Programare II - Curs 7 - Variabile Statice

Programming II - Course 7 - Static

• The static keyword in C++ primarily controls the lifespan and visibility of variables and functions.
• It allows variables to retain their values between function calls.
• It restricts visibility to file or class level.
• It enables shared members within classes.
• Static elements are allocated storage space only once during the program's lifetime, in the static storage area.
• The lifetime of a static variable coincides with the program's lifetime.
• Static variables are initialized only once.
• Their values persist through function calls.

Static Variables

• Examples include static variables within a class, static member variables inside a class, and static methods belonging to a class.

Example Static Variable

• A code example showcasing a static variable named count that increments its value each time the counter() function is called.

Static vs. Global

• A comparison of static and global variables highlighting their scope, persistence, use cases, and encapsulation.
• Static local variables have a limited scope, retaining their values across function calls.
• Global variables are accessible from any function.
• Global variables can introduce unintended modifications, while static variables are more encapsulated within a function's scope.
• Use cases for global or static variables (e.g. counters, state tracking).

Static Member Variables inside a Class

• Static data members have a single value for all objects of the class.
• They share storage, unlike non-static members, which have separate copies per object.
• Static members are initialized outside the class definition.
• Initialization of static members is independent of object creation, rather than depending on the object's constructor.

Example Initialization Static Member

• Code examples illustrate initialization of static member membruStatic.

Static Const

• Constant variables shared across all instances, evaluated during runtime.
• Initialization can be complex, possibly depending on runtime values.

Static ConstExpr

• Guaranteed to be evaluated at compile time.
• Initialization must use compile-time constant expressions.
• Constant expressions help compilers optimize code by replacing the variable with its literal value.

Static Methods Belonging to a Class

• Used for utility functions not dependent on class instances.
• Cannot access non-static data members (due to the lack of this pointer).
• Useful for operations related to the class as a whole or as utility functions.
• Examples include counting class instances.

Example of Static Method Use Case

• Example code illustrating how to use a static method to access total students.

How to Call Static Member Function

• Demonstrate calling static member functions using the class name (e.g., ClassName::methodName()).

Why Access Private Static Variable Outside Class?

• Static members exist independently of class instances; initialization happens outside the object creation.
• private keyword prevents direct access unless initialized correctly.

Resolution Operator (::)

• Allows access to a global variable when a local variable with the same name exists within a function's scope.
• Used to access elements from namespaces like std.
• Enables accessing static variables of a class from outside the class.

Which is the Output?

• Sample code demonstrating static members and how to use them, with code examples that show the results of calling different functions, and how static data can be used in other functions.

Singleton Pattern

• Ensures a class has only one instance and provides a global access point to it.
• Useful in scenarios requiring a single instance to manage global operations (like logging, configurations, or database connections).

Characteristics of Singleton

• A singleton class should have only a single instance.
• That instance should be accessible globally.
• Instance creation is managed internally by the class.

Implementation of Singleton

• Code example showing how to implement a Singleton class in C++.
• The class constructor is made private.
• Using a factory method to return the instance.
• Prevents instantiation using copy constructor.

Components of Singleton

• Private constructor: Prevents direct instantiation using the new operator.
• Static instance: Ensures the instance is created only once.
• Deleted copy operator: Prevents copying or assignment operations.
• getInstance() method: Provides controlled access to the instance.

Thread-safe Singleton

• C++11 ensures static local variables are initialized thread-safely.

Thread-safe vs Non-thread-safe Singleton

• Comparison of thread-safe and non-thread-safe singleton implementations, highlighting the need for thread safety in multithreaded environments.

Lazy Initialization vs. Eager Initialization

• Comparison of lazy vs eager instantiation strategies, discussing advantages and disadvantages, with code demonstrations.

Acest quiz explorează utilizarea cuvântului cheie static în C++. Vei învăța cum variabilele statice pot reține valori între apelurile funcțiilor și cum acestea sunt limitate la nivel de fișier sau clasă. Comparăm variabilele statice cu cele globale pentru a înțelege mai bine comportamentul lor în programare.