Question

While studying tsr programming i have seen the use of certain code which i cannot understand..

The example cede part is(in c):
(please explain the bolded sections)

#include "dos.h"
#include"stdio.h"
void interrupt our();
void interrupt (*prev)();
char far *scr=(char far*)0xB8000000L;
int ticks;
unsigned char color;
main()
{   
    prev=getvect(8);   // <<<<<
    setvect(8,our);    // <<<<<
    keep(0,10000);     // <<<<<
}

Answer 1

You would partially understand this code if you read the answer i posted to your similar question on TSR

How to write a TSR which changes case of characters

The most important things here are

Far pointer: Since 16 bit DOS used segment offset addressing scheme, your normal near pointer could not access memory beyond 64K of it’s allocated segment. You have to read details to understand it.

Video memory address: This B8000000 is the address for which you need far pointer. The special thing about this address is, that starting from this location bytes (equal to the resolution of screen * 2) are copied directly into video memory.

So if you assign a character to a pointer address after indirection it will be printed on screen

Something like

char * far p = 0xB8000000;

*p = 'a'; // this would actually print a on screen at left top

Loop forward to get to the rest of the screen.

There was a c book by yashwant kanetkar which had a good deal of reference for this. I remember using it in my undergrad many years ago.

The rest of them are just indexing api’s in dos.h. Why don’t you go through their description and get back here if you don’t understand any?