Pointer to array of Structures , Size of Pointer (Pointer last topic or Part 5)

 

              Pointer to array of structures:

 

struct employee emp[5];

 

struct employee *ptr;

 

ptr=emp;à value = base address = 1000

 

ptr++ è ptr = ptr+1 à 1000+1*51 = 1051

ptr++ = 1051 + 1*51 = 1102

ptr++ = 1102+1*51 = 1153

ptr++ = 1153 + 1*51 = 1204

 

For variable way of accessing is by using   dot  ( . ) operator

eg:

            emp.empNum;

 

for pointer  variable way of accessing is by using   arrow ( à ) operator

 

     ptràempNum;

 

 

pointer to pointer :

 

int a=10;

int *ptr1=&a;à pointer to variable

int  **ptr2=&ptr1;à pointer to pointer.

 

Eg:

            int a=10;

int *ptr1=&a;

int  **ptr2=&ptr1;

 

            printf(“\n %d “,a); à o/p : 10

            *ptr1=20;

            printf(“\n %d “,a); à o/p : 20

            **ptr2=30;

printf(“\n %d “,a); à o/p : 30

 

 

#include<stdio.h>

int main()

{

  int a=10;

  int *ptr1=&a;

  int **ptr2=&ptr1;

  float *fp;

            printf("\n%d %u  %u ",a,ptr1,ptr2);

            printf("\n%u  %u  %u",&a,ptr1,*ptr2);

            printf("\n%u  %u  %u ",&ptr1,ptr2, &ptr2);

 

printf("\n%d %d  %d",sizeof(ptr1),sizeof(ptr2),sizeof(fp));

 

  return 0;

}

                 Size of  a pointer

 

1. Size of pointer is not depending on data type.

 

2. Pointer contains address, which is an unsigned int.

 

3. Since size of unsigned int is 2 bytes, size of pinter is also 2 bytes.

 

4. Size of pointer depends compiler.

 

5. As per 32 bit compile size of int is 2 bytes, hence size pointer also 2 bytes.

 

6. As per 64 bit compile size of int is 4 bytes, hence size pointer also 4 bytes.

 

7. Type of the pointer, gives instruction, how many bytes has to read from the memory.

 

Program to check size of pointer:

 

#include<stdio.h>

#include<conio.h>

int main()

{

 

   int a=10;

   float b=20.5;

   char ch='x';

int *ip;

   float *fp;

   char *cp;

   clrscr();

   ip=&a;

   fp=&b;

   cp=&ch;

 

   printf("\n%d %f %c",*ip,*fp,*cp);

   printf("\n%d %d %d",sizeof(ip),sizeof(fp),sizeof(cp));

   return 0;

}

Note: All the programs given here are pre compiled and pre runned. If the viewer has any doubt about these they are free to run the compiler provided after each program.