bench-fmtlib.cpp

// Written with ChatGPT
#include <iostream>
#include <chrono>
#include <format>
#include <print>
#include <fmt/core.h>
#include <fmt/format.h>
#include <fmt/chrono.h>
#include <fmt/ranges.h>

constexpr int ITERATIONS = 1'000'000;

template <typename Func>
auto benchmark(Func&& func, const std::string& name) {
    auto start = std::chrono::high_resolution_clock::now();
    func();
    auto end = std::chrono::high_resolution_clock::now();
    std::chrono::duration<double, std::milli> duration = end - start;
    std::cout << name << ": " << duration.count() << " ms\n";
}

int main() {
    std::string result;

    benchmark([] {
        for (int i = 0; i < ITERATIONS; ++i) {
            std::format("Hello, {}! The answer is {}.", "world", 42);
        }
    }, "std::format");

    benchmark([] {
        for (int i = 0; i < ITERATIONS; ++i) {
            fmt::format("Hello, {}! The answer is {}.", "world", 42);
        }
    }, "fmt::format");

    benchmark([&result] {
        for (int i = 0; i < ITERATIONS; ++i) {
            result = std::format("Hello, {}! The answer is {}.", "world", 42);
        }
    }, "std::format (with assignment)");

    benchmark([&result] {
        for (int i = 0; i < ITERATIONS; ++i) {
            result = fmt::format("Hello, {}! The answer is {}.", "world", 42);
        }
    }, "fmt::format (with assignment)");

    /* benchmark([] { */
    /*     for (int i = 0; i < ITERATIONS; ++i) { */
    /*         std::print("Hello, {}! The answer is {}.\n", "world", 42); */
    /*     } */
    /* }, "std::print"); */

    /* benchmark([] { */
    /*     for (int i = 0; i < ITERATIONS; ++i) { */
    /*         fmt::print("Hello, {}! The answer is {}.\n", "world", 42); */
    /*     } */
    /* }, "fmt::print"); */

    return 0;
}

std::format: 76.9111 ms
fmt::format: 50.1275 ms
std::format (with assignment): 60.5027 ms
fmt::format (with assignment): 51.9799 ms

Results looks odd, why does with assigment works faster