STL Vector

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STL Vector

• Dr. Ying Xie

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STL Introduction

• The STL (Standard Template Library) consists of
  10 container classes with three categories
• sequence containers
• stores data by position in linear order
• vector, deque, list
• adapter containers
• contains another container as its underlying
  storage structure
• stack, queue, priority_queue
• associative containers
• stores elements by key, such as name, social
  security number, or part number
• set, multiset, map, multimap

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STL Vector API

• The STL container Vector - API
• Constructors
• vector()
• vector(int n, const T value T())
• vector(T first, T last)
• initialize the vector using the address range
  first, last)
• Operations (p.201)
• T back() // return the value of the item at the
  rear
• const T back() const // constant version of
  back()
• bool empty() const
• T operator (int i)
• const T operator (int i) const // constant
  version
• void push_back(const T value)
• void pop_back()
• void resize(int n, const T fill T())
• int size() const

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The STL container Vector - constructor

• The first version of constructors
• vector()
• no argument is included
• the resulting vector is empty, with size of 0
• vectorltdoublegt dblVector
• vectorltstringgt v

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The STL container Vector - constructor

• The second version of constructors
• vector(int n, const T value T())
• with one argument of size with the default value
  of T()
• vectorltintgt intVector(5) // initial value is
  int()
• vectorltstringgt strVector(10) // all
• with two arguments of size and initial value
• vectorltchargt line(80, ) // all bland char
• vectorltAccountgt accounts(7, Account(, , 0))

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The STL container Vector - constructor

• A third version of the vector constructor
• vector(T first, T last)
• initialize its values from an array
• int intArray5 9, 2, 7, 3, 12
• vectorltintgt intVector(intArray, intArray5)
• the array address
• the array name intArray is the address of
  intArray0
• intArray1 is the address of intArray1
• a generic code
• int intArray 9, 2, 7, 3, 12
• int arrSize sizeof(intArray)/sizeof(int)
• vectorltintgt intVector(intArray,
  intArrayarrSize)

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The STL Vector - Adding and Removing

• Operations to modify the rear of the vector
• push_back()
• adds an element of type T at the rear of the
  vector
• it grows the size of the vector
• cout ltlt v.back() // assume it is u
• v.push_back(w)
• v.back() y
• pop_back()
• deletes the last element in the vector at index
  (size()-1)
• reduces the size by 1

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The STL container Vector - Resizing

• The function void resize(int n, const T fill
  T())
• uses the argument n to change the size of the
  vector and
• uses the second argument to be the fill value
• if the new size is greater than the current size
• the vector grows by adding n-size() new elements
• all of the exiting elements remain fixed
• the new elements are assigned the fill value
• if the new size is less than the current size
• it chops off elements at the tail of the vector
• the first n elements remain fixed
• the vector discards the other size()-n elements

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Example of using STL vector

• include ltiostreamgt
• include ltvectorgt
• using namespace std
• int main()
• vectorltintgt v1
• cout ltlt "the size of v1 at t0 is
  "ltltv1.size()ltltendl
• v1.push_back(1)
• v1.push_back(2)
• v1.push_back(3)
• cout ltlt "the size of v1 at t1 is " ltlt
  v1.size() ltltendl
• for (int i0 ilt v1.size() i)
• cout ltlt v1i ltlt " "
• cout ltlt endl
• cout ltlt v1.back() ltltendl

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Join one vector to another

• template lttypename Tgt
• void join (vectorltTgt vA, const vectorltTgt vB)
• // capture the size of vB in sizeB
• int i, sizeB vB.size()
• // use index i to access the elements of vB and
  push_back()
• // to add the elements to the rear of vA
• for (i 0 i lt sizeB i)
• vA.push_back(vBi)

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Insertion Sort (1) - Illustration
pass 1
5
2
6
1
2
5
6
1
pass 2
2
5
6
1
2
5
6
1
pass 3
2
5
6
1
1
2
5
6
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Insertion Sort (2)

• template lttypename Tgt
• void insertionSort(vectorltTgt v)
• int i, j, n v.size()
• T target
• for (i 1 i lt n i)
• j i
• target vi
• while (j gt 0 target lt vj-1)
• vj vj-1
• j--
• vj target

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Insertion Sort (3)

• Time Complexity
• T(n) 1/2 2/2 3/2 (n-2)/2 (n-1)/2
  n(n-1)/4
• O(n2)