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#### 21.1.1 Introduction to Streams

A stream is an object that can be used with an input or output function to identify an appropriate source or sink of characters or bytes for that operation. A character stream is a source or sink of characters. A binary stream is a source or sink of bytes.

Some operations may be performed on any kind of stream; Figure 21–1 provides a list of standardized operations that are potentially useful with any kind of stream.

      close                 stream-element-type
      input-stream-p        streamp
      interactive-stream-p  with-open-stream
      output-stream-p

      Figure 21–1: Some General-Purpose Stream Operations

Other operations are only meaningful on certain stream types. For example, read-char is only defined for character streams and read-byte is only defined for binary streams.