< cpp‎ | utility‎ | tuple
Defined in header <tuple>
template< class... Types >
tuple<Types&...> tie( Types&... args ) noexcept;
(since C++11)
(constexpr since C++14)

Creates a tuple of lvalue references to its arguments or instances of std::ignore.


args - zero or more lvalue arguments to construct the tuple from

Return value

A std::tuple object containing lvalue references.

Possible implementation

namespace detail {
struct ignore_t {
    template <typename T>
    const ignore_t& operator=(const T&) const { return *this; }
const detail::ignore_t ignore;
template <typename... Args>
auto tie(Args&... args) {
    return std::tuple<Args&...>(args...);


std::tie may be used to unpack a std::pair because std::tuple has a converting assignment from pairs:

bool result;
std::tie(std::ignore, result) = set.insert(value);


std::tie can be used to introduce lexicographical comparison to a struct or to unpack a tuple:

#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";


Value was inserted successfully

See also

creates a tuple object of the type defined by the argument types
(function template)
creates a tuple of rvalue references
(function template)
creates a tuple by concatenating any number of tuples
(function template)
placeholder to skip an element when unpacking a tuple using tie