Write a c program to find the size of structure without using sizeof operator




How to find size of structure data type without using sizeof operator in c programming language  


#include<stdio.h>

struct student{
    int roll;
    char name[100];
    float marks;
};

int main(){

  struct student *ptr = 0;

  ptr++;
  printf("Size of the structure student:  %d",ptr);

  return 0;
}



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6 comments:

Rajiv kashyap said...

Can any1 please explain above program????

5/8/13, 12:08 PM
Tim said...

when you create pointer to structure lets say

struct student *ptr;

it will assign some memory address to its members such that

address of-

&ptr->roll 36857 the starting address
&ptr->name 36859 ( 36857 the starting address of roll + 2 bytes = 36859 the starting address of char name[100];)
&ptr->marks 36959 ( 36859 the starting address of name + 100 bytes = 36959 the starting address of float marks;)

so the address range for all members are 36857-36962 (coz the address range of marks is 36959 -36962 which is of 4 bytes).

ok now if you use statement as following like in above example

struct student *ptr=0;


it will assign starting address to 0 (zero) instead of 36857 such that

address of-

&ptr->roll 0
&ptr->name 2
&ptr->marks 102

so the address range of all members of structure will be now from 0 to 105 ( because marks will be stored at address 102-105 which is 4 bytes)

so ptr++ will increment to the starting address 106 of next structure variable which is equal the total size of structure.

hope this helps ...

8/11/15, 3:17 PM
Unknown said...

Thanks Tim

7/20/19, 12:07 PM
jay said...

the address range for char 102 to 105. how 105 is coming (adding 3 bytes more). Can anyone please explain??

9/1/19, 8:27 AM
Darshi said...

What will be the output of this program?plz tell any1

12/31/20, 8:18 PM
Anonymous said...

When we increment the pointer then pointer increases a block of memory (block of memory depends on pointer data type). So here we will use this technique to calculate the size of a structure.

1/23/21, 5:14 PM

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