Q42796: Background Colors Limited to 0 Through 7 in Text Mode

Article: Q42796
Product(s): See article
Version(s): 5.10
Operating System(s): MS-DOS
Keyword(s): ENDUSER | s_quickc | mspl13_c
Last Modified: 15-JAN-1990

The function _setbkcolor() displays only colors "0" through "7" when
in text mode. This is a limit of the hardware, not the library
function.

Two bytes are allocated for each character displayed on a text 80 x 25
screen. The first byte is the ASCII code of the character; the second
is the attribute byte.

The attribute byte contains the information about the foreground and
background attributes of the character. Four bits of this byte are
allocated for the foreground color. The most significant bit of the
foreground color is set aside for intensity or highlight. However, of
the 4 bits allocated for the background color, the most significant
bit is reserved to indicate a blinking or a nonblinking state.

The layout of the attribute bytes is as follows:

            7    6   5   4   3   2   1   0
         +----+------------+---+------------+
         | BL | background | I | foreground |
         +----+------------+---+------------+

Since only 3 bits are used to indicate the background color, only
numbers from 0 through 7 can be represented. For this reason, only
colors 0 through 7 are available as background colors for
_setbkcolor().

On most display adapters, you can set the adapter such that the blink
bit becomes a background intensity bit. See your hardware technical
reference or the "Programmer's Guide to PC and PS/2 Video Systems"
(Richard Wilton, Microsoft Press) for more information.

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.