Terminal control/Positional read

From Rosetta Code
Task
Terminal control/Positional read
You are encouraged to solve this task according to the task description, using any language you may know.

Determine the character displayed on the screen at column 3, row 6 and store that character in a variable. Note that it is permissible to utilize system or language provided methods or system provided facilities, system maintained records or available buffers or system maintained display records to achieve this task, rather than query the terminal directly, if those methods are more usual for the system type or language.

AutoHotkey

Works with: AutoHotkey_L

AutoHotkey is not built for the command line, so we need call the WinAPI directly.

For fun, this writes random characters to the command window so that it has something to retrieve.

<lang AHK>DllCall( "AllocConsole" ) ; create a console if not launched from one hConsole := DllCall( "GetStdHandle", int, STDOUT := -11 ) Loop 10 { Loop 10 { Random, asc, % asc("A"), % Asc("Z") WriteConsole(hConsole, Chr(asc)) } WriteConsole(hConsole, "`n") }

MsgBox % ReadConsoleOutputCharacter(hConsole, 1, 3, 6)

=== The below simply wraps part of the WinAPI ===

WriteConsole(hConsole, text){ VarSetCapacity(out, 16) If DllCall( "WriteConsole", UPtr, hConsole, Str, text, UInt, StrLen(text) , UPtrP, out, uint, 0 ) return out return 0 } ReadConsoleOutputCharacter(hConsole, length, x, y){ VarSetCapacity(out, length * (1 << !!A_IsUnicode)) VarSetCapacity(n, 16) if DllCall( "ReadConsoleOutputCharacter" , UPtr, hConsole , Str, out , UInt, length , UInt, x | (y << 16) , UPtrP, n )

&& VarSetCapacity(out, -1) return out return 0 }</lang>

BASIC

Applesoft BASIC

<lang ApplesoftBasic> 10 DEF FN C(H) = SCRN( H - 1,(V - 1) * 2) + SCRN( H - 1,(V - 1) * 2 + 1) * 16

20  LET V = 6:C$ =  CHR$ ( FN C(3))</lang>

Locomotive Basic

<lang locobasic>10 LOCATE 3,6 20 a$=COPYCHR$(#0)</lang>

Amstrad CPC screen memory only stores pixels but no character information (as opposed to e.g. the C64), so the firmware routine (TXT_UNWRITE) called by BASIC works by trying to find a match between screen pixels and the shape of a currently defined character. If the character table or screen pixels in the area of the character are changed between writing and reading, COPYCHR$ will therefore fail.

QBasic

The top left corner is (1, 1).

<lang qbasic>c$ = CHR$(SCREEN(6, 3))</lang>

ZX Spectrum Basic

<lang basic> 10 REM The top left corner is at position 0,0

20 REM So we subtract one from the coordinates
30 LET c$ = SCREEN$(5,2)</lang>

BBC BASIC

<lang bbcbasic> PRINT TAB(2,5) "Here"

     char$ = GET$(2,5)
     PRINT "Character at column 3 row 6 was " char$</lang>
Works with: all BBC BASICs
that support calling OSBYTE

<lang bbcbasic> PRINT TAB(2,5) "Here"

     PRINT TAB(2,5);                         : REM Position cursor over character to read
     A%=&87:char%=((USR&FFF4)AND&FF00)DIV256 : REM Ask operating system to read character
     PRINT "Character at column 3 row 6 was CHR$(";char%;")"</lang>

C

With the Windows console, call GetConsoleScreenBufferInfo() to find the top-left corner of the display screen. Then add (3, 6) to the top-left corner and call ReadConsoleOutputCharacterW() to read character. This program reckons that the top-left corner is (0, 0).

Library: Win32

<lang c>#include <windows.h>

  1. include <wchar.h>

int main() { CONSOLE_SCREEN_BUFFER_INFO info; COORD pos; HANDLE conout; long len; wchar_t c;

/* Create a handle to the console screen. */ conout = CreateFileW(L"CONOUT$", GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, 0, NULL); if (conout == INVALID_HANDLE_VALUE) return 1;

/* Where is the display window? */ if (GetConsoleScreenBufferInfo(conout, &info) == 0) return 1;

/* c = character at position. */ pos.X = info.srWindow.Left + 3; /* Column */ pos.Y = info.srWindow.Top + 6; /* Row */ if (ReadConsoleOutputCharacterW(conout, &c, 1, pos, &len) == 0 || len <= 0) return 1;

wprintf(L"Character at (3, 6) had been '%lc'\n", c); return 0; }</lang>

Common Lisp

ncurses

To interface the ncurses C library from Lisp, the croatoan library is used. <lang lisp>(defun positional-read ()

 (with-screen (scr :input-blocking t :input-echoing nil :cursor-visible nil)
   ;; print random characters in a 10x20 grid
   (loop for i from 0 to 9 do
        (loop for j from 0 to 19 do
             (add-char scr (+ 33 (random 94)) :y i :x j)))
   ;; highlight char to extract at row 6 column 3
   (change-attributes scr 1 (list :reverse) :y 5 :x 2)
   (refresh scr)
   ;; wait for keypress
   (get-char scr)
   ;; extract char from row 6 column 3
   (let ((char (extract-char scr :y 5 :x 2)))
     ;; then print it out again
     (move scr 11 0)
     (format scr "extracted char: ~A" char))
   (refresh scr)
   (get-char scr)))</lang>

Go

Translation of: Kotlin

<lang go>package main

/*

  1. include <windows.h>
  • /

import "C" import "fmt"

func main() {

   for i := 0; i < 80*25; i++ {
       fmt.Print("A")  // fill 80 x 25 console with 'A's
   }
   fmt.Println()
   conOut := C.GetStdHandle(C.STD_OUTPUT_HANDLE)
   info := C.CONSOLE_SCREEN_BUFFER_INFO{}
   pos := C.COORD{}
   C.GetConsoleScreenBufferInfo(conOut, &info)
   pos.X = info.srWindow.Left + 3 // column number 3 of display window
   pos.Y = info.srWindow.Top + 6  // row number 6 of display window
   var c C.wchar_t
   var le C.ulong
   ret := C.ReadConsoleOutputCharacterW(conOut, &c, 1, pos, &le)
   if ret == 0 || le <= 0 {
       fmt.Println("Something went wrong!")
       return
   }
   fmt.Printf("The character at column 3, row 6 is '%c'\n", c) 

}</lang>

Output:
The character at column 3, row 6 is 'A'

Julia

Translation of: Raku

<lang julia>using LibNCurses

randtxt(n) = foldl(*, rand(split("1234567890abcdefghijklmnopqrstuvwxyz", ""), n))

initscr()

for i in 1:20

   LibNCurses.mvwaddstr(i, 1, randtxt(50))

end

row = rand(1:20) col = rand(1:50) ch = LibNCurses.winch(row, col) LibNCurses.mvwaddstr(col, 52, "The character at ($row, $col) is $ch.") ) </lang>

Kotlin

This is based on the C entry and works on Windows 10: <lang scala>// Kotlin Native version 0.3

import kotlinx.cinterop.* import win32.*

fun main(args: Array<String>) {

   for (i in 0 until (80 * 25)) print("A")  // fill 80 x 25 console with 'A's
   println()
   memScoped {
       val conOut = GetStdHandle(-11)
       val info = alloc<CONSOLE_SCREEN_BUFFER_INFO>()       
       val pos = alloc<COORD>()
       GetConsoleScreenBufferInfo(conOut, info.ptr)
       pos.X = (info.srWindow.Left + 3).toShort()  // column number 3 of display window
       pos.Y = (info.srWindow.Top + 6).toShort()   // row number 6 of display window
       val c = alloc<wchar_tVar>()
       val len = alloc<IntVar>()
       ReadConsoleOutputCharacterW(conOut, c.ptr, 1, pos.readValue(), len.ptr)
       if (len.value == 1) {
           val ch = c.value.toChar()
           println("The character at column 3, row 6 is '$ch'")
       }
       else println("Something went wrong!")
   }   

}</lang>

Output:
The character at column 3, row 6 is 'A'

Phix

<lang Phix>-- -- demo\rosetta\Positional_read.exw -- ================================ -- position(6,1) -- line 6 column 1 (1-based) puts(1,"abcdef") integer {ch,attr} = get_screen_char(6,3) printf(1,"\n\n=>%c",ch) {} = wait_key()</lang>

Output:





abcdef

=>c

PowerShell

This gets the character at position (3, 6) of the buffer, not necessarily of the screen. <lang powershell> $coord = [System.Management.Automation.Host.Coordinates]::new(3, 6) $rect = [System.Management.Automation.Host.Rectangle]::new($coord, $coord) $char = $Host.UI.RawUI.GetBufferContents($rect).Character </lang>

Python

<lang python>import curses from random import randint


  1. Print random text in a 10x10 grid

stdscr = curses.initscr() for rows in range(10):

   line = .join([chr(randint(41, 90)) for i in range(10)])
   stdscr.addstr(line + '\n')
  1. Read

icol = 3 - 1 irow = 6 - 1 ch = stdscr.instr(irow, icol, 1).decode(encoding="utf-8")

  1. Show result

stdscr.move(irow, icol + 10) stdscr.addstr('Character at column 3, row 6 = ' + ch + '\n') stdscr.getch()

curses.endwin() </lang>

Output:
T@4;4G,XIJ
>C+PE0)RM;
JEV6B/8E?H
FSC>41UIGR
V>41JMXMOW
IY0*KH6M;B  Character at column 3, row 6 = 0
-6<UL*>DU7
MZ))<5D:B8
.@UB/P6UQ)
<9HYH)<ZJF

Racket

Works in a CMD box on Windows: <lang racket>

  1. lang racket

(require ffi/unsafe ffi/unsafe/define) (define-ffi-definer defwin #f) (defwin GetStdHandle (_fun _int -> _pointer)) (defwin ReadConsoleOutputCharacterA

 (_fun _pointer _pointer _uint _uint [len : (_ptr o _uint)] -> _bool))

(define b (make-bytes 1 32)) (and (ReadConsoleOutputCharacterA (GetStdHandle -11) b 1 #x50002)

    (printf "The character at 3x6 is <~a>\n" b))

</lang>

Raku

(formerly Perl 6)

Translation of: Python

<lang perl6>use NCurses;

  1. Reference:
  2. https://github.com/azawawi/perl6-ncurses
  1. Initialize curses window

my $win = initscr() or die "Failed to initialize ncurses\n";

  1. Print random text in a 10x10 grid

for ^10 { mvaddstr($_ , 0, (for ^10 {(41 .. 90).roll.chr}).join )};

  1. Read

my $icol = 3 - 1; my $irow = 6 - 1;

my $ch = mvinch($irow,$icol);

  1. Show result

mvaddstr($irow, $icol+10, 'Character at column 3, row 6 = ' ~ $ch.chr);

mvaddstr( LINES() - 2, 2, "Press any key to exit..." );

  1. Refresh (this is needed)

nc_refresh;

  1. Wait for a keypress

getch;

  1. Cleanup

LEAVE {

   delwin($win) if $win;
   endwin;

}</lang>

Output:
+W18:5I<1N
N-I.HG45SK
BFJY8:AK)8
J+4U<H1++:
RP>BX-/19Y
URDESVX;HX  Character at column 3, row 6 = D
J7+X3@E<BG
M;?2U<8+FI
)@BG,:D)O1
)>A-=LDY-.












  Press any key to exit...

REXX

The REXX doesn't have any cursor or screen management tools, but some REXX interpreters have added the functionality via different methods.

Works with: PC/REXX
Works with: Personal REXX

<lang rexx>/*REXX program demonstrates reading a char at specific screen location.*/ row = 6 /*point to row six. */ col = 3 /*point to column three. */ howMany = 1 /*read one character. */

stuff = scrRead(row, col, howMany) /*this'll do it. */

other = scrRead(40, 6, 1) /*same thing, but for row forty. */

                                      /*stick a fork in it, we're done.*/</lang>

TXR

<lang txrlisp>;;; Type definitions and constants

(typedef BOOL (enum BOOL FALSE TRUE)) (typedef HANDLE cptr) (typedef WCHAR wchar) (typedef DWORD uint32) (typedef WORD uint16) (typedef SHORT short)

(typedef COORD

        (struct COORD
          (X SHORT)
          (Y SHORT)))

(typedef SMALL_RECT

        (struct SMALL_RECT
          (Left SHORT)
          (Top SHORT)
          (Right SHORT)
          (Bottom SHORT)))

(typedef CONSOLE_SCREEN_BUFFER_INFO

        (struct CONSOLE_SCREEN_BUFFER_INFO
          (dwSize COORD)
          (dwCursorPosition COORD)
          (wAttributes WORD)
          (srWindow SMALL_RECT)
          (dwMaximumWindowSize COORD)))
Various constants

(defvarl STD_INPUT_HANDLE (- #x100000000 10)) (defvarl STD_OUTPUT_HANDLE (- #x100000000 11)) (defvarl STD_ERROR_HANDLE (- #x100000000 12))

(defvarl NULL cptr-null) (defvarl INVALID_HANDLE_VALUE (cptr-int -1))

Foreign Function Bindings

(with-dyn-lib "kernel32.dll"

 (deffi GetStdHandle "GetStdHandle" HANDLE (DWORD))
 (deffi GetConsoleScreenBufferInfo "GetConsoleScreenBufferInfo"
        BOOL (HANDLE (ptr-out CONSOLE_SCREEN_BUFFER_INFO)))
 (deffi ReadConsoleOutputCharacter "ReadConsoleOutputCharacterW"
        BOOL (HANDLE (ptr-out (array 1 WCHAR))
                      DWORD COORD (ptr-out (array 1 DWORD)))))
Now the character at <2, 5> -- column 3, row 6.

(let ((console-handle (GetStdHandle STD_OUTPUT_HANDLE)))

 (when (equal console-handle INVALID_HANDLE_VALUE)
   (error "couldn't get console handle"))
 (let* ((cinfo (new CONSOLE_SCREEN_BUFFER_INFO))
        (getinfo-ok (GetConsoleScreenBufferInfo console-handle cinfo))
        (coord (if getinfo-ok
                 ^#S(COORD X ,(+ 2 cinfo.srWindow.Left)
                           Y ,(+ 5 cinfo.srWindow.Top))
                 #S(COORD X 0 Y 0)))
        (chars (vector 1))
        (nread (vector 1))
        (read-ok (ReadConsoleOutputCharacter console-handle chars
                                             1 coord nread)))
   (when (eq getinfo-ok 'FALSE)
     (error "GetConsoleScreenBufferInfo failed"))
   (prinl cinfo)
   (when (eq read-ok 'FALSE)
     (error "ReadConsoleOutputCharacter failed"))
   (unless (plusp [nread 0])
     (error "ReadConsoleOutputCharacter read zero characters"))
   (format t "character is ~s\n" [chars 0])))</lang>

Notes:

  • An ptr-out to an array of 1 DWORD is used for the number of characters out parameter. The FFI type (ptr-out DWORD) cannot work as a function argument, because integer objects are not mutable, and there isn't any concept of taking the address of a variable. A vector of 1 integer is mutable, and by making such a vector correspond with the FFI type (array 1 DWORD), the necessary semantics is achieved.
  • The quasiquote expression ^#S(COORD X ,(+ 2 cinfo.srWindow.Left) Y ,(+ 5 cinfo.srWindow.Top)) is equivalent to (new COORD X (+ 2 cinfo.srWindow.Left) Y (+ 5 cinfo.srWindow.Top)). It is done this way to demonstrate support for structure quasiquoting.

XPL0

<lang XPL0>include c:\cxpl\stdlib; int C; [Cursor(3, 6); \move cursor to column 3, row 6 (top left = 0,0) \Call BIOS interrupt routine to read character (& attribute) at cursor position C:= CallInt($10, $0800, 0) & $00FF; \mask off attribute, leaving the character ]</lang>