Q43527: BASIC Program to Read Characters from the Screen into a String

Article: Q43527
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom | mspl13_basic
Last Modified: 14-DEC-1989

The program below demonstrates a method to read text that is printed
on the screen into a BASIC string variable. The program accesses video
memory (at segment B000 hex) to read the characters from the screen.

This information applies to Microsoft QuickBASIC Versions 4.00, 4.00b,
and 4.50, to Microsoft BASIC Compiler Versions 6.00 and 6.00b, and to
Microsoft BASIC PDS Version 7.00.

For a color display, you must change the address of the DEF SEG
statement in the function from HEX B000 to HEX B800. Note that any
attributes (blinking, highlight, etc.) will be lost when the text is
put into the string.

The program is as follows:

DECLARE FUNCTION readstr$ (xline%, xstart%, xstop%)

CLS
PRINT "Now is the time"         'Put some text on the screen
PRINT "for all good men"
PRINT "to come to the aid"
PRINT "of their country."

a$ = readstr$(1, 1, 6)          'Read the first six characters of the
                                'first line  (i.e. "Now is")

b$ = readstr$(4, 10, 18)        'Read the last nine characters (10-18)
                                'on line four (i.e. "country.")
LOCATE 10, 1
PRINT "A$ = "; a$
PRINT "B$ = "; b$

'readstr$ takes three integers and returns a string.
'The integers are:    1) The line on the screen to read from
'                     2) The starting character position
'                     3) The ending character position
'It returns a string containing the characters on the screen
'on the specified line between the start and stop positions.
'
FUNCTION readstr$ (xline%, xstart%, xstop%)

  DEF SEG = &HB000              'Change to B800 for color display

  fstart% = (160 * (xline% - 1)) + (2 * (xstart% - 1))
  fstop% = (160 * (xline% - 1)) + (2 * (xstop% - 1))
  FOR x% = fstart% TO fstop% STEP 2
    s$ = s$ + CHR$(PEEK(x%))
  NEXT x%
  readstr$ = s$
END FUNCTION

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