How does c++ sizeof works?

Asked Oct 01 '17 at 10:45

Active Oct 01 '17 at 10:45

Viewed 48 times

I have following code :

#include <iostream>
using namespace std;
class A {
    int a;
    char* b;
};

class B {
    int a;
};

class C {
    char *b;
};

int main() {
    // your code goes here
    cout << "size of A:" << sizeof(A) << endl;
    cout << "size of B:" << sizeof(B) << endl;
    cout << "size of C:" << sizeof(C) << endl;
    return 0;
}

link to ideone : https://ideone.com/OAQuMv

Size of A is 16

Size of B is 4

Size of C is 8

Why size of A is 16 not 12?

asked Oct 01 '17 at 10:45

pZCZ

1

Sizes of fundamental types depend on the platform. Sizes of structs depend on the compiler and options, since the compiler can add padding for efficiency. – Cheers and hth. - Alf Oct 01 '17 at 10:48
I suspect it is because of alignment, the char * starting upon a multiple of 8 bytes. Ty swap int a and char *b in class A. Is the result the same? – Jacques de Hooge Oct 01 '17 at 10:50
yes the result is the same. – pZCZ Oct 01 '17 at 10:53

How does c++ sizeof works?

0 Answers0