printf("Enter some text:\n");
    fgets(buffer, sizeof(buffer), stdin);
    printf("You entered: %s\n", buffer);

    return 0;
}

[lazka]

Confirmed also with cygwin.

It happens with mintty, but not when running in Windows Terminal. Disabling conpty doesn't make a difference.

The question now is if this is a mintty or cygwin issue.

edit: the issue also exists with xterm under cygwin

edit: the issue doesn't exist with cmd.exe

[lazka]

on IRC it was pointed out that the issue existing in xterm might indicate that it's a cygwin problem

[lazka]

next: ask on the cygwin ML for help