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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[edit]

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.

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
}

BASIC[edit]

Applesoft BASIC[edit]

 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))

Locomotive Basic[edit]

10 LOCATE 3,6
20 a$=COPYCHR$(#0)

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[edit]

The top left corner is (1, 1).

c$ = CHR$(SCREEN(6, 3))

ZX Spectrum Basic[edit]

 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)

BBC BASIC[edit]

      PRINT TAB(2,5) "Here"
char$ = GET$(2,5)
PRINT ''"Character at column 3 row 6 was " char$

C[edit]

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
#include <windows.h>
#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;
}

Racket[edit]

Works in a CMD box on Windows:

 
#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))
 

REXX[edit]

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
/*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.*/

XPL0[edit]

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
]