1. 引入头文件
#include <tuple>
2. std::tuple初始化
std::tuple<int, std::string, float> t1(10, "Test", 3.14);
这里要注意，不是所有的C++ 11编译器都支持copy-list-initialization的方式。如下代码所示。
std::tuple<int, int> foo_tuple() { return {1, -1}; // Error until N4387 return std::tuple<int, int>{1, -1}; // Always works return std::make_tuple(1, -1); // Always works}
3. 打印std::tuple
打印std::tuple可以将它的元素逐个打印出来，不过非常繁琐，我们可以通过如下通用的打印函数，帮助我们一次性的将tuple的所有要素打印出来。
#include <iostream>#include <tuple>#include <string> // helper function to print a tuple of any sizetemplate<class Tuple, std::size_t N>struct TuplePrinter { static void print(const Tuple& t) { TuplePrinter<Tuple, N-1>::print(t); std::cout << ", " << std::get<N-1>(t); }}; template<class Tuple>struct TuplePrinter<Tuple, 1> { static void print(const Tuple& t) { std::cout << std::get<0>(t); }}; template<typename... Args, std::enable_if_t<sizeof...(Args) == 0, int> = 0>void print(const std::tuple<Args...>& t){ std::cout << "()\n";} template<typename... Args, std::enable_if_t<sizeof...(Args) != 0, int> = 0>void print(const std::tuple<Args...>& t){ std::cout << "("; TuplePrinter<decltype(t), sizeof...(Args)>::print(t); std::cout << ")\n";}// end helper function int main(){ std::tuple<int, std::string, float> t1(10, "Test", 3.14); print(t1);}
输出：
(10, Test, 3.14)
4、合并多个std::tuple
std::tuple_cat函数可以将多个std::tuple合并为一个tuple。
int main(){ std::tuple<int, std::string, float> t1(10, "Test", 3.14); int n = 7; auto t2 = std::tuple_cat(t1, std::make_tuple("Foo", "bar"), t1, std::tie(n)); n = 42; print(t2);}
输出：
(10, Test, 3.14, Foo, bar, 10, Test, 3.14, 42)
5. std::tuple的解包(unpack)
std::tie能够将std::tuple包含的要素解包(unpack)成单个的对象。
#include <iostream>#include <tuple>#include <string>int main() { auto info = std::make_tuple(3.8, 'A', "Lisa Simpson"); double score = 0.0; char grade; std::string name; std::tie(score, grade, name) = info; std::cout << "score:" << score << ", grade:" << grade << ", name:" << name << std::endl;return 0;}
输出:
score:3.8, grade:A, name:Lisa Simpson
std::tie还支持std::pair对象的解包(unpack)。
#include <iostream>#include <tuple>#include <string>#include <utility>int main() { auto info = std::make_pair(3.8, "Lisa Simpson"); double score = 0.0; std::string name; std::tie(score, name) = info; std::cout << "score:" << score << ", name:" << name << std::endl;return 0;}
输出:
score:3.8, name:Lisa Simpson
当我们不关注tuple中的某个元素时，可以使用std::ignore忽略该元素。
#include <iostream>#include <tuple>#include <string>#include <utility>int main() { auto info = std::make_pair(3.8, "Lisa Simpson"); double score = 0.0; std::string name; std::tie(score, std::ignore) = info; std::cout << "score:" << score << ", name:" << name << std::endl;return 0;}
输出:
score:3.8, name:
参考材料
https://en.cppreference.com/w/cpp/utility/tuple/tuple_cat
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