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when a class is in the Heap, where are its members?

Started by draconar Dec 1, 2010 at 7:02 PM 0 replies 800+ views

Original Post

Dec 1, 2010 at 7:02 PM

hi,

a question that torments me for so much time.

Suppose I'm at the main() function and NEWed a class on the heap.

X x = new X;

and this X class holds inside itself many huge data structures like maps, sets, vectors, etc. But they are all declared like this

class X {
std::map< z, w> map;
std::vector< z> vec;

};

let's supposed they are filled and HUGE. Where are they located? in the Heap of the in the Stack?

Noggs

Dec 1, 2010 at 7:12 PM

The map and vec objects will be located on the heap at a small offset from X. The actual data inside the map and vector objects is allocated from the heap as well, but could be anywhere.

This is how your X class might be laid out in memory:

X + 0:                 mapX + sizeof(map<z,w>):  vec

If you do sizeof(map) in your debugger you will see how big that object is. That will never change regardless of how much data you store in it.

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