c++ - Logic behind a function -

i want understand function does, logic behind it.

i've searched every term on own (ex: size_t, bitset...) still want know how logic flows?

size_t popcount(size_t n) {     std::bitset<sizeof(size_t) * char_bit> b(n);     return b.count(); } 

returns number of bits in bitset b set (i.e. have value of 1).

size_t popcount(size_t n)  

passes n number of bits set in bitset.

std::bitset<sizeof(size_t) * char_bit> b(n); 

creates std::bitset

return b.count(); 

check documentation std::bitset see std::bitset::count returns , answers question. see std::bitset standard library provided template class storing bits.once understand rest pretty loking in documentation know functionality class provides , mapping how code uses it.