把ms的时间戳转换成格式化输出到ms的字符串

static std::string get_format_time(int64_t ms) {
    int microsec = ms%1000;

    time_t t(ms / 1000);
    struct tm *p = localtime(&t);
    char s[100];
    int pos = strftime(s, sizeof(s), "%Y%m%d-%H:%M:%S", p);

    sprintf(&s[pos], ".%03d", microsec);

    return std::string(s);
}

int main()
{
    std::cout << get_format_time(1604992150091) << std::endl;

    return 0;
    
}