Iterators

1
Iterators

• Andy Wang
• Data Structures, Algorithms, and Generic
  Programming

2
Iterators Overview

• Provide access to container elements
• Provide interface between generic algorithms and
  containers
• Proper type
• Uniform public interface across variety of
  containers

3
Iterators Overview (2)

• Classify iterators by public interface
  functionality
• input and output iterators
• forward iterators
• bidirectional iterators
• random access iterators
• adaptor iterators
• Specialize iterators to containers with
  implementation

4
Forward Iterators

• // comparison logic
• bool operator(const Iterators ) const
• bool operator!(const Iteartor) const
• // element access
• value_type operator() const
• // motion
• Iterator operator()
• Iterator operator(int)
• // proper type
• Iterator()
• Iterator()
• Iterator Iterator(const Iterator)
• Iteartor operator(const Iterator)

5
Forward Iterators

• Minimum public interface
• ContainerIterator I
• for (I C.Begin() I ! C.End() I)
• cout ltlt I

6
Bidirectional Iterators

• Forward iterator with more motion
• // motion
• Iterator operator()
• Iterator operator(int)
• Iterator operator--()
• Iterator operator--(int)

7
Random Access Iterators

• Bidirectional iterator with random accesses
• // bracket operator
• T operator (unsigned int i) const
• // pointer arithmetics
• long operator-(const Iterator I2) const // n I
  I2
• Iterator operator(long n) const // I2 I n
• Iterator operator(long n)
• Iterator operator-(long n)
• // similar declarations of last three for all
  other integral types

8
Input Iterators

• Specialized read-only forward iterator
• // comparison logic
• bool operator(const Iterators ) const
• bool operator!(const Iteartor) const
• // element access
• const value_type operator() const
• // motion
• Iterator operator()
• Iterator operator(int)
• // proper type
• Iterator()
• Iterator()
• Iterator Iterator(const Iterator)
• Iteartor operator(const Iterator) // no
  assignment operator

9
Example

• g_copy
• template ltclass I, class Jgt
• void g_copy(I source_begin, I source_end, J
  dest_begin)
• while (source_begin ! source_end)
• dest_begin source_begin

10
Output Iterators

• Specialized write-only forward iterator
• // no comparison logic
• // write-only element access
• Iterator operator() const
• // motion
• Iterator operator()
• Iterator operator(int)
• // proper type
• Iterator()
• Iterator()
• Iterator Iterator(const Iterator)
• // no assignment operator

11
The Iterator Hierarchy

• Enforced by discipline in design
• Not inheritance

Input Iterators
Output Iterators
Forward Iterators
Bindirectional Iterators
Random Access Iterators
12
Iterator Adaptors

• Insert iterators
• Adaptee a container class
• Adaptor an output iterator
• Utility replace overwrite with insert in
  generic algorithms
• Stream iterators
• Adaptee an istream/ostream class
• Adaptor an input/output iterator
• Utility read/write directly from/to
  istream/ostream in generic algorithms

13
Iterator Adaptors (2)

• Reverse iterators
• Adaptee an iterator class
• Adaptor an iterator of the same category
• Utility normal direction of increment/decrement
  is reversedapplies generic algorithms in reverse
  direction

14
Insert Iterators

• template ltclass Cgt
• class PushBackIterator
• public
• explicit PushBackIterator(C x)Cptr(x)
• PushBackIteratorltCgt operator(const typename
  Cvalue_type t)
• Cptr-gtPushBack(t)
• return this
• PushBackIteratorltCgt operator() return
  this
• PushBackIteratorltCgt operator() return
  this
• PushBackIteratorltCgt operator(int) return
  this
• protected
• C Cptr
• // usage
• TListltchargt L
• PushBackIterator ltTList ltchargt gt Litr(L)