C++ multi process share value via write and read data from serialized file,the better way is shared_

#include <atomic>
#include <chrono>
#include <cmath>
#include <condition_variable>
#include <cstddef>
#include <forward_list>
#include <fstream>
#include <functional>
#include <future>
#include <iomanip>
#include <iostream>
#include <latch>
#include <list>
#include <map>
#include <memory>
#include <mutex>
#include <optional>
#include <queue>
#include <random>
#include <stack>
#include <string>
#include <thread>
#include <utility>
#include <uuid/uuid.h>
#include <vector>

char *uuid_value = (char *)malloc(40);
char *get_uuid_value()
{
    uuid_t new_uuid;
    uuid_generate(new_uuid);
    uuid_unparse(new_uuid, uuid_value);
    return uuid_value;
}

std::string get_time_now(bool is_exact = true)
{
    std::stringstream ss;
    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);
    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());
        ss << "_" << std::setw(3) << std::setfill('0') << (mills.count() - seconds.count() * 1000)
           << std::setw(3) << std::setfill('0') << (micros.count() - mills.count() * 1000)
           << std::setw(3) << std::setfill('0') << (nanos.count() - micros.count() * 1000);
    }
    return ss.str();
}

std::mutex _write_mtx;

void write_num(std::uint64_t num, const std::string &file_name = "log.txt")
{
    std::lock_guard<std::mutex> _lock_guard(_write_mtx);
    std::fstream w_file(file_name, std::ios::out);
    w_file << num << std::endl;
    w_file.close();
}

std::uint64_t read_num(const std::string &file_name = "log.txt")
{
    std::lock_guard<std::mutex> _lock_guard(_write_mtx);
    std::uint64_t num = 0;
    std::fstream r_file(file_name, std::ios::in);
    std::string line;
    getline(r_file, line);
    if (line != "")
    {
        num = std::stoll(line);
    }
    return num;
}

void print_num()
{
    static std::uint64_t num = 0;
    while (1)
    {
        num = read_num();
        std::cout << ++num<<",thread id:"<<std::this_thread::get_id()<<","<<get_time_now()<< std::endl;
        write_num(num);
        std::this_thread::sleep_for(std::chrono::seconds(1));
    }
}

int main(int agrs, char **argv)
{
    print_num();
    std::cout << get_time_now() << ",thread id:" << std::this_thread::get_id() << ",finished in " << __FUNCTION__ << std::endl;
}

Compile

g++-12 -std=c++2a -I. *.cpp -o h1 -luuid -lpthread