std::ignore - cppreference.com

##### cppreference.com

##### Search

Create account

##### Namespaces

- Page
- Discussion

##### Variants

##### Views

- View
- Edit
- History

##### Actions

# std::ignore

From cppreference.com
< cpp‎ | utility‎ | tuple

Defined in header `<tuple>` |  |
const /*unspecified*/ ignore; |  | (since C++11)

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 sucessfully\n";
        }
    }

Output:

    Value was inserted sucessfully

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

Retrieved from "http://en.cppreference.com/mwiki/index.php?title=cpp/utility/tuple/ignore&oldid=63117"