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# std::ignore

From cppreference.com
< cpp‎ | utility‎ | tuple

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.

### [edit] Example

unpack a pair returned by set.insert(), but only save the boolean.

Run this code

    #include <iostream>
    #include <string>
    #include <set>
    #include <tuple>

    int main()
    {
        std::set<std::string> set_of_str;
        bool inserted;
        std::tie(std::ignore, inserted) = set_of_str.insert("Test");
        if (inserted) {
            std::cout << "Value was inserted successfully\n";
        }
    }

Output:

    Value was inserted successfully

tie | creates a `tuple` of lvalue references or unpacks a tuple into individual objects (function template) [edit]

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