The binding that copied

#include <iostream>
#include <utility>

int main() {
    auto p = std::make_pair(1, 2);
    auto [a, b] = p;
    ++a;
    std::cout << "a=" << a << " p.first=" << p.first << '\n';
}

Plain auto structured bindings copy each element. ++a changes the copy, not the pair.

Observed output: a=2 p.first=1.

Fix: auto& [a, b] = p; to bind references.

Lesson: a structured binding follows the same copy-vs-reference rule as any other auto declaration.

Facts verified 2026-11-04. The code on this page was compiled and run on the box with GCC 16.2.0 at -std=c++23 -Wall -Wextra; the outputs quoted are the observed outputs. MSVC was not tested.

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