How can ignore some elements of tuple?

Question

I have a tuple with some elements, and I want to assign some elements of tuple to variables, and ignore some of them.

 auto tuple1 = std::make_tuple(1,2,3,4);
 // variable a should be placeholder 1 in tuple and variable b should be place holder 3;
 int a,b ;

score 4 · Accepted Answer · answered Jul 23 '20 at 20:11

4

You could use from std::tie and std::ignore in tuple such as :

 int a, b;
 tie(std::ignore, a, std::ignore, b)= tuple1;

answered Jul 23 '20 at 20:11

Farhad Sarvari

score 1 · Answer 2 · answered Jul 23 '20 at 21:39

If you use the strutural binding along with C++20 support, you could write

#include <tuple>    

auto tuple1 = std::make_tuple(1, 2, 3, 4);
[[maybe_unused]] auto [dummy1, a, dummy2, b] = tuple1;

Use only a and b. The [[maybe_unused]] part is to suppres the warning due to -Wunused-variable.

This is actually inspired from the answer: structured binding with [[maybe_unused]]

2 Answers2