Rules for struct aligntment

Asked Mar 01 '18 at 18:13

Active Mar 01 '18 at 18:13

Viewed 37 times

Consider the code:

struct A
{
    char b;
    bool a;
    double c;
};

struct B
{
    char b;
    double c;
    bool a;
};

int main()
{
    std::cout << sizeof(A) << '\n'; // 16
    std::cout << sizeof(B) << '\n'; // 24
}

Whats happening here ? What are purposes in a second case to be aligned by a 8 bytes ??

(OS: windows 7 32 bit)

asked Mar 01 '18 at 18:13

ampawd

4

Try it on paper. Consider that the compiler can't reorganize those members. – François Andrieux Mar 01 '18 at 18:14
`double` requires 8-byte alignment. Remember that `sizeof` includes the padding. – Barmar Mar 01 '18 at 18:17
http://en.cppreference.com/w/cpp/language/object#Alignment – Justin Mar 01 '18 at 18:17

Rules for struct aligntment

0 Answers0