Chapter 11-2 Operator Overloading

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Chapter 11-2Operator Overloading

• C, How to Program
• Deitel Deitel

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Streams

• C I/O occurs in streams sequences of bytes
• Input
• Bytes flow from a device to main memory
• Output
• Bytes flow from main memory to a device
• I/O transfers typically take longer than
  processing the data

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Standard Streams

• C standard stream libraries
• Enables I/O operations with Unicode characters
• Unicode character set
• Represents most of the worlds commercially
  viable languages, mathematical symbols and more
• www.unicode.org

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ltiostreamgt header file

• Declares basic services required for all
  stream-I/O operations
• Defines input/output classes
• istream
• ostream
• Defines standard stream objects
• cin the standard input stream object
• cout the standard output stream object

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Stream operators overloading

• Stream insertion operator
• Left-shift operator (ltlt) is overloaded for stream
  output
• Left operand of type ostream
• Such as cout object in cout ltlt classObject
• Stream extraction operator
• Right-shift operator(gtgt) is overloaded for stream
  input
• Left operand of istream
• Such as cin object in cin gtgt classObject
• Already overloaded to process each built-in type
• Thus, both must be global functions

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friend function

• Use global function with two arguments
• One argument must be class object or reference
• Often use friend function for performance reason.
• friend function of a class is defined outside
  that classs scope (external function), yet has
  the right to access the non-public and public
  members of the class.
• We declare a prototype of this external function
  within the class with keyword friend.

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operatorgtgt

• friend function (global function)
• //Complex.h
• friend istream operatorgtgt( istream , Complex
  ) //(real,img)
• //Complex.cpp
• istream operatorgtgt(istream input, Complex
  cNumber)
• double real, imaginary
• input.ignore(256, '(') //ignor (
• input gtgt real //read real part
• input.ignore(256,',') //white spaces up to
  next "," are ignored.
• input gtgt imaginary //read imaginary part
• input.ignore(256,')') //ignore white spaces
  after it.
• if (input.good())
• cNumber.real real
• cNumber.imaginary imaginary
• return input // enable cin gtgt c1 gtgt c2 gtgt c3

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Operatorltlt

• friend function (global function)
• //Complex.h
• friend ostream operatorltlt(ostream , const
  Complex )
• //(real,imaginary)
• //Complex.cpp
• ostream operatorltlt(ostream output,
• const Complex
  cNumber)
• output ltlt "(" ltlt cNumber.real
• ltlt", ltlt cNumber.imaginary ltlt ")"
• return output //enable cout ltlt c1 ltlt c2 ltlt
  c3

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Restrictions on Operator Overloading

• Cannot change
• Precedence of operator (order of evaluation)
• Use parentheses to force order of operators
• Associativity (left-to-right or right-to-left)
• Number of operands
• e.g., is unary, can only act on one operand
• How operators act on built-in data types (i.e.,
  cannot change integer addition)

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Restrictions on Operator Overloading

• Cannot create new operators
• Operators must be overloaded explicitly
• Overloading and does not overload
• Operator ? cannot be overloaded

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Fig. 11.1 Operators that can be overloaded.
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Fig. 11.2 Operators that cannot be overloaded.
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Restrictions on Operator Overloading

• At least one argument of an operator function
  must be an object or reference of a user-defined
  type. This prevents programmers from changing how
  operators work on fundamental types.

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Reference

• Reproduced from the Cyber Classroom for C, How
  to Program, 5/e by Deitel Deitel.
• Reproduced by permission of Pearson Education,
  Inc.