std::tie
Defined in header <tuple> | ? | ? |
|---|---|---|
template< class... Types > tuple<Types&...> tie( Types&... args ); | ? | (since C++11) (until C++14) |
template< class... Types > constexpr tuple<Types&...> tie( Types&... args ); | ? | (since C++14) |
创建对其参数或实例的lvalue引用的元组。std::ignore...
参数
args | - | zero or more lvalue arguments to construct the tuple from |
|---|
返回值
阿std::tuple对象，其中包含lvalue引用。
例外
noexcept规格：
noexcept
注记
std::tie可用于解压std::pair因为std::tuple有一个转换分配成对：
二次
bool result;
std::tie(std::ignore, result) = set.insert(value);二次
例
std::tie可用于将词典编纂比较引入到结构中，或用于解压元组：
二次
#include <iostream>
#include <string>
#include <set>
#include <tuple>
struct S {
int n;
std::string s;
float d;
bool operator<(const S& rhs) const
{
// compares n to rhs.n,
// then s to rhs.s,
// then d to rhs.d
return std::tie(n, s, d) < std::tie(rhs.n, rhs.s, rhs.d);
}
};
int main()
{
std::set<S> set_of_s; // S is LessThanComparable
S value{42, "Test", 3.14};
std::set<S>::iterator iter;
bool inserted;
// unpacks the return value of insert into iter and inserted
std::tie(iter, inserted) = set_of_s.insert(value);
if (inserted)
std::cout << "Value was inserted successfully\n";
}二次
产出：
二次
Value was inserted successfully二次
make_tuple | creates a tuple object of the type defined by the argument types (function template) |
|---|---|
forward_as_tuple | creates a tuple of rvalue references (function template) |
tuple_cat | creates a tuple by concatenating any number of tuples (function template) |
ignore | placeholder to skip an element when unpacking a tuple using tie (constant) |
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