Dr. Yingwu Zhu

STL Vector and Iterators

STL (Standard Template Library)

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A library of class and function templates

Components:1.Containers:

• Generic "off-the-shelf" class templates for storing collections of data

2.Algorithms: • Generic "off-the-shelf" function templates for operating

on containers

3.Iterators: • Generalized "smart" pointers that allow algorithms to

operate on almost any container (access container elements)

STL’s 10 Containers, p474

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Kind of Container STL ContainersSequential: deque, list, vector

Associative: map, multimap,

multiset, set

Adapters: priority_queue, queue, stack

Non-STL: bitset, valarray, string

The vector Container

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A type-independent pattern for an array class (dynamic array-based)capacity can expandself contained

Declarationtemplate <typename T>class vector { public: . . .private: T* myArray;

} ;

The vector Container

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Constructors

vector<T> v, // empty vector

v1(100), // 100 elements of type T

v2(100, val), // 100 copies of val

v3(fptr,lptr); // contains copies of // elements in memory

// locations fptr to lptr

Exercises? Examples?

vector Operations

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Information about a vector's contentsv.size()v.empty()v.capacity()//expand by doubling its size

v.reserve()//grow its capacity to paraAdding, removing, accessing elements

v.push_back()v.pop_back()v.front()//return a reference to v’s first itemv.back()

vector Operations

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Assignmentv1 = v2

Swappingv1.swap(v2)

Relational operators == implies element by element equalityless than < behaves like string comparison

Exercises

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vector v; //right or wrong? Why?

Exercises

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vector<double> v;cout << v.capacity() << " " << v.size() << endl;

vector<int> v(3); cout << v.capacity() << " " << v.size() << endl;

vector<int> v(4, 5); cout << v.capacity() << " " << v.size() << endl;

vector<int> v;v.push_back(9); v.push_back(8); v.push_back(7);cout << v.capacity() << " " << v.front() << endl;

Iterators

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Note from table 9.3 that a subscript operator is provided, p478BUT … this is not a generic way to access

container elementsSTL provides objects called iterators

can point at an elementcan access the value within that elementcan move from one element to another

They are independent of any particular container … thus a generic mechanism

Iterators

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Given a vector which has had values placed in the first 4 locations:

v.begin() will return the iterator value for the first slot,

v.end() for the next empty slot

9 4 15 3

vector<int> v

v.begin()v.begin() v.end()v.end()

Iterators

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Each STL container declares an iterator typecan be used to define iterator objects

To declare an iterator objectthe identifier iterator must be preceded by

name of containerscope operator ::

Example:vector<int>::iterator vecIter = v.begin()

Iterators

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Basic operators that can be applied to iterators:increment operator ++decrement operator --dereferencing operator *Assignment =Addition, subtraction +, -, +=, -=vecIter + n returns iterator positioned n elements away

Subscript operator [ ]vecIter[n] returns reference to nth element from current position

Iterators

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Contrast use of subscript vs. use of iteratorostream & operator<<(ostream & out, const vector<double> & v){ for (int i = 0; i < v.size(); i++) out << v[i] << " "; return out;}

for (vector<double>::iterator it = v.begin(); it != v.end(); it++) out << *it << " ";

Exercise: output?

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vector<double> v;for (int i=2; i<=5; i++)

v.push_back(1.1 * i);cout << v.capacity() << “ “ << v.size() << endl;vector<double>::iterator it, it1, it2;for (it = v.begin(); it != v.end(); it++)

cout << *it << “ “;cout << endl;it1 = v.begin(); it2 = v.end();*it1 = 8.8; *(it2-1) = 9.9;for (it = v.begin(); it != v.end(); it++)

cout << *it << “ “;cout << endl;it1 += 2; it2--;cout << it1[1] << “ “ << it2[-1] << endl;

Lecture Review

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Know containers such as vectorLike an array, but no need to worry about

capacityGeneric arrays, can be instantiated with any data

typesFamiliar with basic operations

Iterators provide a generic way to access elements in a container

Like a pointer, generic pointerUse when bundled with a container