Q66774: _wrapon() Function Will Prevent Text Windows From Scrolling

Article: Q66774
Product(s): See article
Version(s): 5.10 6.00 6.00a | 6.00 6.00a
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | S_QUICKC | mspl13_c
Last Modified: 9-NOV-1990

A text window filled with characters will normally scroll when a
character is placed into the last position in the lower-right corner
of the window. You can use the _wrapon() function to prevent the
window text from scrolling while still allowing a character to be
placed in the last position.

Functions, such as _outtext(), are designed such that the current
cursor location is one character PAST the last output position. Thus,
when the cursor is turned on, it blinks just past the most recently
written character.

Note, This assumes that you are using text mode. In graphics mode [or
with _outgtext()], this is not a problem.

In the case where text wrap is enabled and a character is written to
the last position of a line, the cursor must blink on the first
position of the next line. On the last line of a window, this will
will cause a scroll. The workaround for situations such as this is to
turn off text wrap while drawing the last character, which is why
_wrapon() is provided.

The _wrapon() function accepts either of two parameters: _GWRAPON or
_GWRAPOFF. _GWRAPOFF is the parameter that is needed in this case. The
sample code below demonstrates this problem and the use of _wrapon()
to correct it.

Sample Code
-----------

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <graph.h>
#include <conio.h>
#include <string.h>

void main(void)
{
   int i, response;
   char ch[11];

   _clearscreen( _GCLEARSCREEN );
   printf("\n\nDo you want text wrap on? (y/n)");
   response = getch();
   if ( _toupper(response) == 'Y' )
      _wrapon( _GWRAPON );
   else
      _wrapon( _GWRAPOFF );

   // Label screen grid for easy reference

   _clearscreen( _GCLEARSCREEN );
   _outtext( "123456789" );
   for( i = 2; i <= 9; i++ )
   {
      _settextposition( i, 1 );
      _outtext( itoa( i, ch, 10 ) );
   }

   // Set a text window and fill all but last line

   _settextwindow( 3, 3, 9, 9 );
   for( i = 1; i <= 6; i++ )
   {
      _settextposition( i, 1 );
      memset( ch, i+'0', 10 );
      _outmem( ch, 7 );
   }

   // Fill last line, all but last character

   _settextposition( i, 1 );
   memset( ch, i + '0', 10 );
   _outmem( ch, 6 );
   getch();

   // Fill last character in window -- the entire window will scroll
   //   if text wrap was specified

   _outmem( ch, 1 );
   getch();
   _clearscreen( _GCLEARSCREEN );
}

Note: This program utilizes the _outmem() function, which did not
exist in the C version 5.10 or QuickC 2.00 libraries. To build this
program with either of these compilers, the program must be rewritten
without the _outmem() function.

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