STL: C Standard Library (continued)

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STL C Standard Library(continued)
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STL Iterators

• Iterators are allow to traverse sequences
• Methods
• operator
• operator-gt
• operator, and operator
• Different types of iterators - to support read,
  write and random access
• Containers define their own iterator types
• Changing the container can invalidate the iterator

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Iterator Types

• Output write only and can write only once
• Input read many times each item
• Forward supports both read and write
• Bi-directional supports also decrement
• Random supports random access (just like C
  pointer)

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Iterators Containers

• Bidirectional iterators
• list, map, set
• Random access iterators
• vector, deque
• Input/output/forward iterators
• iostreams

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Iterators Containers

• Every STL container T provides
• class T
• typedef iterator // iterator type T
• iterator begin() // first element of the
  container
• iterator end( // element after last of the
  container

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Iterators Containers

• Typical code will look like
• Container C
• Containeriterator i
• for( i C.begin() i ! C.end() i)
• // do something with i

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Iterators Containers

• Iterators allow to access/modify elements
• Container C
• Containeriterator i,j
• C.insert(i,x) insert x before i
• C.insert(i,first,last) insert elements in
  first,last) before i
• C.erase(i) erase element i points to
• C.erase(i,j) erase elements in range i,j)

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Iterator validity

• When working with iterators, we have to remember
  that their validity can change
• Whats wrong with this code?
• Container C
• Citerator i
• for( i C.begin() i ! C.end() i )
• if( f( i ) ) // some test
• C.erase(i) // remove this element

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Iterator validity

• Two cases
• list, set, map
• i is not a legal iterator
• vector
• i points to the element after
• In either case, this is not what we want

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Iterator validity

• Second try
• Container C
• Citerator i C.begin()
• while( i ! C.end() )
• Citerator j i
• if( f( j ) ) // some test
• C.erase(j) // remove this element
• Works for set, map, list, not vector or deque

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Iterators and Map

• Suppose we work with
• mapltstring,intgt dictionary
• mapltstring,intgtiterator i
• i dictionary.begin()
• What is the type of i ?

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Iterators and Map

• Every STL container type Container defines
• Containervalue_type
• Type of elements stored in container
• This is the type returned by an iterator
• Containervalue_type
• Containeriterator operator()

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Iterators and Map

• Ok, so what type of elements does a map return?
• Recall
• mapltKeyType,ValueTypegt keeps pairs
• KeyType key key of entry
• ValueType value value of entry

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Pairs

• templatelt class T1, class T2gt
• struct pair
• typedef T1 first_type
• typedef T2 first_type
• T1 first
• T2 second
• pair( const T1 x, const T2 y )
• first(x), second(y)

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Map value_type

• templatelt class Key, class T,
• class Cmp lessltKeygt gt
• class map
• public
• typedef pairltconst Key, Tgt value_type
• typedef Key key_type
• typedef T mapped_type
• typedef Cmp key_compare

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Using map iterator

• mapltstring,intgt dict
• mapltstring,intgtiterator i
• for( i dict.begin()
• i ! dict.end()
• i )
• cout ltlt i-gtfirst ltlt
• ltlt i-gtsecond ltlt \n
• See dictionary.cpp

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Iterators and Assoc. Containers

• Additional set of operations
• iterator Cfind(key_type const key)Return
  iterator to first element with key. Return end()
  if not found
• iterator Clower_bound(key_type const
  key)Return iterator to first element greater or
  equal to key
• iterator Cupper_bound(key_type const
  key)Return iterator to first element greater
  than key

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Iterators Streams

• Can access iostreams through iterators
• istream_iteratorltstringgt in(cin)
• istream_iteratorltstringgt endOfInput
• ostream_iteratorltstringgt out(cout)
• while( in ! endOfInput )
• string s in
• out s
• out
• see useStreamIterators.cpp

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Inserters

• istream_iteratorltstringgt in(cin)
• istream_iteratorltstringgt endOfInput
  vectorltstringgt vect
• back_insert_iteratorltvectorltstringgt gt
• back(vect)
• // copy input words into vector
• while( in ! endOfInput )
• back in
• // same as vect.push_back(in)

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Inserters

• Inserters are output iterators
• back_insert_iteratorltCgt( C c)
• Insert at back of c
• front_insert_iteratorltCgt( C c)
• Insert at front of c
• insert_iteratorltC,Itergt(C c, Iter i)
• Insert at just before i
• Allow to write into containers in generic
  algorithms

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Do-it-yourself iterators

• You can create iterators
• Check list
• Define the appropriate operators
• Ensure copy constructor/operator
• Define the right typedefsuse inheritance from
  iteratorlt..gt class
• See TokenIterator.h

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Sequence Adapters

• Adapters of basic containers
• Very easy, but limited interface
• stackltT,Seqgt
• provides push, pop, top, size and empty
• queueltT,Seqgt
• also provides back
• priority_queueltT,Seq,Cmpgt
• provides same interface as stack
• uses a compare function object

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Container summary
List ops Front ops Back ops Iterators
vector const n const Random
list const const const Bi-direct
deque const n const const Random
stack const
queue const const
priority_queue log(n) log(n)
map log(n) log(n) Bi-direct
set log(n) Bi-direct
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Algorithms Overview

• Sequence operations
• Non modifying for_each, find, count, search,
  mismatch, equal
• Modifying transform, copy, swap, replace, fill,
  generate, remove, unique, reverse, rotate,
  random_shuffle
• Sorted sequences operations
• sort, lower_bound, upper_bound, equal_range,
  binary_search, merge, includes, set_union,
  intersection, difference, symmetric_difference

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Algorithms

• Most STL algorithms works on sequences
• Sequences are passed as two iterators
• beginning element
• element one after last
• Algorithms depend on iterator type
• not on container type

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Copy

• templatelt class In, class Outgt
• Out copy(In first, In last, Out res)
• while (first ! last)
• res first
• return res
• See useCopy.cpp

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Non-modifying Sequence Algorithms

• In find(In first, In last, const T val)
• find the first occurence of val in the sequence
• In find_if(In first, In last, Pred p) find the
  first element satisfying p
• I1 find_first_of(I1 f1, I2 l1, I2 f2, I2 l2)
  find the first match between two sequences.
• I1 search( I1 f1, I1 l1, I2 f1, I2 l2 )search
  for the sequence f2...l2 inside f1..l1

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Sorted Sequence Algorithms

• sort(In first, In last, class cmp)
• find the first occurence of val in the sequence
• In lower_bound(In first, In last,
  T const val, class cmp) find the first
  element not less than val
• bool binary_search(In first, In last,
  T const val, class cmp) check if val
  appears in the sequence
• Out merge( I1 f1, I1 l1, I2 f1, I2 l2,
  Out out )merge two sorted sequences and write
  the merged sequence onto the output iterator out

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Ex4 Interactive Graph Operations

• An interactive shell that allows to perform graph
  operations
• Gcalcgt G1 x11, x22 ltx11, x22gt Gcalcgt G2
  x11, x22 ltx11, x22gt
• Gcalcgt G3 G1G2
• Gcalcgt print G3

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Ex5 Preview

• Extend the graph calculator
• Weighted graphs
• Algorithms shortest path, minimum spanning tree,
  max flow, etc.
• Load/Save file

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Ex4 Components

• Graph data structure
• Symbol Table
• Command parser
• Command evaluater
• Emphasis extendibility of command syntax for
  next exercise

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Graph Data Structure

• Your design show allow to
• Constructors/copy etc.
• Add vertices/edges
• Iterate over vertices
• Iterate over parents of a vertex
• Iterate over children of a vertex
• Graph operations