Question

I have a function to print characters on the screen that is like this:

void print(int colour, int y, int x, const char *string)
{
   volatile char *video=(volatile char*)0xB8000 + y*160 + x*2;
   while(*string != 0)
   {
      *video=*string;
      string++;
      video++;
      *video=colour;
      video++;
   }
}

And I want to print the character 254 in decimal, but I need to use stored on a const char*. I can t try print(0x0F, 0, 0, 0xFE);, because this trows a error of pointer without cast, then how can I do this?

Answer 1

Embed the character in the string using C s hex notation:

print(0x0f, 0, 0, "xfe");

As folks have pointed out, you might want to pretty up the code a bit, perhaps by adding a symbolic name for the VGA framebuffer base address.

Answer 2

This is off-topic, memories of this, but digging up the code I found this:

/* Global Variables */
static Word far *ScrPtr;

/* Local Variables */
static Word VidSeg;
...

int WinScreenHeight(void)
{
    return (*(unsigned char far *) 0x484) + 1;
}

int WinScreenWidth(void)
{
    return (*(unsigned int far *) 0x44A);
}

void WinInit(){
   SetMode(AdapterType());
   ScrPtr = (Word far *) CreateFarPtr(VidSeg, 0x0000);
}

static void SetMode(int VideoAddress)
{
    switch(VideoAddress)
    {
        case VGA :
        case MCGA:
        case EGA :
        case CGA :  (Word) VidSeg = 0xB800;
                    break;
        case MDA :  (Word) VidSeg = 0xB000;
                    break;
        case  ?  :  fprintf(stderr, "Sorry Unknown Video Adapter.
");
                    fprintf(stderr, "This program requires C/E/MC/VGA, Mono Adapter
");
                    exit(1);
    }
}
static int AdapterType(void)
{
    char far *VidMode;
    char blreg, alreg;
    VidMode = (char far *) 0x00000449L;
    asm mov ax, 0x1a00;
    asm push bp;
    asm int 0x10;
    asm pop bp;
    asm mov blreg, bl;
    asm mov alreg, al;
    if (alreg == 0x1a && blreg >= 9) return(MCGA);
    if (alreg == 0x1a && blreg >= 7 && blreg <= 9) return(VGA);
    if (blreg == 4 || blreg == 5) return(EGA);
    if (*VidMode == 3) return(CGA);
    if (*VidMode == 7) return(MDA);
    return( ? );
}

Hope this helps, Best regards, Tom.

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