Keyboard input/Flush the keyboard buffer

From Rosetta Code
Task
Keyboard input/Flush the keyboard buffer
You are encouraged to solve this task according to the task description, using any language you may know.

Flush the   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.

6502 Assembly[edit]

Works with: [Easy6502]

On the Easy6502 and 6502asm simulators, the zero page memory address 0xFF is a memory-mapped port that reflects the ASCII code of last key you pressed on your keyboard.

Writing a value of 0 (or almost any ASCII control code that you can't type on your keyboard) to it effectively flushes the keyboard buffer. This prevents an input loop from thinking your finger is still on that key even after you stopped pressing it.

lda #$00
sta $FF

8086 Assembly[edit]

Works with: MS-DOS

Depending on the value of AL, you can have this system call "slide" into another related system call immediately after flushing the keyboard buffer. After flushing the keyboard buffer, AL will be copied into AH and then int 21h will be called again. Make sure that any other parameters needed by the interrupt you "slide into" are loaded before flushing, as you won't get a chance to do so between the flush and the second system call!

The valid values of AL for this interrupt are:

  • 0x01: Read a character from standard input with echo
  • 0x06: Direct console output
  • 0x07: Direct character input, no echo
  • 0x08: Character input without echo
  • 0x0A: Buffered input (for text strings).


If you just want to flush the keyboard buffer without doing anything else, load a zero (or any value that isn't one of the above) into AL.

mov ax,0C00h ;equivalent of "mov ah,0Ch mov al,0"
int 21h
mov ax,0C0Ah
int 21h ;flush the keyboard buffer then immediately ask the user to type in a sentence and hit Enter when done.

AArch64 Assembly[edit]

Works with: as version Raspberry Pi 3B version Buster 64 bits
/* ARM assembly AARCH64 Raspberry PI 3B */
/*  program keyboardInput64.s   */
 
/*******************************************/
/* Constantes file                         */
/*******************************************/
/* for this file see task include a file in language AArch64 assembly*/
.include "../includeConstantesARM64.inc"
.equ IOCTL,     0x1D  // Linux syscall
.equ SIGACTION, 0x86  // Linux syscall
.equ SYSPOLL,   0x16  // Linux syscall
.equ CREATPOLL, 0x14  // Linux syscall
.equ CTLPOLL,   0x15  // Linux syscall
.equ TCGETS,    0x5401
.equ TCSETS,    0x5402
.equ ICANON,    2
.equ ECHO,     10
.equ POLLIN,    1
.equ EPOLL_CTL_ADD,    1

.equ SIGINT,   2    // Issued if the user sends an interrupt signal (Ctrl + C)
.equ SIGQUIT,  3    // Issued if the user sends a quit signal (Ctrl + D)
.equ SIGTERM, 15    // Software termination signal (sent by kill by default)
.equ SIGTTOU, 22    // 

.equ BUFSIZE,   80

/*******************************************/
/* Structures                               */
/********************************************/
/* structure termios see doc linux*/
    .struct  0
term_c_iflag:                    // input modes
    .struct  term_c_iflag + 4 
term_c_oflag:                    // output modes
    .struct  term_c_oflag + 4 
term_c_cflag:                    // control modes
    .struct  term_c_cflag + 4 
term_c_lflag:                    // local modes
    .struct  term_c_lflag + 4 
term_c_cc:                       // special characters
    .struct  term_c_cc + 20      // see length if necessary 
term_fin:

/* structure sigaction see doc linux */
    .struct  0
sa_handler:
    .struct  sa_handler + 8 
sa_mask:
    .struct  sa_mask + 8 
sa_flags:
    .struct  sa_flags + 8 
sa_sigaction:
    .struct  sa_sigaction + 8 
sa_fin:

/* structure poll see doc linux */
    .struct  0
poll_event:
    .struct  poll_event + 8
poll_fd:                            //   File Descriptor
    .struct  poll_fd + 8 
poll_fin:

/*********************************/
/* Initialized data              */
/*********************************/
.data
szMessPgmOk:        .asciz "End program OK.\n"
szMessErreur:       .asciz "Error detected.\n"
szCarriageReturn:   .asciz "\n"
szMessCodeErr:      .asciz "Error code décimal :  @ \n"

/*********************************/
/* UnInitialized data            */
/*********************************/
.bss  
.align 4
iEnd:           .skip 8                          // 0 loop  1 = end loop
iTouche:        .skip BUFSIZE                    // value key pressed
stOldtio:       .skip term_fin                   // old terminal state
stCurtio:       .skip term_fin                   // current terminal state
stSigAction:    .skip sa_fin                     // area signal structure
stSigAction1:   .skip sa_fin
stSigAction2:   .skip sa_fin
stSigAction3:   .skip sa_fin
stevents:       .skip 16
sZoneConv:      .skip 24
szBuffer:       .skip BUFSIZE
/*********************************/
/*  code section                 */
/*********************************/
.text
.global main 
main:                                     // entry of program 
    bl initTerm                           // terminal init
    cmp x0,0                              // error ?
    blt 100f
    bl initPoll                           // epoll instance init
    cmp x0,0
    blt 100f
    mov x22,x0                            // save epfd
    mov x20,0                             // indice
    ldr x21,qAdrszBuffer
1:
    mov x0,x22                            // epfd
    bl waitKey
    cmp x0,0
    beq 1b                                // no ket pressed -> loop
    blt 3f                                // error ?

    bl readKey                            // read one key
    cmp x0,3                              // ctrl-C
    beq 3f
    cmp x0,113                            // saisie q (quit) ?
    beq 3f
    cmp x0,81                             // saisie Q  (Quit)?
    beq 3f
    cmp x0,0xD                            // <enter> ?
    beq 2f
    strb w0,[x21,x20]                     // store byte in buffer
    add x20,x20,1                         // increment indice
    b 1b                                  // and loop
2:                                        // display buffer
    mov x0,0                              // store 0 final
    strb w0,[x21,x20]
    mov x0,x21                            // display buffer
    bl affichageMess
    ldr x0,qAdrszCarriageReturn
    bl affichageMess
    mov x20,0
    b 1b                                  // and loop for other entry
3:
    bl restauTerm                         // terminal restaur
    ldr x0,qAdrszMessPgmOk                // display end message
    bl affichageMess
100:                                      // standard end of the program 
    mov x0,0                              // return code
    mov x8,EXIT                           // request to exit program
    svc 0                                 // perform the system call
qAdrszBuffer:             .quad szBuffer
qAdrstevents:             .quad stevents
qAdrszMessErreur:         .quad szMessErreur
qAdrszCarriageReturn:     .quad szCarriageReturn
qAdrstOldtio:             .quad stOldtio
qAdrstCurtio:             .quad stCurtio
qAdrstSigAction:          .quad stSigAction
qAdrstSigAction1:         .quad stSigAction1
qAdrszMessPgmOk:          .quad szMessPgmOk
qAdrSIG_IGN:              .quad 1
qAdriEnd:                 .quad iEnd
qAdriTouche:              .quad iTouche
/*********************************/
/* init terminal state            */
/*********************************/
initTerm:
    stp x1,lr,[sp,-16]!            // save  registers
    /* read terminal state */
    mov x0,STDIN                   // input console
    mov x1,TCGETS
    ldr x2,qAdrstOldtio
    mov x8,IOCTL                   // call system Linux
    svc 0 
    cbnz x0,98f                    // error ?

    adr x0,sighandler              // adresse routine traitement signal
    ldr x1,qAdrstSigAction         // adresse structure sigaction
    str x0,[x1,sa_handler]         // maj handler
    mov x0,SIGINT                  // signal type
    ldr x1,qAdrstSigAction
    mov x2,0
    mov x3,8
    mov x8,SIGACTION               // call system
    svc 0 

    cmp x0,0                       // error ?
    bne 98f
    mov x0,SIGQUIT
    ldr x1,qAdrstSigAction
    mov x2,0                       // NULL
    mov x8,SIGACTION               // call system 
    svc 0 
    cmp x0,0                       // error ?
    bne 98f
    mov x0,SIGTERM
    ldr x1,qAdrstSigAction
    mov x2,0                       // NULL
    mov x8,SIGACTION               // appel systeme 
    svc 0 
    cmp x0,0
    bne 98f
    //
    adr x0,qAdrSIG_IGN             // address signal igonre function
    ldr x1,qAdrstSigAction1
    str x0,[x1,sa_handler]
    mov x0,SIGTTOU                 //invalidate other process signal
    ldr x1,qAdrstSigAction1
    mov x2,0                       // NULL
    mov x8,SIGACTION               // call system 
    svc 0 
    cmp x0,0
    bne 98f
    //
    /* read terminal current state  */
    mov x0,STDIN
    mov x1,TCGETS
    ldr x2,qAdrstCurtio            // address current termio
    mov x8,IOCTL                   // call systeme 
    svc 0 
    cmp x0,0                       // error ?
    bne 98f
    mov x2,ICANON | ECHO           // no key pressed echo on display
    mvn x2,x2                      // and one key 
    ldr x1,qAdrstCurtio
    ldr x3,[x1,#term_c_lflag]
    and x3,x2,x2                   // add flags 
    str x3,[x1,#term_c_lflag]      // and store
    mov x0,STDIN                   // maj terminal current state 
    mov x1,TCSETS
    ldr x2,qAdrstCurtio
    mov x8,IOCTL                   // call system
    svc 0 
    cbz x0,100f
98:                                // error display
    ldr x1,qAdrszMessErreur        // error message
    bl   displayError
    mov x0,-1
100:
    ldp x1,lr,[sp],16              // restaur  2 registers
    ret                            // return to address lr x30
qAdrstSigAction2:    .quad stSigAction2
qAdrstSigAction3:    .quad stSigAction3
/*********************************/
/* init instance epool            */
/*********************************/
initPoll:
    stp x1,lr,[sp,-16]!            // save  registers
    ldr x0,qAdrstevents
    mov x1,STDIN                   // maj structure events
    str x1,[x0,#poll_fd]           // maj FD
    mov x1,POLLIN                  // action code
    str x1,[x0,#poll_event]
    mov x0,0
    mov x8,CREATPOLL               // create epoll instance
    svc 0
    cmp x0,0                       // error ?
    ble 98f
    mov x10,x0                     // return FD epoll instance
    mov x1,EPOLL_CTL_ADD
    mov x2,STDIN                   // Fd to we want add
    ldr x3,qAdrstevents            // structure events address
    mov x8,CTLPOLL                 // call system control epoll
    svc 0
    cmp x0,0                       // error ?
    blt 98f                       // no
    mov x0,x10                     // return FD epoll instance
    b 100f
98:                                               // error display
    ldr x1,qAdrszMessErreur                       // error message
    bl   displayError
    mov x0,-1
100:
    ldp x1,lr,[sp],16              // restaur  2 registers
    ret                            // return to address lr x30
/*********************************/
/* wait key                      */
/*********************************/
/* x0 contains FD poll    */
waitKey:
    stp x1,lr,[sp,-16]!            // save  registers
    ldr x11,qAdriTouche            // key address
    str xzr,[x11]                  // raz key
1:
    ldr x10,qAdriEnd               // if signal ctrl-c  -> end
    ldr x10,[x10]
    cbnz x10,100f

    ldr x1,qAdrstevents
    mov x2,12                      // size events
    mov x3,1                       // timeout = 1  TODO: ??
    mov x4,0
    mov x8,SYSPOLL                 // call system wait POLL
    svc 0 
    cmp x0,0                       // key pressed ?
    bge 100f
98:                                // error display
    ldr x1,qAdrszMessErreur        // error message
    bl   displayError
    mov x0,-1
100:
    ldp x1,lr,[sp],16              // restaur  2 registers
    ret                            // return to address lr x30
/*********************************/
/* read key                      */
/*********************************/
/* x0 returns key value */
readKey:
    stp x1,lr,[sp,-16]!            // save  registers
    mov x0,STDIN                   // File Descriptor
    ldr x1,qAdriTouche             // buffer address
    mov x2,BUFSIZE                 // buffer size
    mov x8,READ                    // read key
    svc #0
    cmp x0,0                       // error ?
    ble 98f
    ldr x2,qAdriTouche             // key address
    ldr x0,[x2]
    b 100f
98:                                // error display
    ldr x1,qAdrszMessErreur        // error message
    bl   displayError
100:
    ldp x1,lr,[sp],16              // restaur  2 registers
    ret                            // return to address lr x30
/*********************************/
/* restaur terminal state        */
/*********************************/
restauTerm:
    stp x1,lr,[sp,-16]!            // save  registers
    mov x0,STDIN                   // end then restaur begin state terminal
    mov x1,TCSETS
    ldr x2,qAdrstOldtio
    mov x8,IOCTL                   // call system  
    svc 0
    cbz x0,100f
    ldr x1,qAdrszMessErreur        // error message
    bl   displayError
100:
    ldp x1,lr,[sp],16              // restaur  2 registers
    ret                            // return to address lr x30

/******************************************************************/
/*     signal processing                                     */ 
/******************************************************************/
sighandler:
    stp x1,lr,[sp,-16]!            // save  registers
    ldr x0,qAdriEnd
    mov x1,#1                      // maj zone end
    str x1,[x0]
    ldp x1,lr,[sp],16              // restaur  2 registers
    ret                            // return to address lr x30
/******************************************************************/
/*     display error message                                      */ 
/******************************************************************/
/* x0 contains error code */
/* x1 contains address error message    */
displayError:
    stp x2,lr,[sp,-16]!            // save  registers
    mov x2,x0                      // save error code
    mov x0,x1                      // display message error
    bl affichageMess
    mov x0,x2
    ldr x1,qAdrsZoneConv           // conversion error code
    bl conversion10S               // decimal conversion
    ldr x0,qAdrszMessCodeErr
    ldr x1,qAdrsZoneConv
    bl strInsertAtCharInc          // insert result at @ character
    bl affichageMess               // display message final
    ldp x2,lr,[sp],16              // restaur  2 registers
    ret                            // return to address lr x30
qAdrsZoneConv:        .quad sZoneConv
qAdrszMessCodeErr:    .quad szMessCodeErr
/********************************************************/
/*        File Include fonctions                        */
/********************************************************/
/* for this file see task include a file in language AArch64 assembly */
.include "../includeARM64.inc"
Output:
abcdefg
help
kk
End program OK.

Action![edit]

PROC Wait(BYTE frames)
  BYTE RTCLOK=$14
  frames==+RTCLOK
  WHILE frames#RTCLOK DO OD
RETURN

PROC Main()
  BYTE CH=$02FC ;Internal hardware value for last key pressed

  PrintE("Program is halted for 200 frames.")
  PrintE("Type character to fill the buffer.")
  Wait(200)
  PutE()

  DO
    IF CH=$FF THEN
      PrintE("The buffer is empty.")
      EXIT
    ELSE
      PrintF("The buffer stores internal key: %B.%E",CH)
      PrintE("Flush the buffer.")
      CH=$FF
    FI
  OD
RETURN
Output:

Screenshot from Atari 8-bit computer

Program is halted for 200 frames.
Type character to fill the buffer.

The buffer stores internal key: 63.
Flush the buffer.
The buffer is empty.

Ada[edit]

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;

ARM Assembly[edit]

Works with: as version Raspberry Pi
/* Programme assembleur ARM Raspberry */
/* modèle B 512MO   */
 
/* REMARK 1 : this program use routines in a include file 
   see task Include a file language arm assembly 
   for the routine affichageMess conversion10 
   see at end of this program the instruction include */

/************************************/
/* Constantes                       */
/************************************/
.equ STDIN,     0     @ Linux input console
.equ STDOUT,    1     @ Linux output console
.equ EXIT,      1     @ Linux syscall
.equ READ,      3     @ Linux syscall
.equ WRITE,     4     @ Linux syscall
.equ IOCTL,     0x36  @ Linux syscall
.equ SIGACTION, 0x43  @ Linux syscall
.equ SYSPOLL,   0xA8  @ Linux syscall

.equ TCGETS,    0x5401
.equ TCSETS,    0x5402
.equ ICANON,    2
.equ ECHO,     10
.equ POLLIN,    1

.equ SIGINT,   2    @ Issued if the user sends an interrupt signal (Ctrl + C)
.equ SIGQUIT,  3    @ Issued if the user sends a quit signal (Ctrl + D)
.equ SIGTERM, 15    @ Software termination signal (sent by kill by default)
.equ SIGTTOU, 22    @ 

.equ BUFSIZE,   80


/*******************************************/
/* Structures                               */
/********************************************/
/* structure termios see doc linux*/
    .struct  0
term_c_iflag:                    @ input modes
    .struct  term_c_iflag + 4 
term_c_oflag:                    @ output modes
    .struct  term_c_oflag + 4 
term_c_cflag:                    @ control modes
    .struct  term_c_cflag + 4 
term_c_lflag:                    @ local modes
    .struct  term_c_lflag + 4 
term_c_cc:                       @ special characters
    .struct  term_c_cc + 20      @ see length if necessary 
term_fin:

/* structure sigaction see doc linux */
    .struct  0
sa_handler:
    .struct  sa_handler + 4 
sa_mask:
    .struct  sa_mask + 4 
sa_flags:
    .struct  sa_flags + 4 
sa_sigaction:
    .struct  sa_sigaction + 4 
sa_fin:

/* structure poll see doc linux */
    .struct  0
poll_fd:                            @   File Descriptor
    .struct  poll_fd + 4 
poll_events:                        @  events mask
    .struct  poll_events + 4 
poll_revents:                       @ events returned
    .struct  poll_revents + 4 
poll_fin:

/*********************************/
/* Initialized data              */
/*********************************/
.data
szMessPgmOk:        .asciz "End program OK.\n"
szMessErreur:       .asciz "Error detected.\n"
sMessResult:        .ascii "Value  : "
sMessValeur:        .fill 11, 1, ' '            @ size => 11
szCarriageReturn:   .asciz "\n"


.align 4

/*********************************/
/* UnInitialized data            */
/*********************************/
.bss  
.align 4
iEnd:           .skip 4                          @ 0 loop  1 = end loop
iTouche:        .skip BUFSIZE                    @ value key pressed
stOldtio:       .skip term_fin                   @ old terminal state
stCurtio:       .skip term_fin                   @ current terminal state
stSigAction:    .skip sa_fin                     @ area signal structure
stSigAction1:   .skip sa_fin
stPoll1:        .skip poll_fin                   @ area poll structure
stPoll2:        .skip poll_fin

szBuffer:       .skip BUFSIZE
/*********************************/
/*  code section                 */
/*********************************/
.text
.global main 
main:                                            @ entry of program 
    bl initTerm                                  @ terminal init
    mov r2,#0
    ldr r3,iAdrszBuffer
1:
    bl getKey                                    @ read one key
    cmp r0,#113                                  @ saisie q ?
    beq 3f
    cmp r0,#81                                   @ saisie Q ?
    beq 3f
    cmp r0,#0xA                                  @ <enter> ?
    beq 2f
    strb r0,[r3,r2]                              @ store byte in buffer
    add r2,#1
    b 1b
2:                                               @ display buffer
    mov r0,#0                                    @ store 0 final
    strb r0,[r3,r2]
    mov r0,r3
    bl affichageMess
    ldr r0,iAdrszCarriageReturn
    bl affichageMess
    mov r2,#0
    b 1b
3:
    bl restauTerm                                 @ terminal restaur
    ldr r0,iAdrszMessPgmOk                        @ display end message
    bl affichageMess
100:                                              @ standard end of the program 
    mov r0, #0                                    @ return code
    mov r7, #EXIT                                 @ request to exit program
    svc #0                                        @ perform the system call
iAdrszBuffer:         .int szBuffer
/*********************************/
/* init terminal state            */
/*********************************/
initTerm:
    push {r0,r1,r2,r7,lr}
    /* read terminal state */
    mov r0,#STDIN                                @ input console
    mov r1,#TCGETS
    ldr r2,iAdrstOldtio
    mov r7, #IOCTL                               @ call system Linux
    svc #0 
    cmp r0,#0                                    @ error ?
    beq 1f
    ldr r1,iAdrszMessErreur                      @ error message
    bl   displayError
    b 100f
1:
    adr r0,sighandler                            @ adresse routine traitement signal
    ldr r1,iAdrstSigAction                       @ adresse structure sigaction
    str r0,[r1,#sa_handler]                      @ maj handler
    mov r0,#SIGINT                               @ signal type
    ldr r1,iAdrstSigAction
    mov r2,#0                                    @ NULL
    mov r7, #SIGACTION                           @ call system
    svc #0 
    cmp r0,#0                                    @ error ?
    bne 98f
    mov r0,#SIGQUIT
    ldr r1,iAdrstSigAction
    mov r2,#0                                    @ NULL
    mov r7, #SIGACTION                           @ call system 
    svc #0 
    cmp r0,#0                                    @ error ?
    bne 98f
    mov r0,#SIGTERM
    ldr r1,iAdrstSigAction
    mov r2,#0                                    @ NULL
    mov r7, #SIGACTION                           @ appel systeme 
    svc #0 
    cmp r0,#0
    bne 98f
    @
    adr r0,iAdrSIG_IGN                           @ address signal igonre function
    ldr r1,iAdrstSigAction1
    str r0,[r1,#sa_handler]
    mov r0,#SIGTTOU                              @invalidate other process signal
    ldr r1,iAdrstSigAction1
    mov r2,#0                                    @ NULL
    mov r7,#SIGACTION                            @ call system 
    svc #0 
    cmp r0,#0
    bne 98f
    @
    /* read terminal current state  */
    mov r0,#STDIN
    mov r1,#TCGETS
    ldr r2,iAdrstCurtio                          @ address current termio
    mov r7,#IOCTL                                @ call systeme 
    svc #0 
    cmp r0,#0                                    @ error ?
    bne 98f
    mov r2,#ICANON | ECHO                        @ no key pressed echo on display
    mvn r2,r2                                    @ and one key 
    ldr r1,iAdrstCurtio
    ldr r3,[r1,#term_c_lflag]
    and r3,r2                                    @ add flags 
    str r3,[r1,#term_c_lflag]                    @ and store
    mov r0,#STDIN                                @ maj terminal current state 
    mov r1,#TCSETS
    ldr r2,iAdrstCurtio
    mov r7, #IOCTL                               @ call system
    svc #0 
    cmp r0,#0
    beq 100f
98:                                               @ error display
    ldr r1,iAdrszMessErreur                       @ error message
    bl   displayError
100:
    pop {r0,r1,r2,r7,lr}
    bx lr

/*********************************/
/* read key                      */
/*********************************/
getKey:
    push {r1,r2,r7,lr}
    ldr r2,iAdriTouche                           @ key address
    mov r0,#0                                    @ raz key
    str r0,[r2]
1:
    ldr r0,iAdriEnd                              @ if signal ctrl-c  -> end
    ldr r0,[r0]
    cmp r0,#0
    bne 100f
    ldr r0,iAdrstPoll1                            @ address structure poll
    mov r1,#STDIN
    str r1,[r0,#poll_fd]                          @ maj FD
    mov r1,#POLLIN                                @ action code
    str r1,[r0,#poll_events]
    mov r1,#1                                     @ items number structure poll
    mov r2,#0                                     @ timeout = 0 
    mov r7,#SYSPOLL                               @ call system POLL
    svc #0 
    cmp r0,#0                                     @ key pressed ?
    ble 1b                                        @ no key pressed -> loop
                                                  @ read key
    mov r0,#STDIN                                 @ File Descriptor
    ldr r1,iAdriTouche                            @ buffer address
    mov r2,#BUFSIZE                               @ buffer size
    mov r7,#READ                                  @ read key
    svc #0
    cmp r0,#0                                     @ error ?
    ble 98f
    ldr r2,iAdriTouche                            @ key address
    ldr r0,[r2]
    b 100f
98:                                               @ error display
    ldr r1,iAdrszMessErreur                       @ error message
    bl   displayError
100:
    pop {r1,r2,r7,lr}
    bx lr

/*********************************/
/* restaur terminal state        */
/*********************************/
restauTerm:
    push {r0,r1,r7,lr}
    mov r0,#STDIN                                 @ end then restaur begin state terminal
    mov r1,#TCSETS
    ldr r2,iAdrstOldtio
    mov r7,#IOCTL                                 @ call system  
    svc #0
    cmp r0,#0
    beq 100f
    ldr r1,iAdrszMessErreur                       @ error message
    bl   displayError
100:
    pop {r1,r2,r7,lr}
    bx lr

iAdrsMessValeur:          .int sMessValeur
iAdrszMessErreur:         .int szMessErreur
iAdrszCarriageReturn:     .int szCarriageReturn
iAdrstOldtio:             .int stOldtio
iAdrstCurtio:             .int stCurtio
iAdrstSigAction:          .int stSigAction
iAdrstSigAction1:         .int stSigAction1
iAdrszMessPgmOk:          .int szMessPgmOk
iAdrsMessResult:          .int sMessResult
iAdrSIG_IGN:              .int 1
iAdriEnd:                 .int iEnd
iAdrstPoll1:              .int stPoll1
iAdriTouche:              .int iTouche

/******************************************************************/
/*     signal processing                                     */ 
/******************************************************************/
sighandler:
    push {r0,r1}
    ldr r0,iAdriEnd
    mov r1,#1                 @ maj zone end
    str r1,[r0]
    pop {r0,r1}
    bx lr
/***************************************************/
/*      ROUTINES INCLUDE                           */
/***************************************************/
.include "../affichage.inc"

AWK[edit]

# syntax: TAWK -f KEYBOARD_INPUT_FLUSH_THE_KEYBOARD_BUFFER.AWK
BEGIN {
    while (kbhit()) {
      getkey()
    }
    exit(0)
}

Axe[edit]

While getKey(0)
End

Bash[edit]

The -t 0 should theoretically work, but it does not seem to for tests that have been tried in cygwin and FreeBSD.

while read -t 0.01; do
    true
done

BASIC[edit]

Applesoft BASIC[edit]

10  IF  PEEK (49152) > 127 THEN C =  PEEK (49168): GOTO 10

BASIC256[edit]

while key <> "" : end while
print "Keyboard buffer flushed"

Commodore BASIC[edit]

GET will fetch a single byte from the keyboard buffer, if one is present. The keyboard buffer will hold up to ten bytes before ignoring additional input.

10 print chr$(147);chr$(14)
25 get k$:if k$<>"" then 25:rem empty buffer
40 print chr$(19):print " Program halted for 10000 counts. "
45 print:print " Type characters to fill the buffer."
50 for i=1 to 10000:next
60 print:print " Characters in the buffer are:":print:print " ";
65 get k$:print k$;
70 for t=1 to 100:next
75 if k$<>"" then 65
80 print
85 end
Output:
 Program halted for 10000 counts. 

 Type characters to fill the buffer.

 Characters in the buffer are: 

 abCdefGH12

ready.

Locomotive Basic[edit]

10 CLEAR INPUT

(Only available in BASIC 1.1 though, i.e. not on the CPC 464.)

QBasic[edit]

Works with: QBasic version 1.1
Works with: QuickBasic version 4.5
Works with: True BASIC
DO WHILE INKEY$ <> ""
LOOP
PRINT "Keyboard buffer flushed"
END

Run BASIC[edit]

Works with: QBasic
Works with: FreeBASIC
while inkey$ <> "" : wend
print "Keyboard buffer flushed"

True BASIC[edit]

Works with: QBasic
DO WHILE INKEY$ <> ""
LOOP
PRINT "Keyboard buffer flushed"
END

ZX Spectrum Basic[edit]

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.

10 IF INKEY$ <> "" THEN GO TO 10

BBC BASIC[edit]

      *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

or:

      REPEAT UNTIL INKEY$(0)=""

C[edit]

Simple solution for stdin[edit]

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

int main(int argc, char* argv[])
{
    // Get a chance to make stdin input buffer dirty.
    //
    char text[256];
    getchar();

    // This DOES NOT WORK properly on all modern systems including Linux & W10.
    // Obsolete, don't use this. BTW, there is no fpurge in MSVC libs in 2020.
    //
    // fflush(stdin);

    // Always works. Readed characters may remain somethere in RAM.
    //
    fseek(stdin, 0, SEEK_END);

    // A very dirty solution - an unbuffered stream does not need any flushing.
    //
    // setvbuf(stdin, NULL, _IONBF, 0);

    // Now we are able to check if the buffer is really empty.
    //
    fgets(text, sizeof(text), stdin);
    puts(text);

    return EXIT_SUCCESS;
}

POSIX[edit]

Library: 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;
}

Solution for MSVC conio[edit]

Library: Windows MSVC
#include <conio.h>
#include <tchar.h>

// Uses only CRT functions. No need to include 'Windows.h'.

void Kbflush(void)
{
    while (_kbhit())
    {
        // The _gettch function reads a single character without echoing it. When reading
        // a function key or an arrow key, it must be called twice; the first call returns
        // 0x00 or 0xE0 and the second call returns the actual key code. Source: MSDN.
        int ch = _gettch();
        if (ch == 0x00 || ch == 0xE0)
            (void)_gettch();
    }
}

int _tmain(void)
{
    Kbflush();
    return 0;
}

D[edit]

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[edit]

$ wait 0::10  ! gives us 10 seconds to get keystrokes into the type-ahead buffer
$ on control_y then $ goto clean
$ set terminal /noecho
$ loop: read /prompt="" /time=0 sys$command /error=clean buffer
$ goto loop
$ clean:
$ set terminal /echo
Output:
$ @flush_the_keyboard_buffer  ! ignores/discards keystrokes for 10 seconds
$

Delphi[edit]

program Flush_the_keyboard_buffer;

{$APPTYPE CONSOLE}

uses
  Winapi.Windows;

var
  StdIn: THandle;

begin
  StdIn := GetStdHandle(STD_INPUT_HANDLE);
  Writeln('Press any key you want, they will be erased:');
  Sleep(5000);
  FlushConsoleInputBuffer(StdIn);
  Writeln('Now press any key you want, they will NOT be erased:');
  readln;
end.

ERRE[edit]

!$KEY
..........
REPEAT
   GET(K$)
UNTIL K$=""
..........

Note: Test after K$ can be replaced with LEN(K$)=0.

Euphoria[edit]

while get_key()!=-1 do
end while

FreeBASIC[edit]

' FB 1.05.0 Win64

' Get characters from the keyboard buffer until there are none left
While Inkey <> "" : Wend 
Print "Keyboard buffer flushed"
Sleep

Go[edit]

Library: 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()
}
package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {
	stdin := bufio.NewReader(os.Stdin)

	fmt.Println("Please enter an integer: ")

	var i1 int

	for {
		_, err := fmt.Fscan(stdin, &i1)
		if err == nil {
			break
		}
		stdin.ReadString('\n')
		fmt.Println("Sorry, invalid input. Please enter an integer: ")
		flush(stdin)
	}

	fmt.Println(i1)
}

func flush(reader *bufio.Reader) {
	var i2 int
	for i2 = 0; i2 < reader.Buffered(); i2++ {
		reader.ReadByte()
	}
}

Haskell[edit]

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[edit]

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.

Icon and Unicon[edit]

The following solution works in both Icon and Unicon.

procedure flushKB()
    while kbhit() do getch()   # flush input
end

Julia[edit]

Library: 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[edit]

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[edit]

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

MiniScript[edit]

Works with: Mini Micro
key.clear

Nim[edit]

Library: POSIX
const TCIFLUSH: cint = 0
proc tcflush(fd, queue_selector: cint): cint {.header: "termios.h".}

discard tcflush(cint(getFileHandle(stdin)), TCIFLUSH)

Oforth[edit]

import: console

System.Console flush

Perl[edit]

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';

Phix[edit]

while get_key()!=-1 do end while

PicoLisp[edit]

(while (key 10))

PowerShell[edit]

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[edit]

While Inkey(): Wend

Python[edit]

def flush_input():
    try:
        import msvcrt
        while msvcrt.kbhit():
            msvcrt.getch()
    except ImportError:
        import sys, termios
        termios.tcflush(sys.stdin, termios.TCIOFLUSH)

Racket[edit]

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)))

Raku[edit]

(formerly Perl 6)

Works with: Rakudo version 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 "|";
}

REXX[edit]

This will work for Regina:

call dropbuf

This will work for CMS REXX, PC/REXX, Personal REXX, and TSO REXX:

'DROPBUF'

Ring[edit]

# Project: Keyboard input/Flush the keyboard buffer

Fflush(stdin)

Ruby[edit]

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 version 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[edit]

def flush() { out.flush() }

Seed7[edit]

The Seed7 library keybd.s7i defines the file KEYBOARD, which provides functions like keypressed and getc.

while keypressed(KEYBOARD) do
  ignore(getc(KEYBOARD));
end while;

Sidef[edit]

Translation of: 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[edit]

# 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[edit]

Key_Purge()

Wren[edit]

There is currently no direct way to flush the keyboard buffer from Wren-cli.

However, the System.readByte() method reads and removes the next byte from the buffer, blocking the fiber until enter is pressed. Consequently, the following code will only flush the buffer if enter is the last key pressed.

It is necessary to type in some keys first (and have them echoed) to demonstrate that it is in fact working. 'Raw' mode can't be used here as keyboard input is not buffered in that mode.

import "io" for Stdin

System.print("Press some keys followed by enter.")
while (true) {
   var b = Stdin.readByte() // reads and removes a key from the buffer
   System.print("Removed key with code %(b).")
   if (b == 10) break      // buffer will be empty when enter key pressed
}
System.print("Keyboard buffer is now empty.")
Output:

Sample session when the keys a, b, c, d followed by enter are pressed:

Press some keys followed by enter.
abcd
Removed key with code 97.
Removed key with code 98.
Removed key with code 99.
Removed key with code 100.
Removed key with code 10.
Keyboard buffer is now empty.

XPL0[edit]

code OpenI=13;
OpenI(0)