std::ignore (3) - Linux Manuals

std::ignore: std::ignore

NAME

std::ignore - std::ignore

Synopsis

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.

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 = false;
      std::tie(std::ignore, inserted) = set_of_str.insert("Test");
      if (inserted) {
          std::cout << "Value was inserted successfully\n";
      }
  }

Output:

  Value was inserted successfully