Developed By : Mrs. K. M. Sanghavi

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1 Developed By : Mrs. K. M. Sanghavi

3 Introduction Function Overloading Vs. Function Templates Function Templates Overloading Function Templates Class Templates Class Template And Non-Type Parameters Template And Inheritance

4 Template and Friends Generic Functions Applying Generic Functions Generic Classes Typename and Export Keyword Power of Templates

5 INTRODUCTION C++ templates Allow very general definitions for functions and classes Type names are parameters instead of actual types Precise definition determined at run-time

6 C++ Function Templates Approaches for functions that implement identical tasks for different data types Naïve Approach Function Overloading Function Template Instantiating a Function Templates 6

7 Approach 1: Naïve Approach Create unique functions with unique names for each combination of data types Difficult to keep track of multiple function names lead to programming errors 7

8 void PrintInt( int n ) { cout << "***Debug" << endl; cout << "Value is " << n << endl; } void PrintChar( char ch ) { cout << "***Debug" << endl; cout << "Value is " << ch << endl; } void PrintFloat( float x ) { } void PrintDouble( double d ) { } Example To output the traced values, we insert: PrintInt(sum); PrintChar(initial); PrintFloat(angle);

9 Approach 2: Function Overloading Review The use of the same name for different C++ functions, distinguished from each other by their parameter lists Eliminates the need to come up with many different names for identical tasks. Reduces the chance of unexpected results caused by using the wrong function name. 9

10 Example of Function Overloading void Print( int n ) { cout << "***Debug" << endl; cout << "Value is " << n << endl; } void Print( char ch ) { cout << "***Debug" << endl; cout << "Value is " << ch << endl; } void Print( float x ) { } To output the traced values, we insert: Print(someInt); Print(someChar); Print(someFloat);

11 Approach 3: Function Template A C++ language construct that allows the compiler to generate multiple versions of a function by allowing parameterized data types. FunctionTemplate Template < TemplateParamList > FunctionDefinition TemplateParamDeclaration: placeholder class typeidentifier typename variableidentifier 11

12 Function Template Syntax Allow swap values of any type variables: template<class T> void swapvalues(t& var1, T& var2) { T temp; temp = var1; var1 = var2; var2 = temp; } First line called template prefix Tells compiler what s coming is template And that T is a type parameter

13 Template Prefix Recall: template<class T> In this usage, class means type, or classification Can be confused with other known use of word class! C++ allows keyword typename in place of keyword class here But most use class anyway

14 Template Prefix Again: template<class T> T can be replaced by any type Predefined or user-defined (like a C++ class type) In function definition body: T used like any other type Note: can use other than T, but T is traditional usage

15 Calling a Function Template Consider following call: swapvalues(int1, int2); C++ compiler generates function definition for two int parameters using template Likewise for all other types Needn t do anything special in call Required definition automatically generated

16 Instantiating a Function Template When the compiler instantiates a template, it substitutes the template argument for the template parameter throughout the function template. TemplateFunction Call Function < TemplateArgList > (FunctionArgList) 16

17 Example of a Function Template template<class SomeType> void Print( SomeType val ) { cout << "***Debug" << endl; cout << "Value is " << val << endl; } Template parameter (class, user defined type, built-in types) Template argument To output the traced values, we insert: Print<int>(sum); Print<char>(initial); Print<float>(angle);

18 Another Function Template Declaration/prototype: template<class T> void showstuff(int stuff1, T stuff2, T stuff3); Definition: template<class T> void showstuff(int stuff1, T stuff2, T stuff3) { cout << stuff1 << endl << stuff2 << endl << stuff3 << endl; }

19 showstuff Call Consider function call: showstuff(2, 3.3, 4.4); Compiler generates function definition Replaces T with double Since second parameter is type double Displays:

20 Function Templates vs. Overloading Could overload function for char s: void swapvalues(char& var1, char& var2) { char temp; temp = var1; var1 = var2; var2 = temp; } But notice: code is nearly identical! Only difference is type used in 3 places

21 Multiple Type Parameters Can have: template<class T1, class T2> Not typical Usually only need one replaceable type Cannot have unused template parameters Each must be used in definition Error otherwise!

22 Another Template Example: passing two parameters template <class T, int size> class Stack {... T buf[size]; }; Stack<int,128> mystack; non-type parameter

23 Summary of Three Approaches Naïve Approach Different Function Definitions Different Function Names Function Overloading Different Function Definitions Same Function Name Template Functions One Function Definition (a function template) Compiler Generates Individual Functions

Introduction to C++ Templates and Exceptions. C++ Function Templates C++ Class Templates Exception and Exception Handler

Introduction to C++ Templates and Exceptions C++ Function Templates C++ Class Templates Exception and Exception Handler C++ Function Templates Approaches for functions that implement identical tasks for