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| Member functions | ||||
| Non-member functions | ||||
tie | ||||
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20) | ||||
| Helper concepts | ||||
(C++23) | ||||
| Helper classes | ||||
(C++23) | ||||
(C++23) | ||||
| Deduction guides(C++17) |
Defined in header <tuple> | ||
template<class...Types> std::tuple<Types&...> tie( Types&...args)noexcept; | (since C++11) (constexpr since C++14) | |
Creates a tuple of lvalue references to its arguments or instances ofstd::ignore.
Contents |
| args | - | zero or more lvalue arguments to construct the tuple from. |
Astd::tuple object containing lvalue references.
template<typename...Args>constexpr// since C++14std::tuple<Args&...> tie(Args&...args)noexcept{return{args...};} |
std::tie may be used to unpack astd::pair becausestd::tuple has aconverting assignment from pairs:
bool result;std::tie(std::ignore, result)= set.insert(value);
1)std::tie can be used to introduce lexicographical comparison to a struct or to unpack a tuple;
2)std::tie can work withstructured bindings:
#include <cassert>#include <iostream>#include <set>#include <string>#include <tuple> struct S{int n;std::string s;float d; friendbool operator<(const S& lhs,const S& rhs)noexcept{// compares lhs.n to rhs.n,// then lhs.s to rhs.s,// then lhs.d to rhs.d// in that order, first non-equal result is returned// or false if all elements are equalreturn std::tie(lhs.n, lhs.s, lhs.d)< std::tie(rhs.n, rhs.s, rhs.d);}}; int main(){// Lexicographical comparison demo:std::set<S> set_of_s; S value{42,"Test",3.14};std::set<S>::iterator iter;bool is_inserted; // Unpack a pair: std::tie(iter, is_inserted)= set_of_s.insert(value);assert(is_inserted); // std::tie and structured bindings:auto position=[](int w){returnstd::tuple(1* w,2* w);}; auto[x, y]= position(1);assert(x==1&& y==2); std::tie(x, y)= position(2);// reuse x, y with tieassert(x==2&& y==4); // Implicit conversions are permitted:std::tuple<char,short> coordinates(6,9); std::tie(x, y)= coordinates;assert(x==6&& y==9); // Skip an element:std::string z; std::tie(x,std::ignore, z)=std::tuple(1,2.0,"Test");assert(x==1&& z=="Test");}
| Structured binding(C++17) | binds the specified names to sub-objects or tuple elements of the initializer[edit] |
(C++11) | creates atuple object of the type defined by the argument types(function template)[edit] |
(C++11) | creates atuple offorwarding references(function template)[edit] |
(C++11) | creates atuple by concatenating any number of tuples(function template)[edit] |
(C++11) | placeholder to skip an element when unpacking atuple usingtie(constant)[edit] |
