Turbo C++ ... Segment Offset

[matias_beretta]

Well, I'm writing my realmode os with Turbo C++ and when I want to write to the video memory i have to:

asm push 0xb800;
asm pop es;
asm mov di, 0;
asm mov byte ptr es:[di], 'M'
asm inc di
asm mov byte ptr es:[di], 7
asm inc di

this writes M on the screen, but it is written in assembly

is there any way of accessing memory with a segment and an offset from C?

thanks

[raevin]

Well, I'm writing my realmode os with Turbo C++ and when I want to write to the video memory i have to:

asm push 0xb800;
asm pop es;
asm mov di, 0;
asm mov byte ptr es:[di], 'M'
asm inc di
asm mov byte ptr es:[di], 7
asm inc di

this writes M on the screen, but it is written in assembly

is there any way of accessing memory with a segment and an offset from C?

thanks

Have you looked at any of the beginner printf() functions various operating system development tutorials give you?

[JamesM]

Not AFAIK. Your best bet is to go into protected mode.

[jnc100]

There is nothing defined in the C standard for accessing memory via segments, because segments are pretty intel-specific. There are compiler-specific extensions however. I don't know about Turbo C++, but open watcom allows something like:

Code: Select all

__segment seg;
seg = 0xb800;
unsigned short int __based (seg) *dispmem;
dispmem[y * 80 + x] = ch | (attrib << 8);

Obviously its not portable, but then segments aren't anyway.

Regards,
John.

[Brynet-Inc]

Code: Select all

#define MK_FP( seg, off ) \
         ((void far *)(((unsigned long)(seg) << 16)|(unsigned)(off)))

unsigned char far *video_mem = (char far *)MK_FP(0xB800, 0x0000);

This "might" work under "Turbo C"..

I can't verify it will though, I simply used my google skills...

Good luck..

[frank]

You could create far_peek and far_poke functions in assembly.

[Combuster]

IIRC Turbo C has got MK_FP and several related functions predefined in one of its headers (include dos.h / io.h?). Since TC supports far pointers (seg:off pairs), you should be able to write directly to video memory without resolving to (inline) assembly.

TC3 does come with an extensive help system. You should look up the mentioned functions and headers to find the things you need.

[matias_beretta]

int main(void)
{
unsigned int far *screen;
*screen = MK_FP(0xb800, 0)
}

ERROR!!!: Nonportable pointer conversion in function main

What does it means???