C programming Interview questions and answers: 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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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

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