C++ Anyway to access data members without knowing name

Question

So If I have a struct as follows:

struct MyObject {
    int x;
    int y;
};

Is there any way to get or manipulate MyObject's data members WITHOUT knowing their name?

In other words, achieving the same thing as:

MyObject.x = 10;

, but given that I don't know that MyObject has data member named x..

So something like this:

MyObject[0] = 10;  // x = MyObject's first data member....
MyObject[1] = 20;  // y = MyObject's second data member....

It isn't clear: if OP only needs to set them quantdev's linked answer is the solution. If they need to be read as well, it isn't. The question does say "get or manipulate" ... — Useless, Jul 25 '14 at 15:47
Use a `(void*)` pointer to its address, then increment/decrement it using `sizeof` to read. — vsoftco, Jul 25 '14 at 15:48
@vsoftco PODs can still be padded! You can only get at the first element this way (i.e. via a simple cast, but no offset). — BoBTFish, Jul 25 '14 at 15:50
Check out [`std::tuple`](http://en.cppreference.com/w/cpp/utility/tuple) — Captain Obvlious, Jul 25 '14 at 15:52
you could just randomly blast all memory around and maybe affect `MyObject.x` — Paul Evans, Jul 25 '14 at 15:53

score 0 · Answer 1 · answered Jul 25 '14 at 15:52

0

You can use an anonymous union

Union u {
    Myobject obj;
    Int a[2];
};

// U.a[0] corresponds to u.obj.x
// U.a[1] corresponds to u.obj.y
//

Note that i believe obj must be POD for this to work.

answered Jul 25 '14 at 15:52

tohava

score 0 · Answer 2 · answered Jul 25 '14 at 15:53

0

void func(void* data)
{
    int* a = (int*) data;
    *a++ = 10;
    *a++ = 20;
}

would change an object. But IMHO you are way lost studing "instances vs classes"

answered Jul 25 '14 at 15:53

Exceptyon

2 Answers2