Object Oriented Programming Elhanan Borenstein Lecture #11 copyrights © Elhanan Borenstein

Agenda STL  General Containers  Iterators  Object Functions  STL Examples copyrights © Elhanan Borenstein

General Algorithms, Containers and Iterators copyrights © Elhanan Borenstein

Template Functions / Classes Reminder copyrights © Elhanan Borenstein template 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 iArray(10); Array fArray(10); iArray.Print(); fArray.Print(); } template 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. copyrights © Elhanan Borenstein template 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? copyrights © Elhanan Borenstein template 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 copyrights © Elhanan Borenstein  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 copyrights © Elhanan Borenstein data Class item Class T data / / / / Class list head tail Class list ::iterator Example: link_list

General Containers and Iterators A list class that can store a link list of any data type  list  …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, Array, …  list, list, list  Tree, Tree, Tree  … and many more… So, what do we have so far? copyrights © Elhanan Borenstein

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? copyrights © Elhanan Borenstein

Object Functions copyrights © Elhanan Borenstein

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 copyrights © Elhanan Borenstein

Object Functions copyrights © Elhanan Borenstein struct Sqr { template void operator() (T& number) const { t = t*t; } }; struct Print { template 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 copyrights © Elhanan Borenstein struct Reverse { template 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 copyrights © Elhanan Borenstein Putting is all together… example: apply and now…

STL copyrights © Elhanan Borenstein

STL copyrights © Elhanan Borenstein 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 copyrights © Elhanan Borenstein 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 copyrights © Elhanan Borenstein All algorithms appear in the header file 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 copyrights © Elhanan Borenstein 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 { } Numbers List { } Numbers Deque (merged) { }

Questions? copyrights © Elhanan Borenstein