C++11新特性std::tuple的使用方法

时间：2020-10-06来源：www.pcxitongcheng.com作者：电脑系统城

1. 引入头文件

1	`#include <tuple>`

2. std::tuple初始化

1	`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。

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6 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。

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42 #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。

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8 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。

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16 #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)。

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16 #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。

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16 #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;
}

C++11新特性std::tuple的使用方法

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