Templates 1. Template Functions 2. Template Class 3. Bag Class Template 4. Standard Library Template (STL) Classes Standard Library Template (STL) Classes Standard Library Template (STL) Classes 5. Vector Class

 Here’s a small function that you might write to find the maximum of two integers. int maximum(int a, int b) { if (a > b) return a; else return b; } Function Template

 Here’s a small function that you might write to find the maximum of two double numbers. int maximum(double a, double b) { if (a > b) return a; else return b; } Finding the Maximum of Two Doubles

 Suppose your program uses 100,000,000 different data types, and you need a maximum function for each... int maximum(Knafn a, Knafn b) { if (a > b) return a; else return b; } One Hundred Million Functions... int maximum(Foo a, Foo b) { if (a > b) return a; else return b; } int maximum(Poo a, Poo b) { if (a > b) return a; else return b; } int maximum(Noo a, Noo b) { if (a > b) return a; else return b; } int maximum(Moo a, Moo b) { if (a > b) return a; else return b; } int maximum(Loo a, Loo b) { if (a > b) return a; else return b; } int maximum(Koo a, Koo b) { if (a > b) return a; else return b; } int maximum(Joo a, Joo b) { if (a > b) return a; else return b; } int maximum(Ioo a, Ioo b) { if (a > b) return a; else return b; } int maximum(Hoo a, Hoo b) { if (a > b) return a; else return b; } int maximum(Goo a, Goo b) { if (a > b) return a; else return b; } int maximum(Doo a, Doo b) { if (a > b) return a; else return b; } int maximum(Coo a, Coo b) { if (a > b) return a; else return b; } int maximum(Boo a, Boo b) { if (a > b) return a; else return b; } int maximum(Knafn a, Knafn b) { if (a > b) return a; else return b; } int maximum(Foo a, Foo b) { if (a > b) return a; else return b; } int maximum(Poo a, Poo b) { if (a > b) return a; else return b; } int maximum(Noo a, Noo b) { if (a > b) return a; else return b; } int maximum(Moo a, Moo b) { if (a > b) return a; else return b; } int maximum(Loo a, Loo b) { if (a > b) return a; else return b; } int maximum(Koo a, Koo b) { if (a > b) return a; else return b; } int maximum(Joo a, Joo b) { if (a > b) return a; else return b; } int maximum(Ioo a, Ioo b) { if (a > b) return a; else return b; } int maximum(Hoo a, Hoo b) { if (a > b) return a; else return b; } int maximum(Goo a, Goo b) { if (a > b) return a; else return b; } int maximum(Doo a, Doo b) { if (a > b) return a; else return b; } int maximum(Coo a, Coo b) { if (a > b) return a; else return b; } int maximum(Boo a, Boo b) { if (a > b) return a; else return b; } int maximum(Knafn a, Knafn b) { if (a > b) return a; else return b; } int maximum(Foo a, Foo b) { if (a > b) return a; else return b; } int maximum(Poo a, Poo b) { if (a > b) return a; else return b; } int maximum(Noo a, Noo b) { if (a > b) return a; else return b; } int maximum(Moo a, Moo b) { if (a > b) return a; else return b; } int maximum(Loo a, Loo b) { if (a > b) return a; else return b; } int maximum(Koo a, Koo b) { if (a > b) return a; else return b; } int maximum(Joo a, Joo b) { if (a > b) return a; else return b; } int maximum(Ioo a, Ioo b) { if (a > b) return a; else return b; } int maximum(Hoo a, Hoo b) { if (a > b) return a; else return b; } int maximum(Goo a, Goo b) { if (a > b) return a; else return b; } int maximum(Doo a, Doo b) { if (a > b) return a; else return b; } int maximum(Coo a, Coo b) { if (a > b) return a; else return b; } int maximum(Boo a, Boo b) { if (a > b) return a; else return b; }

 This template function can be used with many data types. template Item maximum(Item a, Item b) { if (a > b) return a; else return b; } A Template Function for Maximum

 When you write a template function, you choose a data type for the function to depend upon... template Item maximum(Item a, Item b) { if (a > b) return a; else return b; } A Template Function for Maximum

 A template prefix is also needed immediately before the function’s implementation: template Item maximum(Item a, Item b) { if (a > b) return a; else return b; } A Template Function for Maximum

 Once a template function is defined, it may be used with any adequate data type in your program... template Item maximum(Item a, Item b) { if (a > b) return a; else return b; } Using a Template Function cout << maximum(1,2); cout << maximum(1.3, 0.9);...

 Here’s another function that can be made more general by changing it to a template function: int array_max(int data[ ], int n) { int i; int answer; answer = data[0]; for (i = 1; i < n; i++) if (data[i] > answer) answer = data[i]; return answer; } Finding the Maximum Item in an Array

 Here’s the template function: template Item array_max(Item data[ ], int n) { int i; Item answer; assert(n > 0); answer = data[0]; for (i = 1; i < n; i++) if (data[i] > answer) answer = data[i]; return answer; } Finding the Maximum Item in an Array

Bag Class Template Header #ifndef BAG_H #define BAG_H #define MAXIMUM_SIZE 100 template class bag { public: bag(); bag(int max); int getCount(); bool isFull(); bool isEmpty(); void remove (T item); void clear(); void display();... private: T *data; int count; int capacity; }; #include bag.template // Note #endif

Bag Class Template Implementation #include #include "bag.h" using namespace std; template bag ::bag(){ capacity = MAXIMUM_SIZE; data = new T [capacity; count = 0; } template bag ::bag(int max){ capacity = max; data = new T [capacity]; count = 0; }... template int bag ::getCount(){ return count; } template bool bag ::isFull(){ return count == capacity; } template bool bag ::isEmpty(){ return count == 0; }...

Client Program for Bag Template #include #include "bag.h" using namespace std; int main() { // Check with int bag iBag; int iList[] = {2, 4, 6}; int iCount = 3; for (int i = 0; i < iCount; i++){ iBag.insert(iList[i]); } cout << "Int bag contents: "; iBag.display(); cout << endl; iBag.remove(iList[0]); cout << "After removing: “; iBag.display(); cout << endl;... // check with string bag sBag; string sList[] = {"Anne", "Bill", "Cathy"}; int sCount = 3; for (int i = 0; i < sCount; i++){ sBag.insert(sList[i]); } cout << "String contents: "; sBag.display(); cout << endl; sBag.remove(sList[0]); cout << "After removing: “; sBag.display(); cout << endl; system("PAUSE"); return EXIT_SUCCESS; }

Some STL Class Templates vector Array list Doubly-linked list slist Singly-linked list queue FIFO (first-in, first-out) structure deque Array-like structure, with efficient insertion and removal at both ends set Set of unique elements stack LIFO (last in, first out) structure More templates

Your Turn  Among the member functions in the vector class template provided by STL are:  vector()—constructor  void push_back(T item)—insert at back  T operator[](int i)—returns item at position i (as in array)  int size()—return number of items in vector  Using the template, write a short program which inserts 3 string items in a vector and prints out its contents.

Solution #include using namespace std; int main(){ vector v; v.push_back("Alice"); v.push_back("Brad"); v.push_back("Chad"); for (int i = 0; i < 3; i++){ cout << v[i]<< endl; } system("PAUSE"); return EXIT_SUCCESS; }

 A template function depends on an underlying data type.  More complex template functions and template classes are discussed in Chapter 6. Summary