C++ Programming Basics III

Transcription

1 C++ Programming Basics III Xianyi Zeng Department of Mathematical Sciences The University of Texas at El Paso. October 19, 2017.

2 C++ Programming Basics: Part II Typecasting and Class Inheritance C++ allows typecasting between base and child classes. Example: Consider the following objects: class Geometry {}; class Circle: public Geometry {}; class Square: public Geometry {}; Object slicing: Assign a child object to a base one by invoking the latter s assignment operator/copy constructor. Circle circ; Geometry geom = circ; Pointers to the base class can be used to designate a child class: Geometry* ptr geom1 = ˆ Geometry* ptr geom2 = new Square;

3 C++ Programming Basics: Part II The virtual Methods How do we get access to a child object s function by using a base pointer? Use the virtual keyword to achieve the runtime polymorphism. class Geometry {... }; virtual void calcarea(); Which calcarea to call will be determined at runtime! Circle circ; Geometry* ptr geom = ˆ ptr geom->calcarea(); // Will call Circle s calcarea() Inside the base class, one can use this (a keyword) to identify the actual pointer at runtime. See the example.

4 C++ Programming Basics: Part II The virtual Methods (Continue) Constructors cannot be virtual. From a design point of view: virtual indicates we want to perform some action with incomplete information. By constructing, however, we expect to know the complete information. Destructors, however, can be virtual: To avoid memory leak! Abstract Classes One can use virtual functions to declare an abstract class: An object that cannot be instantiated. This is achieved by making a virtual method pure virtual. example the class Geometry can be made abstract by: virtual void calcarea() = 0; which will forbid one to declare: Geometry geom; For

5 C++ Programming Basics: Part II The virtual Inheritance The diamond problem : class Geometry; class Polygon : public Geometry; class Convex : public Geometry; class Triangle : public Polygon, public Convex; Triangle will have two versions of variables/methods from the Geometry. In order to avoid ambiguity one can use, for example: tria.polygon::area; To avoid this duplication, one uses virtual inheritance: class Polygon : public virtual Geometry; class Convex : public virtual Geometry; Can be used to delegate methods.

6 Data Structure and The Standard Template Library An Introduction to Data Structures Data structures are used to manage a collection of objects of the same data type. Some basic data structures: List: An ordered sequence of data. Array: A collection of data, each selected by one or more indices. Stack: Last in, first out (LIFO). Queue: First in, first out (FIFO). Example 1: In a restaurant, one uses the disk that is lastly washed (on the top of the stack), this is a stack structure. But the customers are first-come, first-served; this is a queue structure. Example 2: Traversing a tree data structure. We tend to use stack for depth-first walk; and we use queue for breath-first walk.

7 Data Structure and The Standard Template Library An Introduction to Data Structures Some basic operations: Traversing: Visit each element one by one. Searching: Traverse until hit. Insertion: Add an element. Deletion: Delete an element. Sorting: Rearrange the order of the elements. Merging: Combine two data structures. Examples: Linked list is good at insertion/deletion, but not random access. Array is good at random access, but involve more data movement when insertion/deletion. Stack and quene are not friendly to almost all operations listed above at all, but they re extremely efficient for specific jobs.

8 Data Structure and The Standard Template Library The Standard Template Library (STL) The STL uses templates to achieve a ready-made set of common classes as containers for built-in type or user-defined objects. Major components: container, iterator, algorithm, etc. The container is an object to store data, for example: std::vector<int> array int; std::vector<geometry*> array geom; std::pair<std::string,geometry*> pair geom; std::map<std::string,geometry*> map geom; std::map<int,std::vector<double>> map double; An iterator allows the user the traverse a container: for ( std::vector<int>::iterator it = array int.begin(); it!= array int.end(); it++ ) {}

9 Data Structure and The Standard Template Library The Standard Template Library (STL) Example: Using book title to access books. std::map<std::string,book> books; books.insert( std::pair<std::string,book>("got",book("got","rrmartin")) ); books.insert( std::pair<std::string,book>("hp",book("hp","jkrowling")) ); int bct = 0; for ( std::map<std::string,book>::iterator it = books.begin(); it!= books.end(); it++, bct++ ) { Book& abook = it->second; abook.printinfo(); } assert( bct == books.size() );

10 Data Structure and The Standard Template Library The Standard Template Library (STL) The algorithm part of STL includes basic operations such as sorting and searching. std::find can be used to search for value in an std::vector. std::map has a find method to search for a certain key. std::sort can be used to sort a certain range in an std::vector. std::map is automatically sorted by the keys. The STL has much more containers/algorithms to offer: