Q43914: C: Text Modes Don’t Return Pixel Information

Article: Q43914
Product(s): See article
Version(s): 5.10
Operating System(s): MS-DOS
Keyword(s): ENDUSER | s_quickc | mspl13_c
Last Modified: 11-JAN-1990

After a call to _getvideoconfig () from text modes, the structure
videoconfig contains zero (0) for numxpixels, numypixels, and
bitsperpixel. This is expected behavior because only the graphics
modes return pixel information.

Both text and graphics modes return information about the number of
text columns and rows.

The following example demonstrates the absence of pixel information
in text modes. The name of each text mode begins with "_TEXT."

#include stdio.h
#include graph.h

struct videoconfig vc;  /* variable vc of type videoconfig */

/* define an array of video modes and mode names
   since the numbers are not continuous */

int modes[12] = {_TEXTBW40, _TEXTC40, _TEXTBW80, _TEXTC80,
    _MRES4COLOR, _MRESNOCOLOR, _HRESBW, _TEXTMONO,
    _MRES16COLOR, _HRES16COLOR, _ERESNOCOLOR, _ERESCOLOR};

char *modenames[] = {"TEXTBW40", "TEXTC40", "TEXTBW80",
                      "TEXTC80", "MRES4COLOR", "MRESNOCOLOR",
                      "HRESBW", "TEXTMONO", "MRES16COLOR",
                      "HRES16COLOR", "ERESNOCOLOR", "ERESCOLOR"};s0
main()
{

   int i;
   /* test all video modes */
   for (i=0; i<= 11; i++) {
       _setvideomode (modes[i]);
       _getvideoconfig (&vc);
       printf ("\n video mode: \t%s\n",modenames[i]);
       printf (" x pixels: \t%d\n",vc.numxpixels);
       printf (" y pixels: \t%d\n",vc.numypixels);
       printf (" text columns: \t%d\n",vc.numtextcols);
       printf (" text rows: \t%d\n",vc.numtextrows);
       printf (" # of colors: \t%d\n",vc.numcolors);
       printf (" bits/pixel: \t%d\n",vc.bitsperpixel);
       printf (" video pages: \t%d\n",vc.numvideopages);
       printf (" Hit return for next video mode");
       getchar();
       _clearscreen (_GCLEARSCREEN);
   }
   _setvideomode (_DEFAULTMODE);
}

The definition of structure videoconfig and the arguments to
_setvideomode() are contained in the include file graph.h. The
arguments for _setvideomode() are also present on Page 539 of the
"Microsoft C for the MS-DOS Operating System: Run-Time Library
Reference."