How to convert a range subset of bits in a C++ bitset to a number? -

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• in bitset, can use “to_ulong” specific range of bits? 1 answer

i have std::bitset , bitset type provides to_ulong method translate bitset number, problem translating bitset number while considering range in bitset, need implement own powerof2 function or there more standard approach ?

you can drop unnecessary bits like

#include <bitset> #include <iostream>  // drop bits outside range [r, l) == [r, l - 1] template<std::size_t r, std::size_t l, std::size_t n> std::bitset<n> project_range(std::bitset<n> b) {     static_assert(r <= l && l <= n, "invalid bitrange");     b >>= r;            // drop r rightmost bits     b <<= (n - l + r);  // drop l-1 leftmost bits     b >>= (n - l);      // shift place     return b; }  int main() {     std::bitset<8> b2(42); // [0,0,1,0,1,0,1,0]     std::cout << project_range<0,8>(b2).to_ulong() << "\n"; // 42 == entire bitset     std::cout << project_range<2,5>(b2).to_ulong() << "\n"; // 8, middle bit } 

live example output.