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Algorithms and Functionals

Section 1.6.4, class notes, STL references

Standard Template Library

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Standard Template Library Features

• Algorithms

• Functionals

• Containers

• Iterators

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Algorithms• Include <algorithm>

– find, for_each, sort, min, max, etc– Example: Lec10/alg.cpp

void PrintArray(int *A, int Size){for(int i=0; i< Size; i++) cout << A[i] << " ";}

int main(){ const int ASize = 8; int A[ASize] = {32, 4, 8, 62, 3, 42, 23, 9};

PrintArray(A,ASize); sort(A, A+ASize); PrintArray(A,ASize); reverse(A, A+ASize); PrintArray(A,ASize);}

Output32 4 8 62 3 42 23 9

3 4 8 9 23 32 42 62

62 42 32 23 9 8 4 3

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for_each• See files included from:

– /usr/local/include/c++/4.3.2/algorithm

template<typename _InputIterator, typename _Function> _Function for_each(_InputIterator __first, _InputIterator __last, _Function __f) {__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>) __glibcxx_requires_valid_range(__first, __last); for (; __first != __last; ++__first) __f(*__first); return __f; }

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for_each Simplified

template<typename _InputIterator, typename _Function> _Function for_each(_InputIterator __first, _InputIterator __last, _Function __f) {__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>) __glibcxx_requires_valid_range(__first, __last); for (; __first != __last; ++__first) __f(*__first); return __f; }

template<typename I, typename F> F for_each(I first, I last, F f) { for (; first != last; ++first) f(*first); return f; }

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for_each Example

class print{public: void operator()(int a) { cout << a << " "; }};

• Lec10/fo.cpp– print is a function class

• It overloads operator()

for_each(A, A+ASize, print());cout << "\n";

sort(A, A+ASize); for_each(A, A+ASize, print());cout << "\n";

reverse(A, A+ASize); for_each(A, A+ASize, print()); cout << "\n";

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Another Function Class Example

class gt{public: bool operator()(int a, int b) { return a > b; }};

• Lec10/fo2.cpp– Use a function object to sort in descending order

for_each(A, A+ASize, print());cout << "\n";

sort(A, A+ASize, gt()); for_each(A, A+ASize, print());cout << "\n";

Output32 4 8 62 3 42 23 9

62 42 32 23 9 8 4 3

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Functionals• They are function classes provided by STL

– Include <funtional>– less, greater, etc– Example: Lec10/fo3.cpp

for_each(A, A+ASize, print());cout << "\n";

sort(A, A+ASize, greater<int>()); for_each(A, A+ASize, print());cout << "\n";

Output32 4 8 62 3 42 23 9

62 42 32 23 9 8 4 3