Open file into array of bits in C++

One of the problems with std::bitset is you have to template the size. You can just read it in manually though...

char c;
vector<char> bytes;
int nread = 0;

while( in.get(c) )
{
    if( nread == 0 ) bytes.push_back(0);
    bytes.back() = (bytes.back() << 1) | (c ? 1 : 0);
    nread = (nread + 1) % 8;
}

#include <bitset>
#include <sstream>
#include <iostream>
#include <cinttypes>

namespace my
{
    template<size_t S> 
    std::istream &operator >> (std::istream &is, std::bitset<S> &bits)
    {
        std::uint8_t byte;
        size_t i = 0;
        while(i < S && (is >> byte))
            for(size_t j = 0; j < 8 && i < S; ++j)
                bits[i++] = (byte >> j) & 1;
        return is;
    }
}

int main()
{

    constexpr size_t bytes = 2;
    std::string bit_string("\x00\xFF", bytes);
    std::istringstream bit_stream(bit_string);

    std::bitset<8 * bytes> b;

    {
        using namespace my;
        bit_stream >> b;
    }

    std::cout << b << std::endl;

    for(size_t i = 0; i < b.size(); ++i)
        std::cout << b[i];

    std::cout << std::endl;
}

output:

1111111100000000
0000000011111111

run live:

http://ideone.com/Is7xRy

notes:

• bitset size is a non-type template parameter. You can't set it at runtime. So, this will only work with preallocation of the bitset and you'll get 0 padding for a larger bitset.
• If you want a runtime sized bitset, check out boost::dynamic_bitset.
• The sample is expected to work for files just by replacing istringstream by ifstream appropriately .