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{{task|Keyboard input}} [[Category:Hardware]] [[Category:Terminal control]] [[Category:Simple]] [[user input::task| ]] {{omit from|ACL2}} {{omit from|GUISS}} {{omit from|PARI/GP}}
Flush the [[input device::keyboard]] buffer.
This reads characters from the keyboard input and discards them until there are no more currently buffered, and then allows the program to continue.
''The program must not wait for users to type anything.''
Ada
with Ada.Text_IO;
procedure Flushtest is
use Text_IO;
begin
Put_Line ("Type anything for 2 s");
delay 2.0;
Flush_Input:
declare
Ch : Character;
More : Boolean;
begin
loop
Get_Immediate (Ch, More);
exit when not More;
end loop;
end Flush_Input;
New_Line;
Put_Line ("Okay, thanks. Here is some input from you:");
Put_Line (Get_Line);
end Flushtest;
Axe
While getKey(0)
End
BASIC
=
Applesoft BASIC
=
10 IF PEEK (49152) > 127 THEN C = PEEK (49168): GOTO 10
=
Locomotive Basic
=
(Only available in BASIC 1.1 though, i.e. not on the CPC 464.)
=
## ZX Spectrum Basic
=
There is no need to flush keyboard buffer in Spectrum since key presses are not buffered.
If a key is currently pressed, the following waits until key is released.
```basic
10 IF INKEY$ <> "" THEN GO TO 10
BBC BASIC
*FX 15,1
Strictly speaking *FX 15,1 is an Operating System command, but it is emulated in BBC BASIC for Windows. Alternatively the keyboard buffer may be flushed as follows:
REPEAT UNTIL INKEY(0)=-1
C
{{libheader|POSIX}} Code lifted from [[Keyboard input/Obtain a Y or N response]]:
#include <stdio.h>
#include <stdio.h>
#include <termios.h>
#include <unistd.h>
#include <fcntl.h>
#include <ctype.h>
void set_mode(int want_key)
{
static struct termios old, new;
if (!want_key) {
tcsetattr(STDIN_FILENO, TCSANOW, &old);
return;
}
tcgetattr(STDIN_FILENO, &old);
new = old;
new.c_lflag &= ~(ICANON);
tcsetattr(STDIN_FILENO, TCSANOW, &new);
}
int get_key()
{
int c = 0;
fd_set fs;
FD_ZERO(&fs);
FD_SET(STDIN_FILENO, &fs);
select(STDIN_FILENO + 1, &fs, 0, 0, 0);
if (FD_ISSET(STDIN_FILENO, &fs)) {
c = getchar();
set_mode(0);
}
return c;
}
int main()
{
int c = 0;
while (c != 'n') {
set_mode(1);
/* flush pending input so we won't format the hardrive
because user accidentally typed 'y' before we even prompted */
tcflush(STDIN_FILENO, TCIFLUSH);
printf("Show this prompt again [Yes/No/Ignore you]? ");
fflush(stdout);
switch(c = tolower(get_key())) {
case 'y': putchar('\n');
break;
case 'n': printf("\nDone\n");
break;
case 'i': puts("\nI'll ignore keys for 5 seconds");
sleep(5);
putchar('\n');
break;
default:
puts("\nAssume that was the cat.");
}
}
return 0;
}
D
extern (C) {
void _STI_conio();
void _STD_conio();
int kbhit();
int getch();
}
void main() {
void flushKB() {
while (kbhit()) getch();
}
_STI_conio();
flushKB();
_STD_conio();
}
DCL
{{out}}
```txt
$ @flush_the_keyboard_buffer ! ignores/discards keystrokes for 10 seconds
$
ERRE
!$KEY
..........
REPEAT
GET(K$)
UNTIL K$=""
..........
Note: Test after K$ can be replaced with LEN(K$)=0.
Euphoria
while get_key()!=-1 do
end while
Go
{{libheader|Curses}}
package main
import (
"log"
gc "code.google.com/p/goncurses"
)
func main() {
_, err := gc.Init()
if err != nil {
log.Fatal("init:", err)
}
defer gc.End()
gc.FlushInput()
}
FreeBASIC
' FB 1.05.0 Win64
' Get characters from the keyboard buffer until there are none left
While Inkey <> "" : Wend
Print "Keyboard buffer flushed"
Sleep
Haskell
This relies upon POSIX terminal support.
import Control.Concurrent (threadDelay)
import Control.Monad (when)
import System.IO (hFlush, stdout)
import System.Posix
-- If the file descriptor is associated with a terminal, then flush its input,
-- otherwise do nothing.
termFlush :: Fd -> IO ()
termFlush fd = do
isTerm <- queryTerminal fd
when isTerm $ discardData fd InputQueue
main :: IO ()
main = do
putStrLn "Type some stuff...\n"
threadDelay $ 3 * 1000000
putStrLn "\n\nOk, stop typing!\n"
threadDelay $ 2 * 1000000
termFlush stdInput
putStr "\n\nType a line of text, ending with a newline: "
hFlush stdout
line <- getLine
putStrLn $ "You typed: " ++ line
termFlush stdInput
i
There is no need to manually flush the keyboard buffer in 'i', the only way to receive keyboard input is in graphics mode and keyboard input is automatically flushed every update.
=={{header|Icon}} and {{header|Unicon}}== The following solution works in both Icon and Unicon.
procedure flushKB()
while kbhit() do getch() # flush input
end
Julia
{{libheader|Gtk}}
using Gtk
function flush_keyboard()
win = GtkWindow("", 1, 1)
keyget(w, event) = Int32(0)
signal_connect(keyget, win, "key-press-event")
visible(win, false)
sleep(0.25)
end
Kotlin
There appears to be no completely satisfactory, platform independent, way in Java (and hence in the JVM-targetted version of Kotlin) to flush the keyboard buffer. The method presented here may not always work (as the InputStream.available method only gives an estimate of the bytes in the buffer) but is better than nothing and does not block as other approaches to the problem may do.
// version 1.0.6
fun main(args: Array<String>) {
while (System.`in`.available() > 0) System.`in`.read()
println("Goodbye!")
}
M2000 Interpreter
M2000 run in M2000 Environment so has total control, including keyboard. Here we read keyboard from console (we can't read with this way for froms, we have to read from events).
Inkey$ return "" if not key pressed, or the key. Return unicode char
Key$ wait for key, to press, we can use Keyboard to send keys
inkey(1000) wait for a new key to press, we can't use Keyboard to send keys, there is no auto repeat, so if we have a second read inkey(1000) and we keep press the same key, nothing happen (return -1, as no new key)
Keypress(32) we can read if a space key is now pressed. Can't read keyboard if m2000 environment application hasn't focus. It's not a key logger. Keypress(1) read left mouse button, Keypress(2) read right mouse button.
Module Checkit {
\\ feed keyboard
Keyboard "abcd"
\\ Work in Windows not in Linux (no Osk.exe exist)
\\ no error return in linux
Keyboard ! 'open virtual keyboard
Wait 3000
\\ flush keyboard
\\ we can use Do or Repeat (is the same)
Repeat {
a$=inkey$
if a$="" then Print :exit
Print a$;
} Always
}
Checkit
This isn't the task. Input ends when statement Input End occur, in a thread.
Statement After make a thread for one time only. When in Input interpreter wait for A$ to input, threads allowed to run. If we write but forget to press enter then input flush. If no input statement run then nothing happen when Input End run.
Module checkit {
Print "You have 3 seconds to write your name (press enter)"
After 3000 {
Input End
}
Input "Your name:", A$
If A$="" Then Print "Not Ready" : Exit
Print "Ok:";A$
}
Checkit
Nim
{{libheader|POSIX}}
const TCIFLUSH: cint = 0
proc tcflush(fd, queue_selector: cint): cint {.header: "termios.h".}
discard tcflush(cint(getFileHandle(stdin)), TCIFLUSH)
Oforth
import: console
System.Console flush
Perl
use Term::ReadKey;
ReadMode 'restore'; # Flush the keyboard and returns input stream to initial state
# ReadMode 0; # Numerical equivalent of keyboard restore (move comment marker to use instead)
# A more complete example for use in keyboard handler programming.
# We should also check we are being used in an interactive context (not done here).
use Term::ReadKey;
ReadMode 'cbreak';
# Flush the keyboard in terminal character break mode
while (defined ReadKey -1) {
# Do nothing
}
# Don't forget to restore the readmode, when we are finished using the keyboard
ReadMode 'restore';
Perl 6
{{works with|Rakudo|2018.12}} Using termios to set some input attributes, flush the buffer & do unbuffered reads. Longer than strictly necessary to demonstrate concepts and make it easy to verify that it actually works as advertised.
use Term::termios;
constant $saved = Term::termios.new( :fd($*IN.native-descriptor) ).getattr;
constant $termios = Term::termios.new( :fd($*IN.native-descriptor) ).getattr;
# set some modified input flags
$termios.unset_iflags(<BRKINT ICRNL ISTRIP IXON>);
$termios.unset_lflags(< ECHO ICANON IEXTEN>);
$termios.setattr(:DRAIN);
# reset terminal to original settings on exit
END { $saved.setattr(:NOW) }
# Sleep for a few seconds to give you time to fill the input buffer,
# type a bunch of random characters.
sleep 2;
# ------- The actual task --------
# Flush the input buffer
$termios.setattr(:FLUSH);
# --------------------------------
# Ctrl-C to exit
loop {
# Read up to 5 bytes from STDIN
# F5 through F12 are 5 bytes each
my $keypress = $*IN.read: 5;
# print the ordinals of the keypress character
print $keypress.decode.ords;
print "|";
}
Phix
while get_key()!=-1 do end while
PicoLisp
(while (key 10))
PowerShell
The following uses the special $Host variable which points to an instance of the PowerShell host application. Since the host's capabilities may vary this may not work in all PowerShell hosts. In particular, this works in the console host, but not in the PowerShell ISE.
while ($Host.UI.RawUI.KeyAvailable) {
$Host.UI.RawUI.ReadKey() | Out-Null
}
To flush the keyboard buffer use:
$Host.UI.RawUI.FlushInputBuffer()
PureBasic
While Inkey(): Wend
Python
def flush_input():
try:
import msvcrt
while msvcrt.kbhit():
msvcrt.getch()
except ImportError:
import sys, termios
termios.tcflush(sys.stdin, termios.TCIOFLUSH)
Racket
Using stty to get the terminal into raw mode.
#lang racket
(define-syntax-rule (with-raw body ...)
(let ([saved #f])
(define (stty x) (system (~a "stty " x)) (void))
(dynamic-wind (λ() (set! saved (with-output-to-string (λ() (stty "-g"))))
(stty "raw -echo opost"))
(λ() body ...)
(λ() (stty saved)))))
(with-raw
(printf "Keys pressed from now will be ignored\n")
(sleep 2)
(let loop () (when (char-ready?) (read-char) (loop))) ; flush input
(printf "Now press a key which will not be ignored\n")
(printf "You pressed ~a\n" (read-char)))
REXX
This will work for Regina:
This will work for CMS REXX, PC/REXX, Personal REXX, and TSO REXX:
```rexx
'DROPBUF'
Ring
# Project: Keyboard input/Flush the keyboard buffer
Fflush(stdin)
Ruby
Each terminal device has an ''input queue'' for keyboard input. We can either flush this input queue, or read it empty.
Ruby 1.9.3 adds a new library 'io/console', providing IO#iflush to flush and discard the input queue. If its IO object is not a terminal, it raises an error, perhaps Errno::ENODEV.
{{works with|Ruby|1.9.3}}
require 'io/console'
$stdin.iflush
The other option uses IO#read_nonblock to read the input, without any blocking or waiting. This has a caveat: if the terminal uses the ''canonical input mode'', IO reads only entire lines; and if the input queue contains part of a line, IO#read_nonblock cannot discard this last partial line!
loop { $stdin.read_nonblock(256) } rescue nil
The complete solution calls IO#iflush, or turns off canonical input mode and calls IO#read_nonblock.
class IO
def discard_input
icanon = false
if tty?
begin
# With Ruby 1.9.3, simply call IO#iflush.
require 'io/console'
return iflush
rescue LoadError
# Try to run stty(1) to check if this terminal uses
# canonical input mode. Acts like `stty -a`, but redirects
# stdin from tty. Works with Ruby 1.8, no Process#spawn.
r, w, pid = nil
begin
r, w = IO.pipe
pid = fork do
IO.for_fd(0).reopen(self) # stdin from tty
IO.for_fd(1).reopen(w) # stdout to pipe
exec 'stty', '-a'
end
w.close; w = nil
icanon = (not r.read.include? "-icanon")
rescue
# stty(1) only works with Unix clones.
ensure
pid and Process.wait pid
w and w.close
r and r.close
end
end
end
if icanon
# Turn off canonical input mode.
pid = nil
begin
pid = fork do
IO.for_fd(0).reopen(self) # stdin from tty
exec 'stty', '-icanon'
end
ensure
pid and Process.wait pid
end
end
# Discard input.
loop { $stdin.read_nonblock(256) } rescue nil
if icanon
# Turn on canonical input mode.
pid = nil
begin
pid = fork do
IO.for_fd(0).reopen(self) # stdin from tty
exec 'stty', 'icanon'
end
ensure
pid and Process.wait pid
end
end
nil
end
end
# Demonstration: discard input, then input a line from user.
puts 'Type anything for 2 seconds.'
sleep 2
$stdin.discard_input
print 'Enter a line? '
if line = $stdin.gets
then print 'Got line. ', line
else puts 'No line!'
end
Scala
def flush() { out.flush() }
Seed7
The Seed7 library [http://seed7.sourceforge.net/libraries/keybd.htm keybd.s7i] defines the file [http://seed7.sourceforge.net/manual/file.htm#Keyboard_file KEYBOARD], which provides functions like [http://seed7.sourceforge.net/libraries/keybd.htm#keypressed%28in_keyboard_file%29 keypressed] and [http://seed7.sourceforge.net/libraries/keybd.htm#getc%28in_console_keybd_file%29 getc].
while keypressed(KEYBOARD) do
ignore(getc(KEYBOARD));
end while;
Sidef
{{trans|Perl}}
var k = frequire('Term::ReadKey');
k.ReadMode('restore'); # Flush the keyboard and returns input stream to initial state
# ReadMode 0; # Numerical equivalent of keyboard restore (move comment marker to use instead)
# A more complete example for use in keyboard handler programming.
# We should also check we are being used in an interactive context (not done here).
k.ReadMode('cbreak');
# Flush the keyboard in terminal character break mode
while (k.ReadKey(-1) != nil) {
# Do nothing
}
# Don't forget to restore the readmode, when we are finished using the keyboard
k.ReadMode('restore');
Tcl
# No waiting for input
fconfigure stdin -blocking 0
# Drain the data by not saving it anywhere
read stdin
# Flip back into blocking mode (if necessary)
fconfigure stdin -blocking 1
Vedit macro language
Key_Purge()
XPL0
code OpenI=13;
OpenI(0)