Lecture 8

• classes • Introduction to the Standard Template Library (STL) –Containers • vector • map – – Algorithms

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Class Templates • Class templates •Specify entire range of related classes •Generic programming – Class-template specializations •Example: Stack See tstack1.h •LIFO (last-in-first-out) structure •Describe notion of stack generically •Instantiate type-specific version template< class T > Class Stack { … } //end class stack Lec 5 Programming in C++ 2

1 Class Templates • Member functions (methods) template< class T > bool Stack< T >::push(const T &value) {…} Binds function definition to the class template

• To create a stack of doubles Stack< double > doubleStack(5); doubleStack.push(5.6); See Fig11_03.cpp

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Class Templates and Nontype Parameters template< class T = String, int elements > class Stack { private: int size; Default type int top; T stackHolder[elements]; public: … } //end class stack

Stack< double, 100 > myStack;

Think: What is a advantage of this solution?

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2 Standard Template Library

• Powerful, template-based components • Containers: template data structures – Objects that contain other objects • Iterators: like “pointers”, cycle through the contents of a container • Algorithms: manipulate containers, searching, sorting, etc. •Code reuse – Templates are used •Performance • STL specification requires that containers and algorithms be implemented in a way that ensures optimal run time performance.

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Containers • Several types of containers – Sequence containers •Linear data structures – – Linear list – Associative containers •Store key/value pairs •Retrieve a value given its key – Container adapters • Transform the functionality of a container • A container automatically grows when elements are added and shrinks when elements are removed.

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3 Containers • Sequence containers – vector A dynamic array – deque A double-ended queue – list A linear list • Associative containers – no duplicates – multiset duplicates allowed – map Associates one value for each key – multimap Associates multiple values for each key •Container adapters – stack – queue template > class queue – priority_queue Lec 5 Programming in C++ 7

vector Sequence Container • vector // vector class-template definition #include – Data structure with contiguous memory locations •Access elements with [] – Use when data is accessed randomly • When memory exhausted – Allocates larger, contiguous area of memory – Copies itself there –Deallocatesold memory • Has random access iterators Lec 5 Programming in C++ 8

4 vector Sequence Container • Declarations vector v1; //create a zero-length int vector vector v2(20); vector v3(5, ‘x’); vector v4(v1); • Subscripting [] v3[6] = ‘b’; //Error!! – Access out of bounds (silent error) – Will not increase vector size • Expanding the vector v1.push_back(8); //memory is allocated cout << v1.size();// display number of elements stored v1.pop_back();

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Vector Example

main(){ vector SS; SS.push_back("The number is 10"); SS.push_back("The number is 20"); SS.push_back("The number is 30"); cout << "Loop by index:" << endl; int ii; for(ii=0; ii < SS.size(); ii++) { cout << SS[ii] << endl; } return 0; }

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5 Iterators • Iterators similar to pointers – operators same for all containers • * dereferences • ++ points to next element – Create an iterator given a container c • c.begin() returns iterator to first element • c.end() returns iterator to after last element – Container adapters do not support iterators Lec 5 Programming in C++ 11

Iterator Categories

• Input – Retrieve, but not store values. Forward moving only. • Output – Store, but not retrieve. Forward moving only. • Forward – Store and retrieve values. Forward moving only. • Bidirectional – Store and retrieve values. Forward and backward moving. • Random access – Store and retrieve values. Elements can be accessed randomly.

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6 Iterator Operations • All – ++p, p++ • Input, bidirectional, and random iterators – *p – p = p1 – p == p1, p != p1 • Output iterators – *p = … – p = p1 • Input iterators – x = *p – p = p1 – p-> – p == p1, p != p1

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Iterator Operations • Bidirectional – --p, p-- • Random access – p + i, p += i – p - i, p -= i – p[i] – p < p1, p <= p1 – p > p1, p >= p1

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7 Iterators Example main(){ vector SS; //add elements to SS vector::const_iterator cii; for(cii=SS.begin(); cii!=SS.end(); cii++) { cout << *cii << endl; } //Reverse Iterator vector::reverse_iterator rii; for(rii=SS.rbegin() ; rii!=SS.rend() ; ++rii) { cout << *rii << endl; } return 0; }

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Const and reverse Iterators

• Iterators std::vector::const_iterator iterVar; • const_iterator cannot modify elements

std::vector::reverse_iterator iterVar; •Visits elements in reverse order (end to beginning) •Use iterVar.rbegin() to get starting point •Use iterVar.rend() to get ending point

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8 vector Sequence Container • vector functions – v.push_back(value) • Add element to end (found in all sequence containers). – v.size() • Current number of elements stored in the vector – v.capacity() • How much vector can hold before reallocating memory – vector v(a, a + SIZE) •Creates vector v with elements from array a up to (not including) a + SIZE

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vector Sequence Container • vector functions – v.insert(iterator, value ) •Inserts value before location of iterator – v.insert(iterator, array , array + SIZE) • Inserts array elements (up to, but not including array + SIZE) into vector before iterator – v.erase( iterator ) • Remove element pointed by iterator from container – v.erase( iter1, iter2 ) • Remove elements starting from iter1 and up to (not including) iter2 – v.clear() • Erases entire container

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9 vector Sequence Container

• vector functions – v.front(), v.back() • Return a reference to the first and last element – v[index] = value; • Assign value to an element – v.at(index) = value; •As above, with range checking • out_of_bounds exception See Fig21_14.cpp

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Common STL typedefs • typedefs for first-class containers – const_reference – reference

– pointer vector v(10); – iterator vector::reference ref = v.begin(); – const_iterator – reverse_iterator – const_reverse_iterator – value_type – …

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10 Algorithms • STL has algorithms used generically across containers – Operate on elements indirectly via iterators • #include – Often operate on a range of elements •Defined by pairs of iterators – Algorithms often return iterators • find() •Returns iterator to element, or end() if not found – Pre-made algorithms save programmers time and effort See Fig21_15.cpp Lec 5 Programming in C++ 21

Algorithms Example bool even(int n) { return (n % 2? false: true); } int main(){ int array[6] = { 1, 2, 3, 4, 5, 6 }; vector b(array, array+6); int c = count_if(b.begin(), b.end(), even); cout << "Number of evens: " << c << endl; vector x(5, 0); // It only copies values 1,2,3,4 copy(b.begin(), b.end(), ++x.begin()); reverse(x.begin(), x.end()); vector::iterator ptr; for(ptr = x.begin(); ptr != x.end(); ++ptr ) cout << *ptr << ' '; // Output looks like: 4 3 2 1 0 } Lec 5 Programming in C++ 22

11 Types of Algorithms •Copying • Searching unsorted sequences • Replacing and removing elements • Reordering a sequence •Sorting • Sorted Sequence Searching • Merging sorted sequences • Set operations • Heap operations • Minimum and maximum •Permutations • Miscellaneous

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Stream Iterators

• Possible to view I/O streams as another type of container • #include • Input streams: istream_iterator • To read values into the sequence in a type safe manner • Operators: ->, *, ++ • Output streams: ostream_iterator • To write values into the sequence in a type safe manner • Operators: =, *, ++

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12 istream_iterator

std::istream_iterator inputInt(cin) •Can read input from cin • *inputInt – Dereference to read first int from cin • ++inputInt –Go to next int in stream

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istream_iterator and Algorithms int main() { vector v(5);

cout << "Enter 5 integers." << endl; istream_iterator int_itr(cin); copy(int_itr, istream_iterator(), v.begin());

for(int i = 0; i < v.size(); i++) cout << v[i] << " "; } End-of-stream: – istream_iterator() –End-of-file (ctrl-Z) for cin

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13 ostream_iterator

std::ostream_iterator outputInt(cout) •Can output intsto cout • *outputInt = 7 –Outputs 7 to cout • ++outputInt – Advances iterator so we can output next int

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ostream_iterator and Algorithms std::vector v; std::vector::iterator it; std::ostream_iterator output(cout, " " ); for(it = v.begin(); it != v.end(); ++it) cout << *it << endl; std::copy(v.begin(), v.end(), output );

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14 Usage of ostream_iterator • ostream_iterator – std::ostream_iterator< type > Name( outputStream, separator ); • type: outputs values of a certain type • outputStream: iterator output location • separator: separating outputs •Example std::ostream_iterator output(cout, " " ); std::copy( iterator1, iterator2, output ); • Copies elements from iterator1 up to (not including) iterator2 to output, an ostream_iterator

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Numeric Algorithms

#include int main() { vector v(5);

cout << "Enter 5 integers." << endl; istream_iterator int_itr(cin); copy(int_itr, istream_iterator(), v.begin());

// print sum between adjacent elements adjacent_difference(v.begin(), v.end(), ostream_iterator(cout," "), plus()); }

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15 map container • Associative container in which keys are mapped with values – A stored valued can be retrieved by its key • Key: person name • Value: telephone number – multimap container allows non unique keys • Key: City name • Value: list of clients who live in the city

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map Example Student name Grade

typedef std::map myList; myList grade_list; grade_list["John"] = 'A'; if(grade_list.find("Tim") == grade_list.end()) std::cout<<"Tim is not in the map!"<< endl; // Should be John std::cout<first<< endl; // Should be A std::cout<second<< endl;

grade_list.insert(myList::value_type("David”, ‘B’)); grade_list.insert(make_pair("David”, ‘B’));

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