Kate Gregory with material from Deitel and Deitel

1
Week 9

• Midterm is marked
• Lab 4 is not marked
• Lab 5 is due now
• Stream IO
• Lab 6

2
Midterm

• Average 36.4/50 73
• High mark 49/50
• Each and every question earned somebody full
  marks
• Section 2 was the hardest
• Be sure to follow instructions
• Take by reference, write a constructor, etc

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Stream IO

• Simple input and output is easy to do
• cout ltlt Enter a number
• cin gtgt x
• Type aware
• Allows tremendous power through operator
  overloading
• cout ltlt NewHire

5
What was wrong with printf?

• You had to tell it the types involved
• printf(x is d, x)
• If you lied to it, very strange things happened
• Tremendous vulnerability for things like buffer
  overflow attacks when reading a string
• There was no simple way to print a struct, array,
  or other non-built-in type

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What was good about printf?

• The f is for formatted
• Easy to set precision and padding
• printf(5.2f,x)
• Terrific for tables and reports
• So how do we achieve this with cin and cout?

7
C Stream IO

• cin is an instance of the istream class
• cout is an instance of the ostream class, as is
  cerr
• The gtgt and ltlt operators can be overloaded to
  teach the istream and ostream classes how to
  handle your classes

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Manipulators

• Manipulators change the behaviour of the stream
  when they are sent to it
• cout ltlt "hello" ltlt endl
• cout ltlt x ltlt flush
• Standard manipulators are defined in iomanip or
  iomanip.h
• You can even write your own manipulators

9
Setting the base

• int x 32
• cout ltlt x ltlt in hex is
• cout ltlt hex ltlt x ltlt dec
• hex for hexadecimal
• dec for decimal (ordinary)
• oct for octal
• setbase(n) to specify numerically

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Setting the precision

• setprecision manipulator
• float f 1.23456
• cout ltlt f ltlt endl
• cout ltlt setprecision(2)
• cout ltlt f ltlt endl
• cout ltlt setprecision(0)

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Setting the Width

• setw manipulator
• int i1
• int j12
• int k123
• cout ltlt setw(5)
• cout ltlt i ltlt endl
• cout ltlt setw(5)
• cout ltlt j ltlt endl
• cout ltlt setw(5)
• cout ltlt k ltlt endl

12
Member Functions

• cin and cout are objects. They have member
  functions as any other object does.
• cout.precision() is the same as the setprecision
  manipulator
• cout.width() is the same as the setw manipulator
• cin.getline()reads an entire line, spaces and
  all, into a string

13
Setting the Justification

• Another manipulator sets a number of internal
  flags to cover things like alignment
• cout ltlt setw(5) ltlt i ltlt endl
• cout ltlt setw(5) ltlt setiosflags(iosleft) ltlt i ltlt
  endl
• cout ltlt setiosflags(iosright)
• Default is right-aligned within the width

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Setting the Fill Character

• cout.fill('')
• cout ltlt setw(5) ltlt j ltlt endl
• cout.fill(' ')
• cout ltlt setw(5) ltlt j ltlt endl
• Note single quotes
• Default is space

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You have tremendous control

• Check the text or your online documentation for
  other manipulators, member functions, and flags
• Remember you can use all this power when printing
  integers and floats, as here, but also in your
  own classes when overloading ltlt and gtgt

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For Next class

• Read chapters 12 and 13
• Lab 6