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TEMPLATESTEMPLATES

Anas P.S21-Feb-2011


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DefinitionDefinition

y Templates are mechanisms for generating

functions and classes based on typeparameters

y Also called type parameterization

Types are given as parameters to a template

Like variables are given as a functions parameters

y

Two typesFunction Templates And

Class Templates


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Function TemplatesFunction Templates

Syntax:

template

function_declaration;

-Or-

template

function_declaration;


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4

Templates of Functions (Example)

// Precondition: x[] is an array of length n, of

// a generic type. n is a positive integer.

// Postcondition: the output is the minimum in x[]

template T min(T x[], int n){T m = x[0]; // M is the minimum so far

for (int i=1;i


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How to Call a Function Template

functionName(parameter-list);

int x[]={11, 13, 5, 7, 4, 10};

double y[]={4.5, 7.13, 3, 17};int minx = min(x,6);

double miny=min(y,4);

cout


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Function with two generic typesFunction with two generic types#include using namespace std;template void myfunc(type1 x, type2 y)

{cout


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Class TemplatesClass Templates

template

class ClassName{

definition

};

Syntax:

Need not use "T", any identifier will work

To create an object of the class, typeClassName< type myObject;

Example:Stack< double >doubleStack;


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Class Template(Example)Class Template(Example)

#include#include

using namespace std;templateclass Stack

{public:

Stack(){top = 0;}

~Stack(){};void push(StackT t);

void pop();

private:int top;StackT st[2];

};

templatevoidStack::push(StackT a)

{if(top>1){

cout


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Class Template(Example)Class Template(Example)

continuescontinuestemplatevoid Stack::pop(){

if((top)


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Output is:Output is:void main(){

Stack c;c.push(1);

c.push(2);c.push(3);

c.pop();c.pop();c.pop();

Stack c1;c1.push('a');c1.push('b');c1.push('c');

c1.pop();c1.pop();

c1.pop();

}

Index: 0 1Index: 1 2

Stack FullPoped Element is : 2Poped Element is : 1Nothing to pop

Index: 0 aIndex: 1 b

Stack FullPoped Element is : bPoped Element is : aNothing to pop


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Class templates ContinuesClass templates ContinuesThe declarations and definitions need to be in the same header file

//B.Htemplate class b{

public:b() ;

~b() ;} ;

// B.CPP#include "B.H"template b::b() { }

template b::~b() { }

//MAIN.CPP#include "B.H"void main(){

b bi ;b bf ;

}

This wont compileReason:-When compiling B.cpp, the compiler has both the declarations andthe definitions available. When the compiler compiles main.cpp has the

declarations but no definitions


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SolutionSolution

y The first solution is to physically move

the definition of the template functioninto the .h file,


public:b() ;

~b() ;} ;

template b::b() { }template b::~b() { }


b bi ;b bf ;

}


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Solution continuesSolution continues

y The other solution is to leave the

definition of the template function in the.cpp file and simply add the line template

template b; to that file:


public:b() ;

~b() ;} ;

// B.CPP#include "B.H"template b::b() { }

template b::~b() { }

template b;


b bi ;b bf ;

}


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STL(Standard Template Library)STL(Standard Template Library)

y The Standard Template Libraries (STL's) are a set of C++ templateclasses to provide common programming data structures and functionssuch as doubly linked lists (list), paired arrays (map), expandable arrays

(vector), large string storage and manipulation (rope), etc.

y The standard library is defined in a namespace called std and is

presented as a set of headers.y For using a particular container, you need to include the corresponding

headers in your program.

y Since the STL classes are part of the std namespace, you will need to

either prefix every container class type with "std::.#include

std::vector myIntVector; or include "using namespace std;" at the beginning of the code.#include

using namespace std;

vector myIntVector;


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Some DefinitionsSome Definitionsy The standard template library (STL) contains

Containers

Algorithms

Iterators

Containers:A container is a way that stored data is organized in memory, forexample an array of elements.

Eg: an array of elements

Algorithms: Algorithms in the STL are procedures that are applied tocontainers to process their data

Eg:search for an element in an array, or sort an array. You can reversethe order of elements in a vector

Iterators: Generalization of pointers,used to traverse the objects stored in a

containerEg: you can increment an iterator to point to the next element in an array


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y Algorithms use iterators to interact with

objects stored in containers

Algorithm

Iterator

Iterator

Algorithm

Iterator

Iterator

Algorithm


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Container TypesContainer Types

y The STL provides several basic kinds ofcontainers

: one-dimensional array

: double linked list : double-ended queue

: queue

: stack

: set : associative array


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VectorVector

y A vector is a Sequence that supports random access to elements,constant time insertion and removal of elements at the end, andlinear time insertion and removal of elements at the beginning or inthe middle.

y The number of elements in a vector may vary dynamically; memorymanagement is automatic.

y Vector is the simplest of the STL container classes, and in manycases the most efficient.

y #include


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Syntax: vectorFor example : vector - vector of integers.

vector - vector of strings.vector - vector of pointers to integers.vector - vector of pointers to

CMyClass objects.

Construction: A vector can be initialized by specifying itssize and

a prototype element or by another vector

vector

v1(1000); // creates vector of size 1000,// requires default constructor for

Vector Continues.Vector Continues.


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ExampleExample

void example(){

const int nSize = 10;vector vecEgs(nSize );

// initialize vec.vecEgs[0] = 1;int nEgArr [nSize ];

for( int nCount = 0; nCount > word;

svec.push_back(word);//ok

if (svec.at(3) == aaa) //error..exception

string strNew = svec[3]; //error..exception


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InsertionInsertion

vector vecEgspush_back

vecEgs.push_back(10);//inserts at end

InsertvecEgs.insert(vecEgs.begin() , 10) ; //inserts ata posvecEgs.insert(pos,n,10) //inserts n elementsat a posThis is equal tofor (int nCnt = 0;nCnt < n ;++ nCnt)

vecEgs.insert(pos, 10)


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DeletionDeletion

y erase erase at any position -

vecEgs.erase (pos)

Basic operations Pop_back removesone from end


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Points to notePoints to note

y Insertion at the back of a vector is efficient.y The vector simply grows, if necessary, to

accommodate the new item.y It is expensive to insert (or delete) an element in

the middle of a vector the entire portion of thevector after the insertion (or deletion) pointmust be moved, because vector elements occupycontiguous cells in memory

y It is faster to insert many elements at once than

one at a timey Use const iterators if you dont need to modify

the elements


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ListList

y Provide linear time access to asequence of varying length withconstant time insertions and

deletions at any position


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ExampleExampley #include

y #include

y #include

y #include

y using namespace std;

y void main()

y {y list li;

y li.push_back(100);


y li.push_front(90);

y list::iterator it;

y for(it=li.begin();it!=li.end();it++)

y {

y cout


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DequeDeque

y Provide random access to a sequence of

varying length with constant timeinsertions and deletions at both beginning

and the end


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ExampleExampley #include

y #include

y #include

y #include

y using namespace std;

y void main()

y {y deque li;



y li.push_front(90);

y li.pop_front();

y deque::iterator it;

y for(it=li.begin();it!=li.end();it++)

y {

y cout


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vector Deque list

Insertionand

deletion

Efficient atthe end

pos

Efficient atthe end

and start

Efficientat any

position

Random

Access

YES YES NO

iterator Deletioninvalidatespastelements

Invalidatealliterators

Invalidate onlythedeleted

one

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