Is this a violation of strict aliasing rules? [duplicate]

Question

Regardless of how 'bad' the code is, and assuming that alignment etc are not an issue on the compiler/platform, is this undefined or broken behavior?

If I have a struct like this :-

struct data
{
    int a, b, c;
};

struct data thing;

Is it legal to access a, b and c as (&thing.a)[0], (&thing.a)[1], and (&thing.a)[2]?

In every case, on every compiler and platform I tried it on, with every setting I tried it 'worked'. I'm just worried that the compiler might not realize that b and thing[1] are the same thing and stores to 'b' might be put in a register and thing[1] reads the wrong value from memory (for example). In every case I tried it did the right thing though. (I realize of course that doesn't prove much)

This is not my code; it's code I have to work with, I'm interested in whether this is bad code or broken code as the different affects my priorities for changing it a great deal :)

Tagged C and C++ . I'm mostly interested in C++ but also C if it is different, just for interest.

Answer 1

For c++: If you need to access a member without knowing its name, you can use a pointer to member variable.

struct data {
  int a, b, c;
};

typedef int data::* data_int_ptr;

data_int_ptr arr[] = {&data::a, &data::b, &data::c};

data thing;
thing.*arr[0] = 123;