the stl

Introduction Iterators Function Objects Summary References

THE STL

Muhammad Adil Raja

Roaming Researchers, Inc.

cbna

April 22, 2015

The STL Roaming Researchers, Inc. cbna


OUTLINE I

INTRODUCTION

ITERATORS

FUNCTION OBJECTS

SUMMARY

REFERENCES



INTRODUCTION

I The STL is a rich collection of standard data structures,recently added to C++.

I Will elevate data structures to the level of, say, the I/Ostream package (i.e., something taken for granted).

I In many ways, is an anti-object-oriented design, yet it ispowerful and it works.



GENERIC ALGORITHMS VS ENCAPSULATION

I Object-Oriented programming holds encapsulation as anideal, bundling all actions in one place.

I Can make for “fat” classes.I The STL separates data structures and algorithms.I The data structures are relatively small. The algorithms are

many. Can be mixed and matched.I Allows for a much smaller class library.



ITERATORS

I Basic problem – how do you allow access to elements ofcollection, without knowing how the collection isorganized?

I Solution, define a new data type specifically for creatingloops.

I A large number of algorithms are provided by the standardlibrary, all built using iterators.



DESCRIBING A RANGE OF VALUES

I Notice how a range of values is often described by astarting value and a past-the-end value.

I The past the end value is not part of the collection, but justa marker.

FIGURE : A Range of Values


http://web.engr.oregonstate.edu/~budd/Books/oopintro3e/info/slides/chap03/slide21a.gif


BEGIN AND END

I By convention, containers return a starting value inresponse to begin(), and a past-the-end value in responseto end().

I For example, to shuffle a vector of values:

BEGIN AND END

random_shuff le( aVector . begin ( ) , aVector . end ( ) , randomInteger ) ;



WHAT MUST ITERATORS DO?I To see what iterators must do, consider a typical algorithm:

EXAMPLE

template <class T>i t e r a t o r f i n d

( i t e r a t o r f i r s t , i t e r a t o r l a s t , T & value ){

while ( f i r s t != l a s t && ∗ f i r s t != value ) ++ f i r s t ;return f i r s t ;

}

Could be used to find values in an array, or in a list:

EXAMPLE

i n t data [ 1 0 0 ] ;. . .

i n t ∗ where = f i n d ( data , data +100 , 7 ) ;l i s t < int > : : i t e r a t o r where = f i n d ( a L i s t . begin ( ) , a L i s t . end ( ) , 7 ) ;



ITERATORS OPERATIONS

I An iterator can be compared for equality to another iterator.I They are equal when they point to the same position, and

are otherwise not equal.I An iterator can be dereferenced using the * operator, to

obtain the value being denoted by the iterator.I Depending upon the type of iterator and variety of

underlying container, this value can also sometimes beused as the target of an assignment in order to change thevalue being held by the container.

I An iterator can be incremented, so that it refers to the nextelement in sequence, using the operator ++.

I What makes iterators possible is that all of these can beoverloaded.



FUNCTION OBJECTS

I In C++ even the function call operator (parenthesisoperator) can be overloaded.

I Allows for creation of objects that can be used likefunctions.

EXAMPLE

class biggerThanThree {public :

bool operator ( ) ( i n t v ){ return v > 3; }

} ;

Can be used to find the first value bigger than 3, for example.



WHY DO THIS?

Objects can take arguments computed at run-time, specializefunctions in a way that simple functions cannot:

EXAMPLE

class biggerThan {public :

biggerThan ( i n t x ) : tes tVa lue ( x ) { }const i n t tes tVa lue ;bool operator ( ) ( i n t va l )

{ return va l > tes tVa lue ; }} ;

l i s t < int > : : i t e r a t o r f i r s t B i g =f i n d _ i f ( a L i s t . begin ( ) , a L i s t . end ( ) , biggerThan ( 1 2 ) ) ;

In functional languages, this kind of object is sometimes knownas a curry.



EXAMPLE PROGRAM – INVENTORY SYSTEM

A business, WorldWideWidgetWorks, manufactures widgets.

EXAMPLE

class Widget {public :

/ / cons t ruc to rsWidget ( ) : id_number ( 0 ) { }Widget ( i n t a ) : i d ( a ) { }

/ / opera t ionsi n t i d ( ) { return id_number ; }void operator = ( Widget & rhs )

{ id_number = rhs . id_number ; }bool operator == ( Widget & rhs )

{ id_number == rhs . id_number ; }bool operator < ( Widget & rhs )

{ id_number < rhs . id_number ; }protected :

i n t id_number ; / / widget i d e n t i f i c a t i o n number} ;



INVENTORY

I Inventory is two lists - items on hand, items on back order.

EXAMPLE

class i n ven to ry {public :

/ / process order f o r widget type widvoid order ( i n t wid ) ;

/ / rece ive widget o f type wid/ / i n shipment

void rece ive ( i n t wid ) ;

protected :l i s t <Widget> on_hand ;l i s t < int > on_order ;

} ;



ITEM ARRIVES IN SHIPMENT

EXAMPLE

void i n ven to ry : : rece ive ( i n t wid )/ / process a widget rece ived i n shipment

{ cout << " Received shipment o f widget type " << wid << endl ;

l i s t < int > : : i t e r a t o r we_need =f i n d ( on_order . begin ( ) , on_order . end ( ) , wid ) ;

i f ( we_need != on_order . end ( ) ) {cout << " Ship " << Widget ( wid ) << " to f i l l back order " << endl ;on_order . erase ( we_need ) ;}

elseon_hand . push_f ront ( Widget ( wid ) ) ;

}



ITEM ARRIVES ON ORDER

EXAMPLE

void i n ven to ry : : order ( i n t wid )/ / process an order f o r a widget w i th given i d number

{ cout << " Received order f o r widget type " << wid << endl ;

l i s t <Widget > : : i t e r a t o r we_have =f i n d _ i f ( on_hand . begin ( ) , on_hand . end ( ) , WidgetTester ( wid ) ) ;

i f ( we_have != on_hand . end ( ) ) {cout << " Ship " << ∗wehave << endl ;on_hand . erase ( we_have ) ;}

else {cout << " Back order widget o f type " << wid << endl ;on_order . push_f ront ( wid ) ;}

}



FUNCTION OBJECTS

I Created like an instance of a class, works like a function.

EXAMPLE

class WidgetTester {public :

WidgetTester ( i n t i d ) : t e s t _ i d ( i d ) { }i n t t e s t _ i d ;

/ / de f ine the f u n c t i o n c a l l opera torbool operator ( ) ( Widget & wid )

{ return wid . i d ( ) == t e s t _ i d ; }} ;



MAPS, INDEXED DATA STRUCTURES

MAPS

typedef map< s t r i n g , int > s t r i n g V e c t o r ;typedef map< s t r i n g , s t r i ngVec to r > graph ;

s t r i n g pendleton ( " Pendleton " ) ;s t r i n g pensacola ( " Pensacola " ) ;s t r i n g peor ia ( " Peor ia " ) ;s t r i n g phoenix ( " Phoenix " ) ;s t r i n g p i e r r e ( " P ie r re " ) ;s t r i n g p i t t s b u r g h ( " P i t t sbu rgh " ) ;s t r i n g pr ince ton ( " Pr inceton " ) ;s t r i n g pueblo ( " Pueblo " ) ;

graph cityMap ;

ci tyMap [ pendleton ] [ phoenix ] = 4 ;ci tyMap [ pendleton ] [ pueblo ] = 8 ;ci tyMap [ pensacola ] [ phoenix ] = 5 ;ci tyMap [ peor ia ] [ p i t t s b u r g h ] = 5 ;ci tyMap [ peor ia ] [ pueblo ] = 3 ;ci tyMap [ phoenix ] [ peor ia ] = 4 ;ci tyMap [ phoenix ] [ p i t t s b u r g h ] = 10;ci tyMap [ phoenix ] [ pueblo ] = 3 ;ci tyMap [ p i e r r e ] [ pendleton ] = 2 ;ci tyMap [ p i t t s b u r g h ] [ pensacola ] = 4 ;ci tyMap [ p r ince ton ] [ p i t t s b u r g h ] = 2 ;ci tyMap [ pueblo ] [ p i e r r e ] = 3 ;The STL Roaming Researchers, Inc. cbna


THE GRAPH BEING REPRESENTED

FIGURE : Graph.


http://web.engr.oregonstate.edu/~budd/Books/oopintro3e/info/slides/chap03/slide21a.gif


REPRESENTING A DISTANCE

EXAMPLE

struct Dis tancePai r {unsigned i n t f i r s t ;s t r i n g second ;Dis tancePai r ( ) : f i r s t ( 0 ) { }D is tancePai r ( unsigned i n t f , s t r i n g & s )

: f i r s t ( f ) , second ( s ) { }} ;

bool operator < ( Dis tancePai r & lhs , D is tancePai r & rhs ){ return l hs . f i r s t < rhs . f i r s t ; }



SHORTEST PATH ALGORITHM

EXAMPLE

void shor tes tD is tance ( const graph & cityMap ,const s t r i n g & s t a r t , s t r i n g V e c t o r & d is tances )

{/ / process a p r i o r i t y queue of d is tances to c i t i e spr io r i t y_queue <DistancePair , vector <DistancePair > ,

greater <DistancePai r > > que ;que . push ( Dis tancePai r (0 , s t a r t ) ) ;

while ( ! que . empty ( ) ) {/ / p u l l nearest c i t y from queue

i n t d is tance = que . top ( ) . f i r s t ;s t r i n g c i t y = que . top ( ) . second ;que . pop ( ) ;

/ / i f we haven ’ t seen i t a l ready , process i ti f (0 == d is tances . count ( c i t y ) ) {

/ / then add i t to sho r t es t d is tance mapd is tances [ c i t y ] = d is tance ;

/ / and put values i n t o queues t r i n g V e c t o r : : i t e r a t o r s t a r t , stop ;s t a r t = cityMap [ c i t y ] . begin ( ) ;stop = cityMap [ c i t y ] . end ( ) ;for ( ; s t a r t != stop ; ++ s t a r t )

que . push ( Dis tancePai r ( d is tance + (∗ s t a r t ) . second ,(∗ s t a r t ) . f i r s t ) ) ;

}}

}The STL Roaming Researchers, Inc. cbna


SUMMARY

I The Future of OOP.I Given that the STL is not OO, does this mean that OOP is

dead?I No, only that inspiration can come from a number of

sources, and not all problems are best solved in an OOPfashion.

I However, many problems ARE best approached in anOOP manner.

I Bottom line - know as much as you can about as manystyles of programming as you can, and use the style mostappropriate to the problem.



REFERENCES

I Images and content for developing these slides have beentaken from the follwoing book with the permission of theauthor.

I An Introduction to Object Oriented Programming, TimothyBudd.

I This presentation is developed with Beamer:I Szeged, beetle.


http://web.engr.oregonstate.edu/~budd/Books/oopintro3e/info/ReadMe.html

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