c++ 文件操作的 单例模式 范例

//.h
#include 
#include 
#include 
class File {
  public:
    static File &instance();
    void write(const std::string &str);

  private:
    File();
    ~File();
    File(const File &) = delete;
    File & operator = (const File &) = delete;

  private:
    static File           *file_;
    static std::mutex     mutex_;

  private:
    std::ofstream         out_;
};


//.cc
File*       File::file_ = NULL;
std::mutex  File::mutex_;

File::File() {
  out_.open(stats_log_file_name(), std::ofstream::out | std::ofstream::app);
  if(!out_.is_open()){
    CLS_LOG_ERROR << "Open stats file error, file:", cls::Config::instance().stats_log_file_name();
  }
}

File::~File(){
  if(out_.is_open()){
    out_.close();
  }
}

File &File::instance() {
  if (file_ == NULL) {
    std::lock_guard guard(mutex_);
    if (file_ == NULL) {
      file_ = new File();
    }
  }
  return *file_;
}

void File::write(const std::string &str) {
  out_ << str;
  out_.flush();
}