c++ linux download file via libcurl

sudo apt install curl

 #include <chrono> 
#include <ctime>
#include <curl/curl.h>
#include <curl/easy.h> 
#include <iostream> 
#include <iomanip>
#include <stdio.h>  

std::string get_time_now(bool is_exact = false)
{
    std::chrono::time_point<std::chrono::high_resolution_clock> now = std::chrono::high_resolution_clock::now();
    time_t raw_time = std::chrono::high_resolution_clock::to_time_t(now);
    struct tm tm_info = *localtime(&raw_time);
    std::stringstream ss;
    ss << std::put_time(&tm_info, "%Y%m%d%H%M%S");
    if (is_exact)
    {
        std::chrono::seconds seconds = std::chrono::duration_cast<std::chrono::seconds>(now.time_since_epoch());
        std::chrono::milliseconds mills = std::chrono::duration_cast<std::chrono::milliseconds>(now.time_since_epoch());
        std::chrono::microseconds micros = std::chrono::duration_cast<std::chrono::microseconds>(now.time_since_epoch());
        std::chrono::nanoseconds nanos = std::chrono::duration_cast<std::chrono::nanoseconds>(now.time_since_epoch());
        std::uint64_t mills_count = mills.count() - seconds.count() * 1000;
        std::uint64_t micros_count = micros.count() - mills.count() * 1000;
        std::uint64_t nanos_count = nanos.count() - micros.count() * 1000;
        ss << "-" << std::setw(3) << std::setfill('0') << std::to_string(mills_count)
           << std::setw(3) << std::setfill('0') << std::to_string(micros_count)
           << std::setw(3) << std::setfill('0') << std::to_string(nanos_count);
    }

    return ss.str();
}
 
size_t write_data(void *ptr, size_t size, size_t nmemb, FILE *stream)
{
    size_t written = fwrite(ptr, size, nmemb, stream);
    return written;
}

void download_file()
{
    std::cout<<get_time_now(true)<<",start in "<<__FUNCTION__<<std::endl;
    CURL *curl;
    FILE *fp;
    CURLcode res;
    char *url = "https://www.mica.edu.vn/perso/Vu-Hai/EE3490/Ref/The%20C++Standard%20Library%20-%202nd%20Edition.pdf";
    char outfilename[FILENAME_MAX] = "/home/fred/C/aaaaa.pdf";
    curl = curl_easy_init();
    if (curl)
    {
        fp = fopen(outfilename, "wb");
        curl_easy_setopt(curl, CURLOPT_URL, url);
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
        res = curl_easy_perform(curl);
        /* always cleanup */
        curl_easy_cleanup(curl);
        fclose(fp);
    }
    std::cout<<get_time_now(true)<<",finish in "<<__FUNCTION__<<std::endl;
}

int main(void)
{
    download_file();
    return 0;
}

g++ -std=c++2a -I. *.cpp -o h1 -luuid -lpthread -lcurl

./h1