Templates C++

7/30/2019 Templates C++

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Templates(using C++)


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Introduction

Templates are part of ANSI C++ Standard.

Template is a technique that allows using a single

function or class to work with different data types.

A single function is created to process any type of data

with in template.

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Introductioncontd.

The template provides generic programming by defining

generic classes.

In Templates, generic data types are used as arguments and

they can handle a variety of data types.

A function that works for all C++ Data types is called a

generic function.

The formal arguments of template functions are of

template(generic) type.

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Types of Templates

FunctionTemplates

Class

Templates


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C++ Function Templates

Approaches for functions that implement identical

tasks for different data types

Nave Approach

Function Overloading Function Template

Instantiating a Function Templates


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Approach 1: Nave Approach

create unique functions with uniquenames for each combination of data

types difficult to keeping track of multiple

function names

lead to programming errors


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Examplevoid PrintInt( int n )

{ cout


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Approach 2:Function Overloading

(Review) The use of the same name for different C++

functions, distinguished from each other bytheir parameter lists

Eliminates need to come up with many different names foridentical tasks.

Reduces the chance of unexpected results caused byusing the wrong function name.


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Example of Function Overloading

voidPrint( int n ){

cout


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Approach 3: Function Template

A C++ language construct that allows the compiler to generatemultiple versions of a function by allowing parameterized data types.

Template < TemplateParamList >FunctionDefinition

FunctionTemplate

TemplateParamDeclaration: placeholder

class typeIdentifiertypename variableIdentifier


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1. The first statement tells the compiler that the following function or class

declaration can use the template data type.

2. Templates can not be declared inside classes or functions.

3. They must be global and should not be local.

Template //Template declaration

Class cname

{// data members and member functions

}


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Example of a Function Template

template

void Print( SomeType val ){

cout


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Instantiating a Function Template

When the compiler instantiates a template,it substitutes the template argument for thetemplate parameter throughout the functiontemplate.

Function < TemplateArgList > (FunctionArgList)

TemplateFunction Call


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Summary of Three Approaches

Nave ApproachDifferent Function Definitions

Different Function Names

Function OverloadingDifferent Function Definitions

Same Function Name

Template Functions

One Function Definition (a function template)Compiler Generates Individual Functions


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#include

#include

template

void show(SS tv)

{

cout


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Class Template

A C++ language construct that allows the compiler to generatemultiple versions of a class by allowing parameterized data types.

Template < TemplateParamList >ClassDefinition

Class Template

TemplateParamDeclaration: placeholder

class typeIdentifiertypename variableIdentifier


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Instantiating a Class Template

Class template arguments mustbe explicit.

The compiler generates distinct class typescalled template classes or generated classes.

When instantiating a template, a compilersubstitutes the template argument for thetemplate parameter throughout the class

template.


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#include

#include

template

class demo

{

public:

demo(T tvar, T1 tv)

{

cout

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Templates C++