Different results in c++ using sizeof

Question

I'm facing a strange result sizeof() during testing. How T1 and T2 are the same size as the types used in T2 is smaller than T1?

#include <iostream>

using namespace std;

struct T1 {
    int     id;
    int     enable;
};

struct T2 {
    int     id;
    char    enable;
};


int main() {
    cout << sizeof(T1) << endl; // Print 8
    cout << sizeof(T2) << endl; // Print 8
    return 0;
}

Obviously, `T2` is not in fact smaller than `T1`. Read about [padding](http://en.wikipedia.org/wiki/Data_structure_alignment) — Igor Tandetnik, Dec 28 '14 at 18:46
Robo upvoters?!? I smell robo upvoters! Let's keep the low research efforts stuff out here please, for sake of the quality of SO. — πάντα ῥεῖ, Dec 28 '14 at 18:57

score 1 · Accepted Answer · edited Dec 28 '14 at 19:53

1

T2 is padded for alignment.

That is, it contains unused bytes such that an array of T2 will have all the T2.id dword aligned.

edited Dec 28 '14 at 19:53

Meninx - メネンックス

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answered Dec 28 '14 at 18:48

Jasen

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Different results in c++ using sizeof

1 Answers1