Function write

dds/DCPS/MessageBlock.h:50–50

  char* wr_ptr() const { return base() + wr_ptr_; }
  void write(size_t diff) { wr_ptr_ += diff; }
  void unwrite(size_t diff) { wr_ptr_ -= diff; }

  size_t len() const { return wr_ptr_ - rd_ptr_; }