Computer system

Difference between Structure and Union

Structure Union

For defining structure use
1 For defining union we use union keyword
struct keyword.

Structure occupies more
2 Union occupies less memory space than Structure.
memory space than union.

In Structure we can access
3 all members of structure at a In union we can access only one member of union at a time.
time.

Structure allocates separate Union allocates one common storage space for its all
4 storage space for its every members. Union find which member need more memory
members. than other member, then it allocate that much space

Bit‐Fields

Syntax
struct {

type [member_name] : width ;

};

The following table describes the variable elements of a bit field −

Elements Description


type An integer type that determines how a bit-field's value is interpreted.
The type may be int, signed int, or unsigned int.


member_name The name of the bit-field.


width The number of bits in the bit-field. The width must be less than or equal
to the bit width of the specified type.



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,The variables defined with a predefined width are called bit fields. A bit field can hold more
than a single bit; for example, if you need a variable to store a value from 0 to 7, then you can
define a bit field with a width of 3 bits as follows −

struct {

unsigned int age : 3;

} Age;

The above structure definition instructs the C compiler that the age variable is going to use only
3 bits to store the value. If you try to use more than 3 bits, then it will not allow you to do so. Let
us try the following example –

#include <stdio.h>

#include <string.h>

struct {

unsigned int age : 3;

} Age;

int main( ) {

Age.age = 4;

printf( "Sizeof( Age ) : %d\n", sizeof(Age) );

printf( "Age.age : %d\n", Age.age );

Age.age = 7;

printf( "Age.age : %d\n", Age.age );

Age.age = 8;

printf( "Age.age : %d\n", Age.age );

return 0;

}

Output

Sizeof( Age ) : 4

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, Age.age : 4

Age.age : 7

Age.age : 0

typedef
The typedef is a keyword that allows the programmer to create a new data type name for an
existing data type. So, the purpose of typedef is to redefine the name of an existing variable type.

Syntax

typedef datatype alias_name;

Example of typedef

#include<stdio.h>

#include<conio.h>

typedef int Intdata; // Intdata is alias name of int

void main()

{

int a=10;

Integerdata b=20;

typedef Intdata Integerdata; // Integerdata is again alias name of Intdata

Integerdata s;

clrscr();

s=a+b;

printf("\n Sum:= %d",s);

getch();

}

Output

Sum: 20


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