C++11新特性std::tuple的使用方法

更新時間：2020年10月06日 09:28:22 作者：半杯茶的小酒杯

這篇文章主要介紹了C++11新特性-std::tuple的使用方法，文中通過示例代碼介紹的非常詳細，對大家的學習或者工作具有一定的參考學習價值，需要的朋友們下面隨著小編來一起學習學習吧

1. 引入頭文件

#include <tuple>

2. std::tuple初始化

std::tuple<int, std::string, float> t1(10, "Test", 3.14);

這里要注意，不是所有的C++ 11編譯器都支持copy-list-initialization的方式。如下代碼所示。

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可以將它的元素逐個打印出來，不過非常繁瑣，我們可以通過如下通用的打印函數，幫助我們一次性的將tuple的所有要素打印出來。

#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);
}

輸出：

(10, Test, 3.14)

4、合并多個std::tuple

std::tuple_cat函數可以將多個std::tuple合并為一個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);
}

輸出：

(10, Test, 3.14, Foo, bar, 10, Test, 3.14, 42)

5. std::tuple的解包(unpack)

std::tie能夠將std::tuple包含的要素解包(unpack)成單個的對象。

#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;
}

輸出:

score:3.8, grade:A, name:Lisa Simpson

std::tie還支持std::pair對象的解包(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;
}

輸出:

score:3.8, name:Lisa Simpson

當我們不關注tuple中的某個元素時，可以使用std::ignore忽略該元素。

#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;
}

輸出: