Week 10b - Final Help with Projects

Synopsis:

Glossary of Terms

1. Projects:

   • Sample Project #1
     Lexical scanner
   • Sample Project #2
     Rule-based parser - uses templates for ScopeStack
   • Sample Project #3
     Parser with Abstract Syntax Tree - uses templates for AST
   • Sample Project #4
     Code Analyzer - uses templates to enable functions to accept callable objects of a variety of types - function pointers, functors, and lambdas

2. Course Take-aways:

   The most important things we covered in this course are:

   Summary of CSE687-OnLine - Object Oriented Design

   1. C++ Language
      A large, but elegant, programming language that compiles to native code. It favors enabling users over protecting them.

      • Historical Context
        C++ derives most of its language elements and function structure from the C programming language, which in turn, inherited those things from Algol, a European language. It derives its notions of class from SmallTalk.
      • Classes
        A class is a language construct that binds together member functions and data, providing access to users only to public member functions, not to its data. This encapsulation enables the class to make strong guarantees about validity of its data.
      • Rule of Threes
        For each of your classes, always consciously choose between providing construction, assignment, and destruction operations, allowing the compiler to generate them, or disable them.
      • Abstract Data Types
        An abstract data type is simply a value type, e.g., it provides copying, assignment, and move operations that allow instances of the type to behave like built-in types.
      • Templates
        Templates are compile time constructs that allow us to avoid writing a lot of nearly identical code for classes that could sensibly use any of several concrete types, perhaps as arguments to member functions or as instances of member data. Containers are a good example.

        Templates are also useful for building functions that accept callable objects, i.e., function pointers, functors, or lambdas. We use template functions to accept instances of any of these distinct types. Thread constructors are a good example.

        Here are a few interesting examples of template use:

        • Defining C++ properties using templates
        • Graph class representing networks of nodes connected with arcs
        • Demonstration of several ways to traverse m-ary tree structures

        There are many more linked in the Templates lecture page.
      • Functors
        A functor is a class that defines operator(). That means that instances can be "invoked" like this:

          class AFunctor {
          public:
            AFunctor(const X& x) : x_(x) {}
            void operator()(const Y& y) { /* do something useful to x_, using y */ }
            X value() { return x_; }
          private:
            X x_;
          };
        
          AFunctor func;
          Y y;
          func(y);          // syntactically looks like a function call
          func.operator(y); // equivalent to the statement above
                              

      • lambdas
        A lambda is an anonymous callable object that can be passed to, and returned from other functions. A lambda is really a short-cut to define a functor. A very useful feature of lambdas is their capture semantics. They can store data defined in their local scope, to be used later when they are invoked.
      • Callable Objects
        A callable object is any C++ construct that can be invoked using parentheses, callable(...). Function pointers, functors, and lambdas are all callable objects.
      • Class Relationships
        Classes have four relationships:

        • Inheritance:

          A derived class inherits all it's base's members. Non-virtual base functions should not be redefined in the derived class. Virtual member functions may be redefined in the derived class. Pure virtual functions must be redefined.

        • Composition:

          Instances declared as class data members are composed by the class, creating a strong owning relationship. Composed members are always constructed when the composer is constructed, and destroyed when the composer is destroyed.

        • Aggregation:

          A class aggregates a data member when it holds a pointer to the member instance on the native heap. Creation of an instance of some type as local data in a member function is also considered to be aggregation. Aggregated instances are owned by the aggregator, but this is a weaker relationship than composition, as the aggregated instances do not exist until code in the aggregator creates them.

        • Using:

          A class uses an instance of some other class when it is passed the instance to one of its public member funtions by reference. Using is a non-owning relationship and your classes should respect the owning code by doing nothing to invalidate the used instance. Passing an instance by value to a member function is really aggregation, because the receiving class creates and uses its own copy.

        These four relationships are all that are needed to build Object Oriented programs.
      • Compound Objects
        Compound objects are instances of classes that use inheritance, composition, and aggregation of other classes to carry out their mission. We need to be careful, especially with initialization, to ensure they operate as expected. Here is a good example of the initialization and use of compound objects.
      • Exceptions
        Exceptions are a language defined mechanism for handling errors. Exception handling uses instances of std::exception and the key words throw, try, and catch. You should always throw exceptions by value and catch them by reference.
      • Namespaces
        A namespace defines a compile-time scope used to distinguish between two or more type or function names with the same value but that have distinct definitions in separate places in code for a single compilation unit. A namespace extends the name of a type, for example, by prepending the type name with the namespace name, i.e., MyNamespace::MyType.
      • Dark Corners:
        The C++ language has a surprisingly short list of dark corners, e.g., compilable constructs that may cause subtle errors. These all have to do with causing Liskov Substitution to fail by improper overloading, overriding, or failing to provide virtual destructors.

      An excellent online reference for the C++ language is the site: cppreference.com.
   2. Threads
      A block of processing instructions, defined by a function passed to the operating system (OS), that executes in a processor core, and is started and stopped by the OS. A thread often runs in an environment containing many other threads that are sequenced in short time-slices by the OS to behave like concurrent processing. A thread may run continuously in a core if there are no other threads contending for that resource.

      The C++ Standard Library provides the libraries: thread and atomic to support concurrency.
   3. Sockets
      An interface for network communication provided by a low-level library. The sockets we discuss are all stream-oriented, reading and writing sequences of bytes. Stream-oriented means that sockets do not provide you with a message structure. If you need that you will have to provide it.

      In order to communicate these sockets have to be connected. To connect, your code needs, on one end of the channel, a connecter socket and, on the other end, a socket listener, to listen for, and establish a connected channel.

      You will find that the Sockets library, in our repository, provides good support for building programs using network communication.
   4. Graphical User Interfaces
      The standard C++ libraries do not provide any support for Graphical User Interfaces. But it is fairly easy to provide one for a native C++ application by using a C#-based Windows Presentation Foundation (WPF) project that communicates with the application through a C++\CLI shim. The WPF-Interop demo is a simple example of how to do this.

      • WPF

        A Graphical User Interface (GUI) framework that:
        • Builds interface windows using a custom XML markup, called XAML, and C# or C++\CLI event handlers.
        • Layout model is similar to HTML.
        • Provides pervasive dependency relationships between graphical elements and bubbling of events.
        • Supports very complete designer control over the appearance and behavior of each window view.
        • Runs only on Windows, as a desktop application.

      • C++\CLI

        A .Net managed language that runs in a Common Language Runtime (CLR) virtual machine and stores its instances in a managed heap, providing garbage collection, exception handling, and reflection services. C++\CLI code interoperates directly with native C++ code. C++\CLI code and native C++ may be placed in the same file.
   5. Standard Libraries
      The C++ language uses a very well engineered set of standard libraries for I/O, managing data, and using threads, and much more. Each new C++ standard introduces new libraries or new library features. We've focused on these:

      • Streams library

        A collection of libraries for stream-based I/O, for the console, files, and in-memory strings. Streams use the insertion operator<<(...) and extraction operator> >(...) to build composable input and output operations. Here is a brief presentation about the structure of the streams library. Almost all of the capabilities of the streams library are demonstrated here:
        • formatting I/O
        • reading and writing files
        • reading and writing in-memory strings
        • using filebufs to stream data
        • reading and writing to the same filebuf

      • STL library

        The Standard Template Library is a subset of the C++ standard libraries. It provides a large set of containers, each with a defined iterator type, and a set of algorithms designed to operate on the containers. All of the containers are endowed with correct construction, copy, and destruction semantics. Here is a presentation of the structure and top-level properties of the STL.

      • Threads library

        The Threads library, introduced in the C++11 standardization, contains classes for threads, locks of various kinds, atomics, condition variables, and futures. Futures are interesting because they support returning values computed by child threads, blocking until the result is ready. Here are some useful code demos and resources for programs that use threads:
        • Blocking Queue
        • C++11 Concurrency demos
        • Techniques for doing some useful things with threads
        • Comparison of perfomance of Win32 locking with performance of C++11 locking
   6. Custom Libraries
      These libraries are code that I've written, and hosted on the college server. They supplement the C++ Standard Libraries, providing functionality that does not exist there (as of C++11).

      • FileSystem

        A library for managing and queriny Windows directories and their objects. It was written entirely in C++11, using the Win32 API. It has classes File, FileInfo, Directory, and Path, that are modeled after the very well-engineered .Net System.IO library.

      • Sockets

        A library that provides an abstraction above the Windows sockets library, making many of its operations more user friendly. It provides classes: Socket, SocketConnecter, SocketListener, and SocketSystem.

      • C++ Properties

        .Net and Java properties provide simple access to class data, without compromising encapsulation. This is a small library designed to provide equivalent functionality. It useful, but also interesting because it illustrates that the C++ language can easily be extended using only features of C++.

      • XmlDocument

        A library for constructing XML strings and files, and creating a Document Object Model (DOM) instance from well formed XML strings and files.

   I trust you will find this synopsis of the CSE687-Online Course useful as you take the course, and as reference material for later courses, and for interviews and professional work.