pokeb help

[matias_beretta]

Hello, i'm trying to make a pokeb procedure without using inline assembly:

Code: Select all

void pokeb(unsigned segment, unsigned offset, char value)
{
    char far *ptr;
    ptr = (char far *)(segment * 16 + offset);
    *ptr = value;
}

but this isn't working and i can't work out a solution

[SpooK]

Hello, i'm trying to make a pokeb procedure without using inline assembly:

void pokeb(unsigned segment, unsigned offset, char value)
{
char far *ptr;
ptr = (char far *)(segment * 16 + offset);
*ptr = value;
}

but this isn't working and i can't work out a solution

Perhaps just "ptr = value" or maybe even "ptr[0] = value" since ptr is already casted as a pointer?

[Combuster]

char far *

far pointers?! Are you by any chance using Turbo C?

(if so, use the MK_FP macro)

[matias_beretta]

I'm using Turbo C++ 3.0, and i know it has pokeb and mk_fp. but i want to make my own includes.

I tested using ptr[0] or ptr instead of *ptr but it doesn't work...

I've seen that many people use: ptr = (char far *)(segment << 16) | offset);
but i don't understand why they use << 16 (to multiply the segment by 16 its possible to use segment << 4) and i don't understand why the use |...

[Combuster]

I don't have TC3 installed anymore, so I can't check. But it seems that if you cast a 32-bit int into a far pointer it will split it for you into a seg:off pair (2x16 bits = 32 bits)

Nevertheless, pokeb, MK_FP etc, are TC-specific macros (and are portable), so there's no need to reinvent the wheel when its given to you on a silver plate.