C++ streambuf用法

class LogStreamBuf : public std::streambuf {
　　public:
　　// REQUIREMENTS: "len" must be >= 2 to account for the ‘\n‘ and ‘\n‘.
　　LogStreamBuf(char *buf, int len) {
　　　　setp(buf, buf + len - 2);
　　}
　　// This effectively ignores overflow.
　　virtual int_type overflow(int_type ch) {
　　　　return ch;
　　}

　　// Legacy public ostrstream method.
　　size_t pcount() const { return pptr() - pbase(); }
　　char* pbase() const { return std::streambuf::pbase(); }
};

class LogStream : public std::ostream {
   public:
    　　LogStream(char *buf, int len, int ctr)
        　　: std::ostream(NULL),
          　　streambuf_(buf, len),
          　　ctr_(ctr),
          　　self_(this) { rdbuf(&streambuf_);}

    　　int ctr() const { return ctr_; }
    　　void set_ctr(int ctr) { ctr_ = ctr; }
    　　LogStream* self() const { return self_; }

    　　// Legacy std::streambuf methods.
    　　size_t pcount() const { return streambuf_.pcount(); }
   　　 char* pbase() const { return streambuf_.pbase(); }
   　　 char* str() const { return pbase(); }

  private:
   　　 base_logging::LogStreamBuf streambuf_;
    　　int ctr_;  // Counter hack (for the LOG_EVERY_X() macro)
    　　LogStream *self_;  // Consistency check hack
  };