Very Computer

Thanks!

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Before you buy.

#include <poll.h>

int main ( void ){
   int pollStatus = -1;
   struct pollfd inputStream [1];
   char c;

   inputStream [0].events = POLLRDNORM;
   inputStream [0].revents = 0;
   inputStream [0].fd = 0;

   while ( 1 ){
       pollStatus = poll (inputStream, 1, 0);
       if (pollStatus == -1) exit ( -1 );
       if (pollStatus){
           read (0, &c, 1);
           write (1, &c, 1);
           inputStream [0].revents = 0;
       }
   }  
   exit ( 0 );

Quote:}

#> I'm a bit of a newbie in this, so this could be a stupid
#> question.  I'm writing a program (in C) that needs to
#> check to see if the user typed a character to the screen,
#> without waiting for that character if it isn't there.
#> So, while I'm doing a bunch of stuff in a while(1) type
#> of loop, the user could type 'q' to the screen, and at
#> a certain spot in the loop, the program would check to
#> see if the user typed 'q'.  If the user didn't type anything,
#> I would want it to continue on as if nothing happened.
#> Is this possible?  I was told to mess around with the termios
#> settings, but I haven't figured it out yet.
#
#Use select or poll on the input file descriptor.
#
#

 Miguel>    inputStream [0].events = POLLRDNORM;
 Miguel>    inputStream [0].revents = 0;
 Miguel>    inputStream [0].fd = 0;

 Miguel>    while ( 1 ){
 Miguel>        pollStatus = poll (inputStream, 1, 0);
 [...]
 Miguel> This avoids using a blocking READ statement. The user will
 Miguel> still have to hit ENTER to enter input of any size.

The user will still have to hit ENTER in order for poll() to return
that input is ready, unless you also take the terminal out of
canonical input mode. see FAQ.

--
Andrew.

comp.unix.programmer FAQ: see <URL: http://www.erlenstar.demon.co.uk/unix/>
                           or <URL: http://www.whitefang.com/unix/>

3.2 How can I read single characters from the terminal?
 =======================================================

     How can I read single characters from the terminal? My program is
 always waiting for the user to press `<RETURN>'.

 Terminals are usually in canonical mode, where input is read in lines
after it is edited. You may set this into non-canonical mode, where you
set how many characters should be read before
 input is given to your program. You also may set the timer in
non-canonical mode terminals to 0, this timer flushs your buffer at set
intervals. By doing this, you can use `getc()' to grab the
 key pressed immediately by the user. We use `tcgetattr()' and
`tcsetattr()' both of which are defined by POSIX to manipulate the
`termios' structure.

     #include <stdlib.h>
     #include <stdio.h>

     #include <termios.h>
     #include <string.h>

     static struct termios stored_settings;

     void set_keypress(void)
     {
         struct termios new_settings;

         tcgetattr(0,&stored_settings);

         new_settings = stored_settings;

         /* Disable canonical mode, and set buffer size to 1 byte */
   new_settings.c_lflag &= (~ICANON);
         new_settings.c_cc[VTIME] = 0;
         new_settings.c_cc[VMIN] = 1;

         tcsetattr(0,TCSANOW,&new_settings);
         return;
     }

     void reset_keypress(void)
     {
         tcsetattr(0,TCSANOW,&stored_settings);
         return;
     }

 3.3 How can I check and see if a key was pressed?
 =================================================

     How can I check and see if a key was pressed? On DOS I use the
`kbhit()' function, but there doesn't seem to be an equivalent?

 If you set the terminal to single-character mode (see previous answer),
then (on most systems) you can use `select()' or `poll()' to test for
readability.

--