C Programming - Complicated Declarations - Discussion

What are near, far and huge pointers?

These are some old concepts used in 16 bit intel architectures in the days of MS DOS, not much useful anymore.

Near pointer is used to store 16 bit addresses means within current segment on a 16 bit machine. The limitation is that we can only access 64kb of data at a time.

A far pointer is typically 32 bit that can access memory outside current segment. To use this, compiler allocates a segment register to store segment address, then another register to store offset within current segment.

Like far pointer, huge pointer is also typically 32 bit and can access outside segment. In case of far pointers, a segment is fixed. In far pointer, the segment part cannot be modified, but in Huge it can be.

@Madhu.

First, let's understand how to read these.

Simple on:

char c; // c is a character.

char *ptr; // ptr is a pointer to a char.

char far *fptr; // fptr is a far pointer to char.

Remember when we write double points.

char **dptr; // dptr is a pointer to pointer to a char.

In a similar way.

char far *near *prt1; // prt1 is a near pointer to far pointer to char.

Hope it makes sense.

@All.

Here is my coding.

#include<stdio.h>
int main()
{
int *a;
float *b;
char *c;
double *d;
int i;
float j;
char k;
double l;
a=&i;
b=&j;
c=&k;
d=&l;
printf("%d",sizeof(a));
printf("%d",sizeof(b));
printf("%d",sizeof(c));
printf("%d",sizeof(d));
}


Output:888.

Associativity in pointer is right to left... so for
char far *near *ptr1;(think it is like type casting or pointer to pointer).
ptr1 will contain address of (*near) which will be 2 byte and that contain the address of far memory character so it will now 4 byte.
so the sizeof(ptr1)= 2 byte and sizeof(*ptr)= 4 byte.

Near pointers-refer to current segment $ point to 64kbytes, occupy 2bytes.

Far pointer-refer to data segment $ points to gigabyte, occupy 4 byte.

Huge pointer-similar to far pointers, but work slowpy, occupy 4 byte.

OUTPUT:

The output size is too large (infinite loop or larger text output).

This is the output when I compiled the above code in India bix compiler, and this does not match with the answer.

I can't understand the declarations how is it possible to make multiple declarations without being separated by comma.

char far, *near, *ptr1;

I think above declaration is only right.

GNU GCC v 4.8 compiler is showing error.

And GCC Compiler (32 Bit Linux Platform) of IndiaBix is showing "The output size is too large (infinite loop or larger text output)".

Why?

Near pointer is used to store 16 bit address.

Far pointer is used to store 32 bit addresses.

Huge pointer is used to store 32 bit addresses.

Byte allocation near-2, far, huge-4 so ptr1 refer near so 2bytes, ptr2, 3 refer far & huge so 4 bytes.