C - Programming

You can see its segment address is not changing. In relational operation whole far address is compared.

Physical Address Calculation

(13)How we can calculate actual memory address if we know segment and offset address ?
Ans:
Physical address =segment address * 16 + offset address; (in decimal)
Physical address =segment address * 0x10 + offset address; (in hexadecimal)

e.g
Let far address is 0x59994444 (in c hexadecimal integer constant has prefix 0x);
offset address is 0x4444
segment address is 0x5999
temp=segment address *0x10
=0x59990 (trick : only write one 0 to the right side )
=0x9990 (since offset address can have only for hexadecimal digit ,so remove the last digit)
Physical address =temp+offset address
=0x9990+0x4444
=0x0DDD4 (physical address are 20 bit so it is represented in 5 hexadecimal digit)
Process of conversion of 32 bit far address into 20 bit physical address is called normalization.

Note: It is possible that two different far address can represent same physical address

Huge Pointers

(13)What is huge pointer ?
Ans :
Is is 32 bit pointer .Its is similar to far pointer but any arithmetic or relational operation is performed in huge address then first it is normalize.
What will be output:
void main()
{
int huge *a=(int huge *)0x59990005;
int huge *b=(int huge *)0x59980015;
if(a==b)
printf("power of pointer");
else
printf("power of c");
getch();
}
Output: power of pointer
Explanation:
Here we are performing relational operation between two huge address. So first both a and b will normalize.
a=(0x5999)* (0x10)+(0x0005)=0x9990+0x0005=0x9995
b=(0x5998)* (0x10)+(0x0015)=0x9980+0x0015=0x9995
Here both huge address is representing same physical address. So a==b is true.
Note. Two 32 bit address can be represent same physical address but two physical address must be unique.

How will we Read Complex pointers

Rule 1. Give the first priority to the name (identifier) of pointer variable.
Rule 2. Give the least priority of to the data type with modifier (like int,char,float,unsigned int,static int etc.)
Rule 3. () and [] operator has higher priority (associativity left to right ) than * ,& (associativity right to left)
Priority: It means operator which have highest priority will execute first.
Associativity: If associativity is left to right and two operator have same priority then left most operator will have more priority and vice versa.
(to read the priority and associativity of each operator click here)
How to read
If right side of name (identifier) is ( ) then read function after the function read all as return type
Read [ ] operator array and after this read as it contain
Read * pointer if you have not encounter function or array otherwise read address.
If you will read example then you will understand more easily.

Example 1.
Read the pointer
int (*ptr)();

Ans:
Give first priority to ptr :1

There are two () operator ,associativity of () operator is left to right so left most operator will have more priority.

Left most ( ) operator will execute first . So give * to the second priority and right most ( ) operator to the third priority.
Give fourth priority to int

Read : ptr is pointer to such function which return type is integer data type.
Program:
#include
#include
void main()
{
int (*ptr1)();
int (*ptr2)();
void (*ptr3)();
ptr1=puts;
ptr2=getch;
ptr3=clrscr;
(*ptr3)();
(*ptr1)("POWER OF POINTER");
(*ptr2)();
Output: POWER OF POINTER
Example 2.
char *arr [3];
Ans :

arr is array of size 3 which contain address of char
program:
void main()
{
char *arr[3];
char a=1,b=2,c=3;
arr[0]=&a;
arr[1]=&b;
arr[2]=&c;
clrscr();
printf("%u %u",&b,arr[1]);
printf("\n%d",*arr[2]);
getch();
}
Output :
any addresss same address
3

Example 3
char (*ptr)[5];

Ans:

ptr is pointer to array of size 5 which contain char data type.
Program:
#include
#include
void main()
{
char arr[5]={1,2,3,4,5};
char (*ptr)[5];
ptr=&arr;
ptr=(*ptr)+2;
clrscr();
printf("%d",**ptr);
getch();
}
Output: 3
Example 4
unsigned long int ( * avg ())[ 3]
Program:

Ans:

avg is such function which return type is address of array of size of 3 which contain unsigned long int data type.
Program:
#include
#include
unsigned long int (* avg())[3]
{
static unsigned long int arr[3]={1,2,3};
return &arr;
}
void main()
{
unsigned long int (*ptr)[3];
ptr=avg();
clrscr();
printf("%d",*(*ptr+2));
getch();
}