sortingWithPointerToMember.cpp

std::vector<Complex> vec = { { 3, 1},
                             { 1, 9 },
                             { 8, 2 },
                             { 3, 14 }};

double Complex::*var;
auto comparator = [&var](const Complex &a, const Complex &b) { return a.*var < b.*var; };

var = &Complex::real; //Sorting for real numbers
std::sort(vec.begin(), vec.end(), comparator);

var = &Complex::imaginary; //Sorting for imaginary numbers
std::sort(vec.begin(), vec.end(), comparator);