在C ++中，系统如何实现缓冲流？

Question

有人可以编写一些示例代码来解释这个概念吗？我知道使用缓冲流的目的，但我也想知道如何实施。

提前致谢！

Answer 1

您可以查看平台的实现，C ++标准或 Angelika Langer和Klaus Kreft的“标准C ++ iostreams and Locales”.

为学习曲线做好准备。溪流很古老，而且很复杂。 （弗朗西斯·格拉斯伯洛（Francis Glassborow）： “我很少疑问我/O库是任何语言中最困难的方面之一。”)

Answer 2

Veeeery在示意性上，用于“输入”流：

class BufferedInputStream
{
public:
  BufferedInputStream(SomeExternalDevice d)
  : m_Device(d),
    m_Current(m_Buffer),
    m_End(m_Buffer)
  {}

  char get(){
    if (!IsDataAvailableInBuffer()){
      ReadAChunkFromDiskAndPutItInBuffer();
    }
    return PopByteFromBuffer();
  }

private:

  bool IsDataAvailableInBuffer()const{
    return m_Current != m_End;
  }

  void ReadAChunkFromDiskAndPutItInBuffer(){
    // Buffer must be empty
    assert(!IsDataAvailableInBuffer());

    // Read bytes from the device
    bytes_read = Read(m_Device, m_Buffer, BufferSize);

    // Reposition the "begin" and "end" pointers
    m_Current = m_Buffer;
    m_End = m_Buffer + bytes_read;
  }

  char PopByteFromBuffer(){
    assert(IsDataAvailableInBuffer());
    return *m_Current++;
  }

  // For example, an OS file handle
  SomeExternalDevice m_Device;

  // The buffer itself
  char m_Buffer[BufferSize];

  // Begin of buffer contents
  char* m_Current;

  // End of buffer contents
  char* m_End;
};

这样，从磁盘读取数据的数据是缓冲区大小的块，并且大多数调用“ get（）”的调用不必最终呼叫到OS，因为它们可以简单地从缓冲区返回字节。

Answer 3

看一下STL实现sstream和sstream.tcc （链接到SGI STL实现）。

基地 stringstream 班级是 basic_stringstream, ，实现 basic_iostream 界面。

  // [27.7.4] Template class basic_stringstream
  /**
   *  @brief  Controlling input and output for std::string.
   *
   *  This class supports reading from and writing to objects of type
   *  std::basic_string, using the inherited functions from
   *  std::basic_iostream.  To control the associated sequence, an instance
   *  of std::basic_stringbuf is used, which this page refers to as @c sb.
  */

有基类 basic_stringbuf 来自 basic_streambuf. 。这可以容纳缓冲区。

  // [27.7.1] template class basic_stringbuf
  /**
   *  @brief  The actual work of input and output (for std::string).
   *
   *  This class associates either or both of its input and output sequences
   *  with a sequence of characters, which can be initialized from, or made
   *  available as, a @c std::basic_string.  (Paraphrased from [27.7.1]/1.)
   *
   *  For this class, open modes (of type @c ios_base::openmode) have
   *  @c in set if the input sequence can be read, and @c out set if the
   *  output sequence can be written.
  */