//运行期以索引获取tuple元素-C++17 //需支持C++17及以上标准的编译器,VS2017 15.5.x、CodeBlocks 16.01 gcc 7.2 //参见:http://purecpp.org/?p=1581 #include <iostream> #include <tuple> using namespace std; template <size_t Idx, typename T> void visit(T& tup, size_t i) { if (i == Idx) cout << get<Idx>(tup) << endl; } //template <typename Tuple, size_t... Idx> //void visit(size_t i, Tuple& tp, index_sequence<Idx...>) //{ // (visit<Idx>(tp, i), ...); //} template <class Tuple, size_t...Idx> void visit1(size_t i, Tuple& tp, index_sequence<Idx...>) { ((i == Idx && (visit<Idx>(tp, i), false)), ...); } template <typename Tuple> void visit_help(size_t i, Tuple& tp) { //visit(i, tp, make_index_sequence<tuple_size<Tuple>::value>{}); visit1(i, tp, make_index_sequence<tuple_size<Tuple>::value>{}); } int main() { auto tp = make_tuple(45, "The test", true); int i = 1; visit_help(i, tp); //The test return 0; }