如何将getpass（）与poll（）一起使用来设置时间限制？

Question

I am using poll() along with getpass() to get input from user in limited time. It works, but instead of showing message given in getpass() , it doesn't shows message until pressing enter key . How can I use these two functions together so that message given in getpass() will be displayed without need to enter enter key , and time to enter password will be limited?

I tried to solve this by clearing stdin and stdout , but it did't work.

#include <poll.h>
struct pollfd mypoll = { STDIN_FILENO, POLLIN|POLLPRI };
if( poll(&mypoll, 1, 20000) )
{
    char *pass = getpass("\nPlease enter password:");
}

Answer 1

getpass function is obsolete. Do not use it.

Here is the working example. The program wait for 20 seconds. If user enters password in 20 seconds then program reads information to password otherwise inform user about time exceeded to enter password.The following example does not tunoff echo.

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

int main()
{
    struct pollfd mypoll = { STDIN_FILENO, POLLIN|POLLPRI };
    char password[100];

    printf("Please enter password\n");
    if( poll(&mypoll, 1, 20000) )
    {
        scanf("%99s", password); 
        printf("password - %s\n", password);
    }
    else
    {
        puts("Time Up");
    }

    return 0;
}

The following example will turnoff echo. Works same as getpass. This works on linux/macosx, a windows version should use Get/Set ConsoleMode

#include <unistd.h>
#include <poll.h>
#include <stdio.h>
#include <termios.h>
#include <stdlib.h>
int main()
{
    struct pollfd mypoll = { STDIN_FILENO, POLLIN|POLLPRI };
    char password[100];
    struct termios oflags, nflags;

    /* disabling echo */
    tcgetattr(fileno(stdin), &oflags);
    nflags = oflags;
    nflags.c_lflag &= ~ECHO;
    nflags.c_lflag |= ECHONL;

    if (tcsetattr(fileno(stdin), TCSANOW, &nflags) != 0) {
        perror("tcsetattr");
        return EXIT_FAILURE;
    }

    printf("Please enter password\n");
    if( poll(&mypoll, 1, 20000) )
    {
        scanf("%s", password);
        printf("password - %s\n", password);
    }
    else
    {
        puts("Time Up");
    }

    /* restore terminal */
    if (tcsetattr(fileno(stdin), TCSANOW, &oflags) != 0) {
        perror("tcsetattr");
        return EXIT_FAILURE;
    }
    return 0;
}