Use of sizeof() operator in C

The C compilaer provides an operator name sizeof() that is responsible to return memory space require in bytes. A sizeof() operator can accept a variable, datatype, object etc as an argument and returns a memory space required in byte.

Syntax:- To use sizeof() operator

Var = sizeof(var/datatype/object);

var = sizeof var/datatype/object;

var=  sizeof expression;

or

printf(“<format specifier>”,sizeof(var/datatype));

Example:-

void main()

{

int a,char ch;

clrscr();

printf(“Capacity of a =%d”,sizeof(a));

printf(“\n Capacity of ch=%d”,sizeof(ch));

printf(“\n long int =%d”,sizeof(long int));

printf(“\n short int=%d”,sizeof(short int));

printf(“\n float  =%d”,sizeof(float));

printf(“\n long float =%d”,sizeof(long float));

printf(“\n Double=%d”,sizeof(double));

printf(“\n  long Double=%d”,sizeof(long double));

getch();

}

OUTPUT-----à

     Capacity of a=2

     Capacity of ch=1

     long int=4

     short int=2

     float=4

     long float=8

     double= 8

     long double=10

Explanation:-

   (1)    In C language when we use a value between -32767 and 32767 then it by default promote into int datatype and if we exceed this range then value by default promote into long int.

Example:-

(a)    printf(“%d”,sizeof(2500));

ROUGH sizeof 25 * 3 = 2*3 =6

Output--à 2

(b)   printf(“%d”,sizeof 25*2);

Output---à 6

(c)    printf(“%d”,sizeof 40000);

Output---à 4

(d)   printf(“%d”,sizeof 25+5);

ROUGH sizeof -40*3%2 =2*3%2 =6%2 =0

Output---à 7

(e)   printf(“%d”,sizeof -40*3%2);

Output---à 0

    (2)    In C language, a fractional value by default promote into double and if we use symbol (F/f) with value then it promote into float.

Example:-

(a)    printf(“%d”,sizeof(4.5));

Output---à 8

(b)   printf(“%d”,sizeof 4.5f));

Output---à 4

(c)    printf(“%d”,sizeof 4.5-3);

ROUGH sizeof 2.8f- 2*5 =     4              10 =4-10 =-6

Output---à 5

(d)   printf(“%d”,sizeof 2.8f-2*5);

Output---à -6

(e)   printf(“%d”,sizeof ‘A’);

Output---à 2

(f)     char *p;

printf(“%d”,sizeof p);

Output---à 2

(g)    float *p;

printf(“%d”,sizeof p);

Output---à 2

NOTE—In C language, a pointer always allocates 2 bytes memory space.

Example:-  int num[3];

(a)    printf(“%d”,sizeof num[0]);

Output-----à 2

(b)   prinft(“%d”, sizeof  num);

Output---à 6