CE00314-2 Further Programming Concepts in C++

CE00314-2Further Programming Concepts in C++ Lecture 6 Part 1 - Templates Part 2 - Further Inheritance

Introduction • Part 1 • Template definition • Function templates • Class templates • Part 2 • Further inheritance

Template Definition • Cambridge Dictionary • template1 a pattern made of metal, plastic or paper, which is used for making many copies of a shape or to help cut material accurately2 a system that helps you arrange information on a computer screen • C++ • Pattern for handling generic data

Function overloading • Swap revisited • To handle integersvoid swap(int& rnA, int& rnB){ int nTemp; nTemp = rnA; rnA = rnB; rnB = nTemp}

Function overloading • Swap revisited • To handle charactersvoid swap(char& rnA, char& rnB){ char nTemp; nTemp = rnA; rnA = rnB; rnB = nTemp}

Function overloading • Swap revisited • float, double ……. • Separate functions for each ?? • Generic function • Generic functionality • Generic data – automatically typed when used • Template function

Template function • Conceptuallyvoid swap(Type_of_Var& Var1, Type_of_Var& Var2){ Type_of_Var Temp; Temp = Var1; Var1 = Var2; Var2 = Temp;}

Template Function - syntax template<class T> // template prefix void swapValues(T& Var1, T& Var2) { T Temp; Temp = Var1; Var1 = Var2; Var2 = Temp; } • For demonstration see – Template1.cpp

Template functions - array print • Handling unspecified arrays • Array length?template<class T>void printArray(const T *array, constint nSize){for(int nCount = 0; nCount < nSize; nCount++) cout << array[nCount] << “ “; cout << endl;} • For usage example see – Template2.cpp

Template Functions - returning Also possible to have generic returntemplate<class T> T addValues(T Val1, T Val2) { return Val1 + Val2; } • See Template3.cpp for usage example

Template Functions – multiple types • Possible to have more than one type • template<class T1, class T2> • Must use all parameters • All must be utilised within function • See Template4.cpp • Possible to use Tx for casting and return type • See Template5.cpp

Template functions - Plenary • Produce generic solution • Data types provided at run time • Operators must be able to handle types • Overloaded operators included • Use of keyword “class” can be replaced with “typename” • ANSI/ISO standard allows • Programmers tend to use “class”

Class Templates • Syntax basically the same as when using function templates • must use keyword “class”template<class T>class Pair{private: T first; T second;private: Pair(); Pair(T Val1, T Val2); • etc….. • See Template6.cpp for further details

Class templates • So far….. • Class within main file • Could place within .h file • and include • See Template7.cpp • Shows use of Array of pointers • ? – mixed types?

Plenary – Part 1 • Concept of templates • Template functions • Use of “class” or “typename” keywords • Template classes • Must use “class” keyword • Tutorial Work • Experiment with given code • Is it possible to mix types when using arrays etc?

Part 2 – Further Inheritance • Base Class • e.g. Shape • Not viable as object • Also consider “Dog” • May prevent object instantiation • Class becomes “Abstract Base Class”

Abstract Base Class • Dummy definitions • Overridden within derived class • Virtual methods • Without any definition • “Pure Virtual Functions” • Only within ABC • Class containing ABCs • Can not be used to instantiate objects

This is meaninglessin a real sense Abstract Base Class Shape Circle Square Triangle

Abstract Base Class • May not be able to instantiate • But …… • ….. still vital to hierarchy • See Abstract1.cpp & Abstract1.h

Within “Shape” class • Could have empty methods • virtual void Draw( ) { } • Or make it pure virtual • virtual void Draw ( ) = 0; • Within Shape – no functionality for Draw( )

Tutorial Work • As for templates • Plus • Experiment with ABCs – using Abstract1.ccp & .h • Research for assignment • Next Week • Bob Hobbs

CE00314-2 Further Programming Concepts in C++