A sorted map backed by vectors (std::flat_map, C++23)

std::flat_map keeps keys sorted like a map but stores them in vectors, so iteration is cache-friendly and there is no per-node allocation.

#include <flat_map>
#include <iostream>
#include <string>

int main() {
    // Sorted associative container backed by vectors, not a node tree.
    std::flat_map<std::string, int> scores;
    scores["ada"] = 95;
    scores["grace"] = 88;
    scores["ada"] += 5;
    for (auto [name, score] : scores) {
        std::cout << name << ": " << score << '\n';
    }
    std::cout << "size=" << scores.size() << '\n';
}

Observed output:

ada: 100
grace: 88
size=2

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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