Question

I have a vector<set<char> > data structure (transactions database) and I want to know the size of it. When I use sizeof() with each set<char> the size is 24 in spite of the set contains 3, 4 or 5 chars. Later, when I use sizeof() with the vector<set<char> > the size is 12… I suppose this is not the way to know the size of a data structure. Any help?
Thanks.

Answer 1

You want vector::size() and set::size().

Assuming v is your vector, do this:

size_t size = 0;
for (vector<set<char> >::const_iterator cit = v.begin(); cit != v.end(); ++cit) {
    size += cit->size();
}

sizeof() is giving you the in-memory size of the object/type it is applied to, in multiples of sizeof(char) (usually one byte). If you want to know the in-memory size of the container and its elements, you could do this:

sizeof(v) + sizeof(T) * v.capacity(); // where T is the element type