Defined in header <tuple>
const /*unspecified*/ ignore;
(since C++11)
(until C++17)
inline constexpr /*unspecified*/ ignore;
(since C++17)

An object of unspecified type such that any value can be assigned to it with no effect. Intended for use with std::tie when unpacking a std::tuple, as a placeholder for the arguments that are not used.

While the behavior of std::ignore outside of std::tie is not formally specified, some code guides recommend using std::ignore to avoid warnings from unused return values of [[nodiscard]] functions.

Possible implementation

namespace detail {
struct ignore_t
    template <typename T>
    constexpr // required since C++14
    void operator=(T&&) const noexcept {}
inline constexpr detail::ignore_t ignore; // 'const' only until C++17


  1. Demonstrates the use of std::ignore together with a [[nodiscard]] function.
  2. Unpacks a std::pair<iterator, bool> returned by std::set::insert(), but only saves the boolean.
#include <iostream>
#include <set>
#include <string>
#include <tuple>
[[nodiscard]] int dontIgnoreMe()
    return 42;
int main()
    std::ignore = dontIgnoreMe();
    std::set<std::string> set_of_str;
    bool inserted = false;
    std::tie(std::ignore, inserted) = set_of_str.insert("Test");
    if (inserted)
        std::cout << "Value was inserted successfully\n";


Value was inserted successfully

See also

creates a tuple of lvalue references or unpacks a tuple into individual objects
(function template)

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