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Pranav Jituri
Pranav Jituri

Reputation: 823

Getting Wrong Size Of The Structure After Compilation for the character Datatype

I have written a simple structure program. Here is the code of the program which I have written to print the size of the variables declared inside the structure-

#include<stdio.h>

main()
{
struct book
    {char name[10];
     int pages;
     float price;
    }b1={"Blue",500,200.00};
printf("The Address Of Name Is = %d ",&b1.name);
printf("\nThe Address Of Pages Is = %d",&b1.pages);
printf("\nThe Address Of Price Is = %d",&b1.price); 

}

Now the problem arises when I Compile the program and run it. I get the size of the CHARACTER array printed as 12 bytes instead of the 10 bytes. Here is the output -

blueelvis@Blueelvis:~$ ./a.out
The Address Of Name Is = 1264893904 
The Address Of Pages Is = 1264893916
The Address Of Price Is = 1264893920

Could someone please explain why this is happening? Also note that I am running in Linux environment.

Upvotes: 0

Views: 109

Answers (1)

Salgar
Salgar

Reputation: 7775

This is because of Data Structure Alignment which means that the compiler will insert padding between variables in a class/struct to make sure that the next variable falls on an optimal boundary for memory access. This is different for each type.

There is a full explanation here in this answer: Why isn't sizeof for a struct equal to the sum of sizeof of each member?

But for your case, the alignment of an integer is 4, so it rounds your 10 up to 12. i.e. there is padding between the char[] and the int to make sure the integer starts on a 4 byte boundary.

Upvotes: 1

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