Streams

1

• Streams

One of the themes of this course is that
everything can be reduced to simple (and
similiar) concepts. Streams are one example.
Keyboard and Screen are the standard I/O
devices. Later, when we need to add file I/O, we
will see that files are also streams. Everything
we just learned will be the same for files as it
was for standard I/O.
2

• C Stream I/O

• C introduces the concept of a stream as the
  input/output object. (Java also uses the stream
  concept)
• A stream contains characters coming from some
  input device
• Or a stream contains characters going to some
  output device

3

• C Stream I/O (cont)

• To use standard stream I/O, we include the header
  file iostream.h in our program
• To use file I/O, we include the header file
  fstream.h in our program.

include ltiostream.hgt include ltfstream.hgt

• To use a character array as a stream, we include
  the header file strstrea.h in our program.

4

• Input and Output (Standard)

• Input uses an istream
• Output uses an ostream
• cin is associated with the standard input device,
  i.e. the keyboard
• cout is associated with the standard output
  device, i.e. the monitor screen

5

• Input and Output ( files )

include ltfstream.hgt ifstream inData ofstream
outData

• Input uses an ifstream
• Output uses an ofstream
• inData is then associated with the input file
• outData is associated with the the output file

6

• Extraction and Insertion

• To get characters from the input stream, we use
  the extraction operator gtgt.
• To put characters on the output stream, we use
  the insertion operator ltlt.
• The direction the operator points, makes it easy
  to remember which is which.

7

• Extraction and Insertion (cont)

• cin gtgt someInt means extract (get) some integer
  from the input stream.
• cout ltlt someInt means insert (put) some integer
  on the output stream

8

• Streams

• Streams convert characters into values of
  appropriate data types.
• cin gtgt someInt looks for a sequence of characters
  which represents an integer.
• cout ltlt "The answer is " ltlt someInt first outputs
  a string and then outputs the characters
  representing the value of someInt.

9

• Streams (cont)

• cin and cout operate on character, or text
  streams.
• Text streams have the concept of lines and '\n'
  is the newline character.
• cout ltlt someInt ltlt '\n'

10

• Streams (cont)

• endl is a better way to represent the newline
  character since it is more in keeping with the
  concepts of abstraction.
• cout ltlt someInt ltlt endl

11

• get and getline

• Sometimes we want more control over the input or
  output stream.
• cin.get(ch) will get a single character.
• cin.getline(str,81) will get an entire line (up
  to 80 characters) and will consume the newline
  character.
• cin.ignore(80, '\n') skips 80 characters
• or skip to the start of the next line.

12

• put and putback

• cout.put(ch) outputs a single character.
• cin.putback(ch) returns a character to the input
  stream.

13

• Testing the state of a stream

• When processsing characters from the input
  stream, we often need to know when the stream is
  empty of characters.
• The stream returns a value for the success or
  failure of the last operation.

cin gtgt someInt // the priming
read while (cin) // the test for success
process(someInt) // do loop if true
cin gtgt someInt // the looping
read