c++11 标准模板（STL）（std::tuple）（七）
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定义于头文件 <tuple>
|
template< class... Types > | (C++11 起) |
类模板 std::tuple 是固定大小的异类值汇集。它是 std::pair 的推广。
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若 (std::is_trivially_destructible_v<Types> && ...) 为 true ，则 | (C++17 起) |
模板形参
| Types... | - | tuple 所存储的元素的类型。支持空列表。 |
元组式访问指定的元素
std::get(std::tuple)
| template< std::size_t I, class... Types >
typename std::tuple_element<I, tuple<Types...> >::type& get( tuple<Types...>& t ) noexcept; | (1) | (C++11 起) (C++14 起为 constexpr) |
| template< std::size_t I, class... Types >
typename std::tuple_element<I, tuple<Types...> >::type&& get( tuple<Types...>&& t ) noexcept; | (2) | (C++11 起) (C++14 起为 constexpr) |
| template< std::size_t I, class... Types >
typename std::tuple_element<I, tuple<Types...> >::type const& get( const tuple<Types...>& t ) noexcept; | (3) | (C++11 起) (C++14 起为 constexpr) |
| template< std::size_t I, class... Types >
typename std::tuple_element<I, tuple<Types...> >::type const&& get( const tuple<Types...>&& t ) noexcept; | (4) | (C++11 起) (C++14 起为 constexpr) |
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template< class T, class... Types > | (5) | (C++14 起) |
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template< class T, class... Types > | (6) | (C++14 起) |
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template< class T, class... Types > | (7) | (C++14 起) |
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template< class T, class... Types > | (8) | (C++14 起) |
1-4) 从 tuple 提取第 I 个元素。 I 是 [0, sizeof...(Types)) 中的整数值。
5-8) 提取 tuple t 的类型为 T 的元素。若 tuple 不恰好拥有一个该类型元素则编译失败。
参数
| t | - | 要提取内容的 tuple |
返回值
到 t 的被选中元素的引用。
调用示例
#include <tuple>
#include <iostream>
#include <string>
#include <typeinfo>
#include <stdexcept>
#include <iostream>
#include <iterator>
#include <vector>
#include <memory>
#include <set>
#include <map>
struct Cell
{
int x;
int y;
Cell() = default;
Cell(int a, int b): x(a), y(b) {}
Cell(const Cell &cell)
{
x = cell.x;
y = cell.y;
}
Cell &operator+(const Cell &cell)
{
x += cell.x;
y += cell.y;
return *this;
}
Cell &operator+=(const Cell &cell)
{
x += cell.x;
y += cell.y;
return *this;
}
Cell &operator*=(int n)
{
x *= n;
y *= n;
return *this;
}
Cell &operator++()
{
x += 1;
y += 1;
return *this;
}
//std::tie 能用于引入字典序比较到结构体，或解包 tuple ：
bool operator <(const Cell &cell) const
{
return std::tie(x, y) < std::tie(cell.x, cell.y);
}
};
std::ostream &operator<<(std::ostream &os, const Cell &cell)
{
os << "{" << cell.x << "," << cell.y << "}";
return os;
}
// 打印任何大小 tuple 的辅助函数
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<class... Args>
void print(const std::tuple<Args...>& t)
{
std::cout << "(";
TuplePrinter<decltype(t), sizeof...(Args)>::print(t);
std::cout << ")" << std::endl;
}
// 辅助函数结束
int main()
{
//1-4) 从 tuple 提取第 I 个元素。 I 是 [0, sizeof...(Types)) 中的整数值。
std::tuple<int, std::string, float> tuple1(10, "Test", 3.14);
std::cout << "tuple1 " << typeid(tuple1).name() << ": " << std::endl;
print(tuple1);
// 基于下标的访问
std::cout << "std::get<0>(tuple1): " << std::get<0>(tuple1) << std::endl;
std::cout << "std::get<1>(tuple1): " << std::get<1>(tuple1) << std::endl;
std::cout << "std::get<2>(tuple1): " << std::get<2>(tuple1) << std::endl;
std::tuple<Cell, std::string, double> tuple2 = std::make_tuple(Cell{101, 101}, "GGX", 3.14);
std::cout << "tuple2 " << typeid(tuple2).name() << ": " << std::endl;
std::cout << "std::get<0>(tuple2): " << std::get<0>(tuple2) << std::endl;
std::cout << "std::get<1>(tuple2): " << std::get<1>(tuple2) << std::endl;
std::cout << "std::get<2>(tuple2): " << std::get<2>(tuple2) << std::endl;
return 0;
}
输出
tuple1 St5tupleIJiNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEfEE:
(10, Test, 3.14)
std::get<0>(tuple1): 10
std::get<1>(tuple1): Test
std::get<2>(tuple1): 3.14
tuple2 St5tupleIJ4CellNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEdEE:
std::get<0>(tuple2): {101,101}
std::get<1>(tuple2): GGX
std::get<2>(tuple2): 3.14
用 tie 解包 tuple 时用来跳过元素的占位符
std::ignore
|
const /*unspecified*/ ignore; | (C++11 起) (C++17 前) | |
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inline constexpr /*unspecified*/ ignore; | (C++17 起) |
任何值均可赋给而无效果的未指定类型的对象。目的是令 std::tie 在解包 std::tuple 时作为不使用的参数的占位符使用。
调用示例
#include <tuple>
#include <iostream>
#include <string>
#include <typeinfo>
#include <stdexcept>
#include <iostream>
#include <iterator>
#include <vector>
#include <memory>
#include <set>
#include <map>
struct Cell
{
int x;
int y;
Cell() = default;
Cell(int a, int b): x(a), y(b) {}
Cell(const Cell &cell)
{
x = cell.x;
y = cell.y;
}
Cell &operator+(const Cell &cell)
{
x += cell.x;
y += cell.y;
return *this;
}
Cell &operator+=(const Cell &cell)
{
x += cell.x;
y += cell.y;
return *this;
}
Cell &operator*=(int n)
{
x *= n;
y *= n;
return *this;
}
Cell &operator++()
{
x += 1;
y += 1;
return *this;
}
//std::tie 能用于引入字典序比较到结构体，或解包 tuple ：
bool operator <(const Cell &cell) const
{
return std::tie(x, y) < std::tie(cell.x, cell.y);
}
};
std::ostream &operator<<(std::ostream &os, const Cell &cell)
{
os << "{" << cell.x << "," << cell.y << "}";
return os;
}
// 打印任何大小 tuple 的辅助函数
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<class... Args>
void print(const std::tuple<Args...>& t)
{
std::cout << "(";
TuplePrinter<decltype(t), sizeof...(Args)>::print(t);
std::cout << ")" << std::endl;
}
// 辅助函数结束
int main()
{
std::set<Cell> set_of_Cell;
bool inserted = false;
//任何值均可赋给而无效果的未指定类型的对象。
//目的是令 std::tie 在解包 std::tuple 时作为不使用的参数的占位符使用。
std::tie(std::ignore, inserted) = set_of_Cell.insert(Cell{1024, 1024});
if (inserted)
{
std::cout << "Value was inserted successfully" << std::endl;
}
return 0;
}
输出
Value was inserted successfully
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