Type Conversions

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Type Conversions

• Lecture 14
• Wed, Feb 18, 2004

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Topics

• Constructors as type converters
• Conversion operators

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Conversion of Types

• Frequently in a program an object must be
  converted from one type to another.
• For the built-in types, this is done
  automatically whenever it is sensible.
• Convert float to int.
• Convert int to float.
• How can it be done with created types?

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Converting to a Created Type

• A class uses its constructors to define rules for
  converting an object of another type to an object
  of that type.
• The prototype is

Class-nameClass-name(other type)
RationalRational(int) ComplexComplex(double)
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Example Convert int to Rational
// Rational constructor RationalRational(in
t n) numerator n
denominator 1 return // Usage
int i 100 Rational r r
(Rational)i r Rational(i)
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Converting to a Built-in Type

• Sometimes we want to convert an object of a
  created type to an object of a built-in type.
• For example, we might want to convert
• A Rational to a float.
• A Complex to a double.
• For this we need a conversion operator.

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Conversion Operators

• A conversion operator has prototype

Class-nameoperator built-in-type() const

• The operator converts the created-type object to
  the built-in type and returns the object of the
  built-in type.

Rationaloperator float() const Complexoperato
r double() const
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Example Convert Rational to float
Rationaloperator float() const return
(float)numerator/denominator