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

A 'bool' type isn't stored using only 1 bit. From your comment about the size, it seems to use 1 entire byte for each bool.

A C like way of doing this would be:

uint8_t sieve[N/8]; //array of N/8 bytes

and then logical OR bytes together to get all your bits:

sieve[0] = 0x01 | 0x02; //this would turn on the first two bits

In that example, 0x01 and 0x02 are hexadecimal numbers that represent bytes.