C Structure Concepts

1.#include < stdio.h > struct st {     int x;     struct st next; };    int main() {     struct st temp;     temp.x = 10;     temp.next = temp;     printf("%d", temp.next.x);        getchar();     return 0; }

Output: Compiler Error

A C structure cannot contain a member of its own type because if this is allowed then it becomes impossible for compiler to know size of such struct. Although a pointer of same type can be a member because pointers of all types are of same size and compiler can calculate size of struct.

Nesting of Structures

struct outer{

int a;

struct inner{

char c;

};

};

It is necessary to assign name of inner structure at the time of declaration other wise we cannot access the member of inner structure. So correct declaration is:

struct outer{

int a;

struct inner{

char c;

}name;

};

Structure & Bit Fields

1.void main()

{

struct employee

{

unsigned id: 8;

unsigned sex:1;

unsigned age:7;

};

struct employee emp1={203,1,23};

clrscr();

printf("%d\t%d\t%d",emp1.id,emp1.sex,emp1.age);

getch();

}

Output: 203 1 23

We can access the data member in same way.

How bit data is stored in the memory:

Minimum size of structure which data member in bit is two byte i.e. 16 bit. This is called word size of microprocessor. Word size depends on microprocessor. Turbo c is based on 8086 microprocessor which word size is two byte.

Bits are filed in from right to left direction 8 bit for id,1 bit for sex and 7 bit for age.

2.void main()

{

struct bitfield

{

unsigned a:5;

unsigned c:5;

unsigned b:6;

}bit;

char *p;

struct bitfield *ptr,bit1={1,3,3};

p=&bit1;

p++;

clrscr();

printf("%d",*p);

getch();

}

Output: 12

Explanation:

Binary value of a=1 is 00001 (in 5 bit)

Binary value of b=3 is 00011 (in 5 bit)

Binary value of c=3 is 000011 (in 6 bit)

In memory it is represented as:

Let address of bit1 is 500 which initialize to char pointer p. Since can is one byte data type so p++ will be 501. *p means content of memory location 501 which is (00001100) and its binary equivalent is 12. Hence output is 12.

 

3.void main()

{

struct bitfield

{

signed int a:3;

unsigned int b:13;

unsigned int c:1;

};

struct bitfield bit1={2,14,1};

clrscr();

printf("%d",sizeof(bit1));

getch();

}

Output: 4

 

4.void main()

{

struct bitfield

{

unsigned a:3;

char b;

unsigned c:5;

int d;

}bit;

clrscr();

printf("%d",sizeof(bit));

getch();

}

Output: 5

Note: (Actual output will 6 due to slack byte ,So Before executing this program first go to option menu then compiler then code generation then select word alignment then press OK)

 

5.void main()

{

struct field

{

int a;

char b;

}bit;

struct field bit1={5,'A'};

char *p=&bit1;

*p=45;

clrscr();

printf("\n%d",bit1.a);

getch();

}

Output: 45