Object Oriented Programming Elhanan Borenstein [email protected] Lecture #11 copyrights © Elhanan...

Object OrientedProgramming

Elhanan Borenstein

[email protected]

Lecture #11

copyrights © Elhanan Borenstein

Agenda STL

General Containers

Iterators

Object Functions

STL Examples


General Algorithms, Containers and Iterators


Template Functions / ClassesReminder


template<class T> void Swap(T& a, T& b) { T temp = a; a = b; b = temp;}

void main(){ int i=4, j=9; Swap(i, j);

char* str1 = “hello”; char* str2 = “world”; Swap(str1, str2);

Array<int> iArray(10); Array<float> fArray(10);

iArray.Print(); fArray.Print();}

template<class T> class Array{ T* arr; int size;public: Array(int s) : size(s), arr(new T[size]) {}

T& operator[](int index) {return arr[index];}};

A General Find Function Let’s recall the general Find function we saw in the last lecture:

Implement a generic Find() function, which gets: a pointer to the beginning of an array a pointer to the end of an array the value to search for

The function returns the address of the first items in the array that is equal to the given value or the address of one location after the last item if the value was not found.


template<class T>T* Find(T* begin, T* end, T value){ while (begin != end && *begin != value)

begin++;

return begin;}

void main(){ int array[ ] = {3,2,5,7,2,8,11}; int size=sizeof(array)/sizeof(array[0]); int* found; found = Find (&array[0], &array[size], 7); if (found != &array[size])

cout<<“FOUND!!!”<<endl;} Can Find() work on a linked-list?

A General Find Function Now let’s enhance this function:

What restrictions does Find pose on the parameters? Why do we use two types in the template? Can Find() work on other data structure other than arrays?


template<class iterator, class T>iterator Find(iterator begin, iterator end, const T& value){ while (begin != end && *begin != value)

begin++;

return begin;}

void main(){ int array[ ] = {3,2,5,7,2,8,11}; int size=sizeof(array)/sizeof(array[0]);

int* found; found = Find (&array[0], &array[size],7); if (found != &array[size])

cout<<“FOUND!!!”<<endl;}

Iterators

It appears that Find() can still work only on arrays, as we are using begin++ to iterate the items.

BUT… suppose our data-structure implanted an additional iterator class. This

class will support the followings:

Introduction & Concepts


Represent an object that can “point” to an item in our data structure. Overload the operator *, so that using *iter will return the item. Overload the operator ++ by moving to point on the next item. Overload the operator ==/!= to compare whether two Iterators points

to the same item. Overload the casting operator to allow casting to item*.

The iterator class, “behaves” just like a pointer to data item (item*), although it is actually a completely separate class.

Link List Example


data

Class item<T>

Class T

data data data

/

///

Class list<T>

head tail

Class list<T>::iterator

Example: link_list

General Containers and Iterators

A list<T> class that can store a link list of any data type list<int> list<float> list<Employee> …and many more…

A general Find() function that can find an item in any data structure (providing an iterator implementation) holding any data type Array<int>, Array<float>, … list<int>, list<float>, list<Employee> Tree<int>, Tree<Employee>, Tree<string> … and many more…

So, what do we have so far?


Object Functions

Let’s try to use the same mechanism to send the entire data structure to a template function – Apply() which will perform a certain operation/transformation on all the items of the DS

Again, we wish that: Apply() will work with any data structure (implementing iterators). The data structure can store any data type. Apply() will support any operation we wish !!!

What’s Next?


Object Functions


Object Functions

Our Apply() function will get: begin iterator end iterator operation.

In C, when we wanted to send an “operation” as a parameter, we used a function pointer.

In C++, we will naturally, use an Object.

Introduction


Object Functions


struct Sqr{ template<class T> void operator() (T& number) const {

t = t*t; }};

struct Print{ template<class T> void operator() (const T& printalbe) const {

cout<<printable<<endl; }};

#include “sqr.h”#include “print.h”

void main(){ Sqr MySqrMachine; Print MyPrintMachine;

int i = 2; float f = 3.25; Employee em(“John”, 3000);

MySqrMachine(i); MySqrMachine(f); MyPrintMachine(i); MyPrintMachine(em);}

sqr.h

print.h

main.cpp

Object Functions


struct Reverse{ template<class T> void operator() (T& reversable) const {

reverse(reversable.begin(), reversable.end()); }};

Struct is used, as the entire class is public. Note the format of the operator “()” What restrictions are posed on the parameters send to these object functions?

Guidelines

void main(){ string str = “dlrow olleH”; Reverse rev;

rev(str);}

Object Functions


Putting is all together… example: apply

and now…

STL


STL


The classes, and algorithms we saw in the previous slides are actually a simulation of the way STL classes, containers and algorithms work. … and now for a brief overview of what STL really includes. In general STL includes the following components:

Data Structures – (vector, list, set, …) Generic Algorithms – (for each, find, sort, …) Object Functions Allocators

Introduction

STL


STL provides the following data structures: vector – dynamic array (supporting resizing) deque – a queue or a stack list – doubly linked list map – Hashtable (key, value pairs) multimap – Hashtable, supports numerous values stored with each key set – Hashtable, storing keys only. Each key can only be stored once multiset – Hashtable, storing keys only. Each key can be stored several times

All DS supports: begin(), end(), insert(…), erase(…), clear(...)

Data Structures

STL


All algorithms appear in the header file <algorithm> Include: for_each (analog to our Apply()), find, find_if, count, replace, copy, sort,

reverse and many more.

Generic Algorithms

Commonly used with STL. Include: pow, sqrt, sin, other math functions, complex numbers functions, logic

functions, comparison functions and many more.

Object Functions

STL - Examples


Example : STL1.cpp

Example : STL2.cpp (merging a vector and a list)Names: {She Sells Sea Shealls by the Sea Shore }Number of names starts with S = 6

Numbers Vector { 4 7 8 10 14 16 67 123 }Numbers List { 0 1 2 3 4 5 6 7 }Numbers Deque (merged) { 0 1 2 3 4 4 5 6 7 7 8 10 14 16 67 123 }

Questions?


Object Oriented Programming Elhanan Borenstein [email protected] Lecture #11 copyrights © Elhanan...

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