Bit Array in C++

Question

When working with Project Euler problems I often need large (> 10**7) bit array\'s.

My normal approach is one of:

bool* sieve = new bool[N];

bool sieve[         


        

Answer 1

You could look up std::bitset and std::vector. The latter is often recommended against, because despite the vector in the name, it doesn't really act like a vector of any other kind of object, and in fact doesn't meet the requirements for a container in general. Nonetheless, it can be pretty useful.

OTOH, nothing is going to (at least dependably) store 1 million bool values in less than 1 million bits. It simply can't be done with any certainty. If your bit sets contain a degree of redundancy, there are various compression schemes that might be effective (e.g., LZ*, Huffman, arithmetic) but without some knowledge of the contents, it's impossible to say they would be for certain. Either of these will, however, normally store each bool/bit in only one bit of storage (plus a little overhead for bookkeeping -- but that's usually a constant, and on the order of bytes to tens of bytes at most).