std::piecewise_construct_t
来自cppreference.com
| 定义于头文件 <utility>
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| struct piecewise_construct_t { }; |
(C++11 起) (C++17 前) |
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| struct piecewise_construct_t { explicit piecewise_construct_t() = default; }; |
(C++17 起) | |
std::piecewise_construct_t 是用于在接收二个 tuple 参数的不同函数间消歧义的空结构体标签类型。
不使用 std::piecewise_construct_t 的重载假设每个 tuple 参数各变成一个 pair 的元素。使用 std::piecewise_construct_t 的重载假设每个 tuple 参数用于逐块构造一个指定类型的新对象，而它将成为 pair 的元素。
示例
运行此代码
#include <iostream> #include <utility> #include <tuple> struct Foo { Foo(std::tuple<int, float>) { std::cout << "Constructed a Foo from a tuple\n"; } Foo(int, float) { std::cout << "Constructed a Foo from an int and a float\n"; } }; int main() { std::tuple<int, float> t(1, 3.14); std::pair<Foo, Foo> p1(t, t); std::pair<Foo, Foo> p2(std::piecewise_construct, t, t); }
输出：
Constructed a Foo from a tuple Constructed a Foo from a tuple Constructed a Foo from an int and a float Constructed a Foo from an int and a float
参阅
| (C++11) |
用于为逐段构造的函数消歧义的 piecewise_construct_t 类型的对象 (常量) |
| 构造新的 pair ( std::pair<T1,T2> 的公开成员函数)
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