Terminal control/Positional read

Terminal control/Positional read is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Determine the character displayed on the screen at column 3, row 6 and store that character in a variable.

BASIC

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.

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>

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>

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

<lang rexx>/*REXX program demonstrates reading a char at specific screen location.*/

row=20 /*point to row twenty. */ col=55 /*point co column fifty-five. */ howMany=3 /*read a trio of characters. */

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

other=scrRead(40,55,2) /*same thing, but for row forty. */</lang>