Templates

1.1. Template FunctionsTemplate Functions2.2. Template ClassTemplate Class3.3. Bag Class TemplateBag Class Template4. Standard Library Template (STL) Classes5.5. Vector ClassVector 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 <class Item>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 <class Item>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 <class Item>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 <class Item>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 <class Item>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 T>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 <iostream> #include "bag.h"using namespace std;

template<class T>bag<T>::bag(){ capacity = MAXIMUM_SIZE; data = new T [capacity; count = 0;}

template<class T>bag<T>::bag(int max){ capacity = max; data = new T [capacity]; count = 0;} . . .

. . .template<class T>int bag<T>::getCount(){ return count;}template<class T>bool bag<T>::isFull(){ return count == capacity;} template<class T>bool bag<T>::isEmpty(){ return count == 0;}. . .

Client Program for Bag Template#include <iostream>#include <string>#include "bag.h"using namespace std;int main() { // Check with int bag<int> 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<string> 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 Arraylist Doubly-linked listslist Singly-linked listqueue FIFO (first-in, first-out) structuredeque Array-like structure, with efficient insertion

and removal at both endsset Set of unique elementsstack LIFO (last in, first out) structure

More templates

Your Turn

Among the member functions in the Among the member functions in the vector vector class class template provided by STL are:template provided by STL are: vector()—constructorvector()—constructor void push_back(T item)—insert at backvoid push_back(T item)—insert at back T operator[](int i)—returns item at position i (as in array)T operator[](int i)—returns item at position i (as in array) int size()—return number of items in vectorint size()—return number of items in vector

Using the template, write a short program which Using the template, write a short program which inserts 3 string items in a vector and prints out its inserts 3 string items in a vector and prints out its contents.contents.

Solution#include <iostream>#include <string>#include <vector>using namespace std;

int main(){ vector<string> 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