How references are handled in memory

Question

class B {
};

class A {
    A(B& b):_b(b)  
    B& _b;
};

int main() {
    B b;
    A a(b);
    char* x = reinterpret_cast<char*>(&a);
}

I'm creating a hash function based on the byte values of the objects. I want to know wether the bytes of object a will hold b or will they hold a reference (pointer)?

See [this list of recommended books on C++](http://stackoverflow.com/q/388242/253056). — Paul R, Aug 09 '16 at 09:13
Objects don't have byte values. Two different byte arrays may well represent the same object value. How references are represented is implementation defined. — n. 1.8e9-where's-my-share m., Aug 09 '16 at 09:16

Some programmer dude · Accepted Answer · 2016-08-09T09:12:01.147

1

As you declared A::_b as a reference, it will "hold" a reference. Thus the object a does not contain the data of b if you examine a byte-wise.

By the way you forgot to use the address-of operator in your cast.

edited Aug 09 '16 at 09:12

answered Aug 09 '16 at 09:10

Some programmer dude

380,411
33
383
585

1

... however, any access to `_b` (by name) will be as if you were accessing the referent, so this may not matter for a hash function. – Lightness Races in Orbit Aug 09 '16 at 09:10
and for the same refered b object, the bytes of A will always be the same? – mkmostafa Aug 09 '16 at 09:11
@mkmostafa That depends on how references are implemented by the compiler. – Some programmer dude Aug 09 '16 at 09:12
1

ok. so it's not safe to hash based on the bytes if you have references. Since you might end up with two different hashes for two objects holding the same references? – mkmostafa Aug 09 '16 at 09:14
@mkmostafa Thats correct. Pointers are guaranteed to work though, but then you would be hashing the pointer and not the data it points to. – Some programmer dude Aug 09 '16 at 09:16
yea I was looking for some way to generically hash objects and that was the best that I could come up with so far (without using any external libs) :) – mkmostafa Aug 09 '16 at 09:17

How references are handled in memory

1 Answers1