C++11新特性std::tuple如何高效运用在复杂数据结构中？

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1. 引入头部文件

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 size template<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

en.cppreference.com/w/cpp/utility/tuple/tuple_cat

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