Streams and Files Version

1
Streams and Files Version 2

• Streams are packets of characters
• (or other objects)
• Smalltalk uses streams in
• files and
• in windows

2
Streams

• File Methods
• input output explanation
• next nextPut single character
• nextChunk show multiple characters
• (strings)
• upTo
  inputs field up to a
• 
  a specific character
• close close must use for files
• atEnd required for input files

3
CLASS HIERARCY

• Hierarchy of STREAM classes
• Object
• Stream
• Read Stream
• WriteStream
• Hierarchy of FILE classes
• Object
• CfsFileStream
• CfsReadFileStream
• CfsWriteFileStream

4
Streams

• Defining a File to write to
• Use class method called open or openEmpty
• For example
• cityFile CfsWriteFileStream
  open'a\file.txt.
• open message assumes that no file with the name
  already exists
• Use class method openEmpty to open an existing
  file with the same name
• note existing file with the same name will be
  erased

5
Streams

• Copying a DOS file
• fileIn fileOut char
• fileIn CfsReadFileStream open
  'c\cis234\cities.txt'.
• fileOut CfsWriteFileStream open
  c\cis234\citout.txt'.
• fileIn atEnd
• whileFalse char fileIn next.
• fileOut nextPut char.
• fileIn close.
• fileOut close

6
Copying a DOS file to the window

• window char file
• window EtWorkspace new.
• window label 'File Window'.
• window open.
• file CfsReadFileStream open
  'c\cis234\citout.txt'.
• file atEnd
• whileFalse char file next.
• window nextPut char.
• file close

7
A DOS file with comma delimited fields can be
read as follows

• cityFile CfsReadFileStream open
  a\city.txt.
• cityFile atEnd
• whileFalse
• zipCode cityFile upTo ,.
• stateName cityFile upTo ,.
• city cityFile upTo cr.
• cityFile upTo lf.
• Transcript show (zipCode , , city).
• inFile close.

8
Streams

• The cr and lf stand for carriage return and line
  feed
• These two characters exist at the end of each
  ASCII record
• To obtain the values for these two characters use
  the following conversions
• lf 10 asCharacter
• cr 13 asCharacter

9
Streams

• There is a need for permanent storage of any
  Smalltalk object.
• There are two ways to do this
• 1. ASCII form .sto (stored objects)
• 2. Binary form .obj (filed objects)
• For a beginning student the ASCII form is
  desirable

10
Streams

• Thus it is possible to store and restore object
  contents easily
• This facilitates transporting objects between
  computer systems

11
Streams

• Any object can be quickly stored in ASCII format
  on disk using
• array (Honda Toyota Saturn).
• arrayFile CfsWriteFileStream
  openEmpty 'c\array.sto'.
• array storeOn arrayFile.
• arrayFile close.

12
Streams

• Any object can be quickly restored on disk using
• array nil.
• arrayFile CfsReadFileStream open
  'c\array.sto'.
• array Compiler evaluate
• arrayFile contents.
• arrayFile close.
• array inspect.

13
Streams

• Summary
• Smalltalk Programmers can store objects to files
  to save their contents for later use
• ASCII files are mainly used to communicate to
  other applications