详解C++编程中的静态成员与可变数据成员

// static_data_members.cpp
class BufferedOutput
{
public:
  // Return number of bytes written by any object of this class.
  short BytesWritten()
  {
   return bytecount;
  }

  // Reset the counter.
  static void ResetCount()
  {
   bytecount = 0;
  }

  // Static member declaration.
  static long bytecount;
};

// Define bytecount in file scope.
long BufferedOutput::bytecount;

int main()
{
}

long nBytes = BufferedOutput::bytecount;

BufferedOutput Console;

long nBytes = Console.bytecount;

mutable member-variable-declaration;

// mutable.cpp
class X
{
public:
  bool GetFlag() const
  {
   m_accessCount++;
   return m_flag;
  }
private:
  bool m_flag;
  mutable int m_accessCount;
};

int main()
{
}