EECE 330 Chapter, Fall 2011

H. Artail Templates Outline 12.1 Introduction 12.2 Function Templates 12.3 Overloading Template Functions 12.4 Class Templates 12.5 Class Templates and Non-type Parameters 12.6 Templates and Inheritance 12.7 Templates and friends 12.8 Templates and static Members H. Artail 12.1 Introduction • Templates - easily create a large range of related functions or classes – function template - the blueprint of the related functions – template function - a specific function made from a function template H. Artail 12.2 Function Templates • overloaded functions – perform similar operations on different data types • function templates – perform identical operations on different data types – provide type checking • Format: template<class type, class type...> – can use class or typename - specifies type parameters template< class T > template< typename ElementType > template< class BorderType, class FillType > – Function definition follows template statement H. Artail 12.2 Function Templates (II) 1 template< class T > 2 void printArray( const T *array, const int count ) 3 { 4 for ( int i = 0; i < count; i++ ) 5 cout << array[ i ] << " "; 6 7 cout << endl; 8 } The int version of printArray is void printArray( const int *array, const int count ) { for ( int i = 0; i < count; i++ ) cout << array[ i ] << " "; cout << endl; } T is the type parameter. T's type is detected and substituted inside the function. The newly created function is compiled. H. Artail 1 // Fig 12.2: fig12_02.cpp 2 // Using template functions 3 #include <iostream> 4 5 using std::cout; 6 using std::endl; 7 8 template< class T > 9 void printArray( const T *array, const int count ) 10 { 11 for ( int i = 0; i < count; i++ ) 12 cout << array[ i ] << " "; 13 14 cout << endl; 15 } 16 17 int main() 18 { 19 const int aCount = 5, bCount = 7, cCount = 6; 20 int a[ aCount ] = { 1, 2, 3, 4, 5 }; 21 double b[ bCount ] = { 1.1, 2.2, 3.3, 4.4, 5.5, 6.6, 7.7 }; 22 char c[ cCount ] = "HELLO"; // 6th position for null 23 24 cout << "Array a contains:" << endl; 25 printArray( a, aCount ); // integer template function 26 27 cout << "Array b contains:" << endl; 28 printArray( b, bCount ); // double template function 29 30 cout << "Array c contains:" << endl; 31 printArray( c, cCount ); // character template function 32 33 return 0; 34 } Notice how type parameter T is used in place of int, float, etc. . Each type array gets operated on by a different template function. H. Artail Program Output Array a contains: 1 2 3 4 5 Array b contains: 1.1 2.2 3.3 4.4 5.5 6.6 7.7 Array c contains: H E L L O H. Artail 12.4 Class Templates • class templates – allow type-specific versions of generic classes • Format: template <class T> class ClassName{ definition } – Need not use "T", any identifier will work – To create an object of the class, type ClassName < type > myObject; Example: Stack< double > doubleStack; H. Artail 12.4 Class Templates (II) • Template class functions – declared normally, but preceded by template<class T> • generic data in class listed as type T – binary scope resolution operator used – Template class function definition: template<class T> MyClass< T >::MyClass(int size) { myArray = new T[size]; } • constructor definition - creates an array of type T H. Artail 1 // Fig. 12.3: tstack1.h 2 // Class template Stack 3 #ifndef TSTACK1_H 4 #define TSTACK1_H 5 6 template< class T > 7 class Stack { 8 public: 9 Stack( int = 10 ); // default constructor (stack size 10) 10 ~Stack() { delete [] stackPtr; } // destructor 11 bool push( const T& ); // push an element onto the stack 12 bool pop( T& ); // pop an element off the stack 13 private: 14 int size; // # of elements in the stack 15 int top; // location of the top element 16 T *stackPtr; // pointer to the stack 17 18 bool isEmpty() const { return top == -1; } // utility 19 bool isFull() const { return top == size - 1; } // functions 20 }; 21 22 // Constructor with default size 10 23 template< class T > 24 Stack< T >::Stack( int s ) 25 { 26 size = s > 0 ? s : 10; 27 top = -1; // Stack is initially empty 28 stackPtr = new T[ size ]; // allocate space for elements 29 } Notice how a member function of the class template is defined H. Artail 30 31 // Push an element onto the stack 32 // return 1 if successful, 0 otherwise 33 template< class T > 34 bool Stack< T >::push( const T &pushValue ) 35 { 36 if ( !isFull() ) { 37 stackPtr[ ++top ] = pushValue; // place item in Stack 38 return true; // push successful 39 } 40 return false; // push unsuccessful 41 } 42 43 // Pop an element off the stack 44 template< class T > 45 bool Stack< T >::pop( T &popValue ) 46 { 47 if ( !isEmpty() ) { 48 popValue = stackPtr[ top-- ]; // remove item from Stack 49 return true; // pop successful 50 } 51 return false; // pop unsuccessful 52 } 53 54 #endif Test if the stack is full. If not, push element. Test if the stack is empty. If not, pop an element. H. Artail 55 // Fig. 12.3: fig12_03.cpp 56 // Test driver for Stack template 57 #include <iostream> 58 59 using std::cout; 60 using std::cin; 61 using std::endl; 62 63 #include "tstack1.h" 64 65 int main() 66 { 67 Stack< double > doubleStack( 5 ); 68 double f = 1.1; 69 cout << "Pushing elements onto doubleStack\n"; 70 71 while ( doubleStack.push( f ) ) { // success true returned 72 cout << f << ' '; 73 f += 1.1; 74 } 75 76 cout << "\nStack is full. Cannot push " << f 77 << "\n\nPopping elements from doubleStack\n"; 78 79 while ( doubleStack.pop( f ) ) // success true returned Pushing elements onto doubleStack 1.1 2.2 3.3 4.4 5.5 Stack is full. Cannot push 6.6 Popping elements from doubleStack H. Artail 80 cout << f << ' '; 81 82 cout << "\nStack is empty. Cannot pop\n"; 83 84 Stack< int > intStack; 85 int i = 1; 86 cout << "\nPushing elements onto intStack\n"; 87 88 while ( intStack.push( i ) ) { // success true returned 89 cout << i << ' '; 90 ++i; 91 } 92 93 cout << "\nStack is full. Cannot push " << i 94 << "\n\nPopping elements from intStack\n"; 95 96 while ( intStack.pop( i ) ) // success true returned 97 cout << i << ' '; 98 99 cout << "\nStack is empty. Cannot pop\n"; 100 return 0; 101} 5.5 4.4 3.3 2.2 1.1 Stack is empty. Cannot pop Pushing elements onto intStack Popping elements from intStack 1 2 3 4 5 6 7 8 9 10 Stack is full. Cannot push 11 10 9 8 7 6 5 4 3 2 1 Stack is empty. Cannot pop H. Artail Program Output Pushing elements onto doubleStack 1.1 2.2 3.3 4.4 5.5 Stack is full. Cannot push 6.6 Popping elements from doubleStack 5.5 4.4 3.3 2.2 1.1 Stack is empty. Cannot pop Pushing elements onto intStack 1 2 3 4 5 6 7 8 9 10 Stack is full. Cannot push 11 Popping elements from intStack 10 9 8 7 6 5 4 3 2 1 Stack is empty. Cannot pop H. Artail 12.6 Templates and Inheritance • A class template can be derived from a template class • A class template can be derived from a non- template class • A template class can be derived from a class template • A non-template class can be derived from a class template H. Artail 12.7 Templates and friends • friendships allowed between a class template and – global function – member function of another class – entire class • friend functions – inside definition of class template X: – friend void f1(); • f1() a friend of all template classes – friend void f2( X< T > & ); • f2( X< int > & ) is a friend of X< int > only. The same applies for float, double, etc. – friend void A::f3(); • member function f3 of class A is a friend of all template classes H. Artail 12.7 Templates and friends (II) – friend void C< T >::f4( X< T > & ); • C<float>::f4( X< float> & ) is a friend of class X<float> only • friend classes – friend class Y; • every member function of Y a friend with every template class made from X – friend class Z<T>; • class Z<float> a friend of class X<float>, etc. H. Artail 12.8 Templates and static Members • non-template class – static data members shared between all objects • template classes – each class (int, float, etc.) has its own copy of static data members – static variables initialized at file scope – each template class gets its own copy of static member functions