Understanding Generic Algorithms and Templates in Programming

1. Chapter 17 Templates

2. Generic Algorithms Algorithms in which the actions or steps are defined, but the data types of the items being manipulated are not.

3. Examples Of Generic Algorithm • Swap the values of two variables of the same data types • Find the index of the smallest value in an array. • Pair up 2 values • Linked list

4. Overloading functions for Generic Algorithms void swap (char& v1, char& v2) { char temp = v1; v1 = v2; v2 = v3; } void swap (int& v1, int& v2) { int temp = v1; v1 = v2; v2 = v3; } void double (double & v1, double & v2) { double temp = v1; v1 = v2; v2 = v3; } void swap (CAny& v1, CAny& v2) { CAny temp = v1; v1 = v2; v2 = v3; }

5. Template for Functions template <class T> void swap (T& v1, T& v2) { T temp = v1; v1 = v2; v2 = v3; } int main () { int i1=1, i2=2; swap (i1, i2); char c1=‘a’, c2=‘A’; swap (c1, c2); }

6. Template Function Notes • The words template <class T> tell the compiler this is a template for a generic data type T and that T is the parametized type which can be replaced by a defined data type. • T must have all of the operations used in the template function. int a[5], b[5]; … // Some code to fill up arrays swap (a, b); // NO! There is no assignment operator for arrays

7. Class Template //Class template for a pair of values of type T template <class T> class Pair { public: Pair(); Pair(T f, T s); void setElement (intpos, T val); T getElement (intpos); private: T first; T second; };

8. Class Template (cont.) template <class T> Pair<T>::Pair() {} template <class T> Pair<T>::Pair(T f, T s) { first = f; second = s; } template <class T> void Pair<T>::setElement (intpos, T val) { if (pos == 1) first = val; else second = val; } template <class T> T Pair<T>::getElement (intpos) { if (pos == 1) return first; else return second; } void main () { Pair<int> scores; Pair<char>seats(‘A’, ‘B’); score.setElement(1, 3); score.setElement(2, 5); char mySeat mySeat=seats.getElement(1); }

9. Class Template Notes • The words template <class T> tell the compiler this is a template for a generic data type T and that T is the parametized type which can be replaced by a defined data type. • T is used as a type in all function definitions or parameters of the class template. • You can use typedef to improve readability. typedef Pairs<int> PairsOfInt; then declare PairsOfInt score; • Type T is specialized by giving a type argument to the class name in place of the T.