Lecture 6: Input/Output (II)

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Lecture 6 Input/Output (II)

• Introduction to Computer Science
• Spring 2006

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Contents

• Write data to the standard output device
• Use manipulators in a program to format output
• Perform input and output operations with the
  string data type
• File input and output

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Writing to Standard Output

• Syntax of cout when used with ltlt
• coutltltexpression or manipulator
• ltltexpression or manipulator...
• Expression is evaluated
• Value is printed
• Manipulator is used to format the output

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Formatting Output

• endl manipulator moves output to the beginning of
  the next line
• setprecision(n) outputs decimal numbers with up
  to n decimal places
• fixed outputs floating-point numbers in a fixed
  decimal format
• showpoint forces output to show the decimal point
  and trailing zeros

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The setw Manipulator

• setw outputs the value of an expression in
  specific columns
• If the number of columns exceeds the number of
  columns required by the expression
• Output of the expression is right-justified
• Unused columns to the left are filled with spaces

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The flush Function

• flush clears the buffer, even if it is not full
• Unlike endl, it does not move the cursor to the
  beginning of the next line
• The syntax for flush
• ostreamVar.flush()
• ostreamVar is an output stream variable
• flush can be used as a manipulator
• coutltltflush

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Additional Output Formatting Tools

• Output stream variables can use setfill to fill
  unused columns with a character
• left left-justifies the output
• ostreamVarltltleft
• Disable left by using unsetf
• right right-justifies the output
• ostreamVar ltlt right

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Types of Manipulators

• Two types of manipulators
• With parameters
• Without parameters
• Parameterized require iomanip header
• setprecision, setw, and setfill
• Nonparameterized require iostream header
• endl, fixed, showpoint, left, and flush

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I/O and the string Type

• An input stream variable (cin) and extraction
  operator gtgt can read a string into a variable of
  the data type string
• Extraction operator
• Skips any leading whitespace characters and
  reading stops at a whitespace character
• Should not be used to read strings with blanks
• The function getline
• Reads until end of the current line
• Should be used to read strings with blanks

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File Input/Output

• File area in secondary storage to hold info
• File I/O
• Include fstream header
• Declare file stream variables
• Associate the file stream variables with the
  input/output sources
• Use the file stream variables with gtgt, ltlt, or
  other input/output functions
• Close the filesFile Input/Output

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End of lecture 6

• Thank you!