c++ vector of bitset pass to a function

Question

I want to implement an algorithm in C++ that needs a dynamically assigned huge vector of bitset (512x18,000,000 bits - I have 16Gb of RAM).

a) This works fine

int nofBits=....(function read from db);
vector < bitset <nofBits> > flags;
flags.resize(512);

but how do I pass it (by reference) to a function? Keep in mind, I do not know nofBits in compile time.

I could use a

vector<vector<bool> > 

but would not it be worse in terms of memory usage?

Answer 1

I had that same problem recently, however just like a std::array you need to know the size of the bitset at compile-time, since it's a template parameter. I found boost::dynamic_bitset as an alternative, and it worked like a charm.

Answer 2

std::vector<bool> is specialised to use memory efficiently. It is roughly as space efficient as std::bitset<N> (a few extra bytes because its size is dynamic and the bits live on the heap).

Note, however, that std::vector<bool> has issues, so tread lightly.