Are variables declared side by side in a struct contiguous?

Question

I know for sure that array elements are stored contiguously, but what if I declared something like this:

class A {
    public:
    int a, b, c;
    // or
    int a;
    int b;
    int c;
}

Are the members stored contiguously? I've been thinking if there's a possibility that a variable is stored in between the declaration of a and b from another process, so that it's not contiguous. But I'm not sure. Are there any guarantees?

FYI: http://stackoverflow.com/questions/4178175/what-are-aggregates-and-pods-and-how-why-are-they-special — , Nov 23 '16 at 09:03
Woop okay, i'll mark as duplicate thanks for the links. @n.m. because i tested it and the address is contiguous, so that confuses me a bit i guess. — Greffin28, Nov 23 '16 at 09:15
There's no possibility of another process "adding" variables to yours. — molbdnilo, Nov 23 '16 at 09:15
There is a leap of faith between "I have seen it happened once" and "this is guaranteed to happen always no matter what". — n. m. could be an AI, Nov 23 '16 at 09:22
FYI: http://stackoverflow.com/questions/289559/class-layout-in-c-why-are-members-sometimes-ordered — Werner Henze, Nov 23 '16 at 09:27
This question is about contiguity of class instance variables, not initialization order. @closevoters look again. — user207421, Nov 23 '16 at 09:56
I'm reasonably sure there's no semantic difference between `int a, b, c;` and `int a; int b; int c;` — Keith Thompson, Nov 23 '16 at 22:02

score 2 · Accepted Answer · answered Nov 23 '16 at 21:56

2

a b and c are guaranteed to be in that order in the struct.

However, in general, there might be structure padding in between any two struct members. Typically there would be no padding for a struct that only contained int members but it would be good practice to not make that assumption.

You could check this at compile-time:

static_assert( sizeof(A) == 3 * sizeof(int),  "oops, A had padding" );

answered Nov 23 '16 at 21:56

M.M

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Sorry for the late reply. Anyway thank you, i'll then try to avoid using it that way. – Greffin28 Feb 14 '17 at 13:16

Are variables declared side by side in a struct contiguous?

1 Answers1