Systems Programming Lecture 12: C++ Classes

Systems Programming Lecture 12: C++ Classes

• Lecture covers C++ classes, a key component of object-oriented programming.
• Summative submission points involve executable and library files, report PDFs, Makefile rules, code quality, output generation, example result visualizations, and result timing/memory profile graphs.

Key Differences Between C and C++

• C++ uses the iostream library for input/output, while C relies on separate functions.
• C++ employs cin, cout, and cerr for input/output, whereas C requires different I/O functions.
• C++ employs the << and >> operators for stream input/output.
• C++ uses namespaces, like std::, to group elements.

Dynamic Memory Allocation (new and delete)

• In C++, dynamic memory allocation is simplified compared to C.
• new allocates space on the heap, eliminating the need for size specification.
• delete frees up allocated memory.
• C uses malloc and calloc for heap allocation, and free to deallocate.

Object Classes in C++

• C++ classes contain data members (attributes) and member functions (methods).
• C++ classes, similar to Java, encapsulate data and methods that operate on it.
• C++ classes do not utilize a garbage collector, unlike Java.

Object Classes in C++ (Declaration and File Organization)

• Typically, declared in a header (.h) file.
• Member functions defined in a source (.cpp) file.
• Typical source file extensions include .cpp, .cxx, .cc, and .C.

Object Oriented Programming (OOP) in C++

• In OOP, "objects" (instances of classes) can encapsulate data and methods operating on it.
• OOP is not readily achievable with C-style structs.

C++ Class Declaration Example

• Classes, structs, and public: sections are used to create data members (e.g., width, height).
• public: members can be accessed outside the class.
• private: members cannot be accessed outside the class.

C++ Constructors

• Constructors initialize objects.
• Default constructors can be specified explicitly.
• Some examples given show initialization lists within constructors, which allow more readable constructor code and improve efficiency by using compile-time initialization rather than run-time initialization (e.g., Rectangle r(2,5)).

C++ Methods (Functions)

• Functions, also known as methods, are defined as part of a class.
• A class can define multiple methods to operate on its data (e.g., the Rectangle::Area() method for instance).

C++ Public Methods: Print()

• The Rectangle::Print() method shows how to output the class member variables (width and height).

Default Constructor and Initialization Lists

• Initialization lists initialize data members during object creation.
• The Rectangle class can utilize initialization lists for efficient and precise member variable assignment.

C++ Destructors

• Destructors clean up resources when an object is destroyed.
• Destructors are automatically invoked.
• C++ destructors are designated with a tilde (~) preceding the class name (e.g., ~Rectangle).
• Automatic variables are destroyed automatically, so a destructor may not need code, though it may still sometimes be beneficial.

Passing Variables (by Value, Pointer, Reference)

• In C++, variables can be passed to functions by value, pointer, or reference.
• Pass by value does not affect the original variable outside the function.
• Pass by pointer changes the original value because the function obtains the memory address.
• Pass by reference changes the original value because the reference is an alias for the original variable.

References vs. Pointers

• References are aliases for variables; pointers hold memory addresses.
• References cannot be NULL, while pointers can.
• References have stricter value semantics.
• Pointers have greater flexibility in memory management.

C++ const Keyword

• The const keyword designates variables as having constant values.
• Functions or variables preceded by const mean the values or behaviors of those functions/variables cannot be changed.

Function Overloading

• Function overloading in C++ permits multiple functions with identical names but distinct parameter lists—allowing functions to perform identical operations on various data types.

Operator Overloading

• Operator overloading in C++ enables you to redefine how operators, such as +, -, <<, or >>, behave for specific classes.

Friend functions

• A friend function isn't a member of a class, yet it has access to private class members.
• Friend functions are declared explicitly within a class as friends.

C++ Rules of Three/Five

• If a class defines a copy constructor, a destructor, or any of the other "copy" functionalities, it should likely define all of them.

Move Semantics

• Move semantics were introduced in C++11.
• The move constructor is typically used to transfer resources from a temporary object to a new one (e.g., when returning a locally created object from a function).
• Move Semantics are generally a good practice, ensuring objects are not unnecessarily copied in potentially expensive operations.
• Copy elision (or return value optimization) is a useful optimization that often eliminates the need for explicit move constructors/operators.

Summary (C++ Programming)

• The study material covers core C++ features: classes, pointers/references, function overloading, operators, the Rule of Three/Five, move semantics, and object destruction.