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Static LinkingStatic linking involves directly linking all required library files (typically or files) into the executable during compilation. This means the program contains all necessary code for execution, including library function implementations, once compilation is complete.Advantages:High program independence, as no library files need to be present on the system.No additional linking process is required at runtime, potentially resulting in faster startup times.Disadvantages:The executable file size is typically larger due to inclusion of all library code.Updating library files necessitates recompiling the program.Example: In embedded systems or early operating system development, static linking was employed to avoid runtime dependency issues caused by environmental constraints.Dynamic LinkingDynamic linking involves not embedding library code directly into the executable during compilation but instead loading libraries into memory at runtime via a dynamic linker (runtime linker). These libraries are typically dynamic link libraries (e.g., files on Windows or files on Linux).Advantages:The executable file size is smaller, as it does not include actual library code.Libraries can be shared across multiple programs, conserving system resources.Updating or replacing library files does not require recompiling dependent programs.Disadvantages:Additional time is needed at program startup to load required libraries.The program depends on the presence and version of library files; if missing or incompatible, it may fail to run.Example: In modern operating systems, common applications like web browsers or office software typically use dynamic linking to reduce executable size and simplify updates.Summary: Overall, both static and dynamic linking have distinct advantages and disadvantages. The choice depends on the specific requirements of the application, deployment environment, and performance considerations.

In C++, a common approach to convert a char array to a string is by utilizing the standard string class (std::string). Here is a specific example demonstrating how to achieve this:Suppose we have a char array defined as follows:To convert this char array into a std::string object, you can directly employ the constructor of the std::string class, as shown below:This line of code creates a std::string object named , whose content is copied from .Additionally, if you need to specify a particular portion of the string for conversion, you can use another constructor that allows you to define the start position and length:This line of code generates a std::string object containing the content "World".Thus, you can flexibly convert a char array to a std::string object as needed, and leverage various functionalities and operations provided by std::string.

In C++, strongly typed enumerations (also known as enum classes or ) provide enhanced type safety by preventing implicit type conversions. However, there are scenarios where you may need to convert such enumerations to an integer type, such as . This conversion is not automatic and requires explicit handling.Method 1: Using static_castThe most straightforward approach is to use for type conversion, as illustrated below:In this example, the enumeration is a strongly typed enumeration defined based on . When converting the variable to , we use , which retrieves the integer value corresponding to the member (which starts from 0 by default, so corresponds to 1).Method 2: Defining a Conversion FunctionFor frequent conversions, consider defining a conversion function within the class or using a helper function to improve code clarity and maintainability.Here, we define a function that accepts a parameter and returns the corresponding integer value. This allows you to call the function whenever conversion is needed, avoiding repeated use of in the code.ConclusionWhile strongly typed enumerations offer robust type safety, explicit type conversions (such as ) or dedicated conversion functions enable convenient conversion of enumeration values to integers. The choice depends on the specific application context and code maintenance requirements.

The keyword in programming languages like C# is primarily used to provide a safe way to override virtual methods, abstract methods, or other methods in a base class. The purpose of using the keyword is not only to inform the compiler that a method is being overridden but also to enforce a compile-time check to ensure that the method is indeed declared as virtual or abstract in the base class. This helps avoid errors in large projects caused by misspelling method names or changing base class method names.For example, consider a base class and a derived class , as follows:In this example, the method in the class is marked as , indicating that it can be overridden by any class that inherits from it. Using the keyword in the class to override ensures that if the signature of the method in the base class changes (e.g., parameter types or number of parameters), the compiler will immediately throw an error, notifying the developer that the overridden method in the class needs to be updated accordingly.If we mistakenly write the method in the class and attempt to mark it with :At this point, the compiler will throw an error indicating that no overrideable method exists in the base class , thus preventing potential errors early on. This demonstrates the importance of the keyword, as it ensures the accuracy and safety of method overriding.

is a keyword introduced in C++11 for representing null pointers. It is a type-safe null pointer literal of type , which can be converted to any pointer type or boolean type, but not to integer types.Why is better than ?Type Safety: In C++, is actually a macro, typically defined as or , which can lead to type confusion. For example, when a function is overloaded to accept both integer and pointer types, using may result in calling the wrong function version. Using clearly represents a null pointer, avoiding this confusion.Improved Code Clarity and Maintainability: explicitly indicates a null pointer, enhancing code readability and maintainability. During code reviews or refactoring, it clearly distinguishes pointers from integers.Better Compiler Support: is part of the C++ standard, and compilers provide better error checking and optimization. For instance, if is mistakenly used as a non-pointer type, the compiler can generate error messages, preventing runtime errors.Example Illustration:If using to call :This ensures the correct function version is called, avoiding potential errors and confusion. is a new keyword introduced in C++11 for representing null pointers. It is a special type literal known as . The primary purpose of is to replace the macro used in previous versions of C++.Using has several significant advantages over using :Type Safety: is actually a macro, typically defined as or , which can lead to type confusion. For example, when a function is overloaded to accept both integer and pointer types, using may result in calling the wrong function version. Using clearly represents a null pointer, avoiding this confusion.Improved Code Clarity and Maintainability: explicitly indicates a null pointer, enhancing code readability and maintainability. During code reviews or refactoring, it clearly distinguishes pointers from integers.Better Compiler Support: is part of the C++ standard, and compilers provide better error checking and optimization. For instance, if is mistakenly used as a non-pointer type, the compiler can generate error messages, preventing runtime errors.In summary, provides a safer, clearer, and more specific way to represent null pointers, and it is the recommended approach in modern C++ programming to replace the old macro.

In C++, is an ordered associative container implemented using a red-black tree, storing key-value pairs and enabling efficient value retrieval by key. To check if a given key exists in , several methods can be used, as follows:Method 1: Using the MethodThe class provides the method, which takes a key as a parameter and returns an iterator. If the key is found, the iterator points to the element containing the key; otherwise, it equals the iterator returned by .Example Code:In this example, we check if key exists in the map and successfully find and print the corresponding value "banana".Method 2: Using the Methodalso provides the method, which returns the number of elements with the specified key. For , this count can only be or because keys are unique.Example Code:In this example, we attempt to find key , but since it does not exist, the output indicates that the key is not present in the map.Method 3: Using the Method (C++20 and later)Starting from C++20, introduces the method, which directly checks if a key exists, returning or .Example Code (requires C++20 support):In this example, we check if key exists, and since it does, the output correctly indicates that the key is present in the map.In summary, depending on the C++ version used and personal preference, one can choose the appropriate method to determine if a specific key exists in .

The Factory Method pattern is a creational design pattern that defines an interface for creating objects, allowing subclasses to decide which class to instantiate. It defers the instantiation of a class to its subclasses.Implementing the Factory Method pattern in C++ involves the following steps:Define the Product Interface: This is the interface that all concrete products will implement.Create Concrete Product Classes: These classes implement the product interface and provide specific products.Define the Factory Interface: This interface declares a factory method that returns a product interface.Create Concrete Factory Classes: These classes implement the factory interface and decide which concrete product to instantiate.Here's a simple example. We'll implement a factory for creating different types of cars.Step 1: Define the Product InterfaceStep 2: Create Concrete Product ClassesStep 3: Define the Factory InterfaceStep 4: Create Concrete Factory ClassesExample UsageIn this example, we define a interface and two types of cars and , which implement this interface. We also define a interface and two concrete factory classes and , each responsible for creating specific types of cars.This design allows us to create car objects without directly instantiating the car classes, increasing code flexibility and extensibility. The Factory Method pattern is a creational design pattern used to solve the problem of selecting concrete implementation classes for creating instances through an interface. It defines an interface for creating objects (a factory method), allowing subclasses to decide which class to instantiate. The Factory Method pattern defers the instantiation of a class to its subclasses.How to Implement the Factory Method Pattern in C++Step 1: Define the Product InterfaceFirst, define a product interface that describes the operations all concrete products should implement. Here's a simple example with a (vehicle) class:Step 2: Create Concrete Product ClassesNext, create concrete product classes based on the product interface.Step 3: Define the Factory InterfaceDefine a factory class interface that includes a method for creating objects. This method is implemented in subclasses to decide the actual product type to instantiate.Step 4: Create Concrete Factory ClassesDefine concrete factory classes for each product. These factories create specific product objects.Step 5: Use the Factory MethodFinally, in client code, use the factory method to obtain product objects. The client doesn't need to know the concrete product class names; it only needs to know the specific factory to use.SummaryThis example demonstrates how to implement the Factory Method pattern in C++. The pattern allows client code to create product objects through concrete factory instances rather than directly instantiating product objects, increasing code flexibility and extensibility. Adding new product classes is straightforward—just add a concrete product and its corresponding factory. The Factory Method pattern is a commonly used creational design pattern in software engineering that provides an optimal way to create objects. In the Factory Method pattern, object creation is deferred to subclasses.Components of the Factory Method Pattern:Abstract Product: Defines the interface for products.Concrete Product: Implements the abstract product interface.Abstract Creator: Declares the factory method that returns an abstract product.Concrete Creator: Overrides the factory method to return a concrete product instance.Implementation Steps:Here are the steps and code examples for implementing the Factory Method pattern in C++.Step 1: Define Abstract Product and Concrete ProductsStep 2: Define Abstract Creator and Concrete CreatorsStep 3: Use the Factory MethodProblems Solved and Advantages:Decoupling: The Factory Method pattern decouples object creation from usage through interface-based programming.Extensibility: Adding new products requires only adding the corresponding concrete product and factory classes, without modifying existing code, following the Open/Closed Principle.Single Responsibility: Each concrete factory class is responsible for creating only one product, adhering to the Single Responsibility Principle.Example Application Scenarios:In game development, for different level requirements, create various enemy types (e.g., zombies, knights) using the Factory Method pattern.In software development, create different database connections or service objects based on configuration files or environment settings (e.g., test environment, production environment).Through the above examples and explanations, we can see how the Factory Method pattern is implemented in C++ and its importance and convenience in practical applications.

In Java programming, the use of the keyword is crucial because it provides a lightweight synchronization mechanism that ensures variable visibility and prevents instruction reordering in multi-threaded environments.1. Ensure Variable VisibilityWithout the keyword, threads may cache variables in their local memory. Consequently, when one thread updates a variable, other threads might not observe this change. When a variable is declared as , it instructs the JVM and compiler not to cache the variable; instead, every access must read from main memory, and every modification must be written back to main memory immediately. This guarantees that changes made to the variable in one thread are immediately visible to other threads.Example:Suppose there is a flag controlling whether a thread continues execution. If is not declared as , even if the main thread updates to (stopping the controlling thread), the working thread might still see the old value of as due to thread-local caching, causing the program to execute incorrectly.2. Prevent Instruction ReorderingIn the Java Memory Model (JMM), compilers and processors often reorder instructions to improve efficiency. During reordering, the execution order of instructions may change, but the result remains consistent for single-threaded execution. However, this reordering can compromise the correctness of multi-threaded programs. Declaring a variable as prevents the JVM and compiler from reordering operations related to these variables, thereby ensuring the correctness and consistency of the program in multi-threaded environments.Example:Consider a delayed initialization scenario for a singleton pattern using Double-Checked Locking. If the reference to the singleton object is not declared as , it is possible to obtain an incompletely constructed object in some cases. This occurs because the object construction process (allocating memory, initializing the object, and setting the reference to the memory location) may be reordered, allowing other threads to check the reference for non-null and assume the object is initialized, even if it is not fully constructed.Finally, using the keyword ensures the safety and correctness of programs in multi-threaded environments. Although it does not address all concurrency issues, such as atomicity guarantees, it is a simple and effective solution in appropriate scenarios.

In C++, starting from C++11, the standard library provides support for threads. This allows us to use the functionalities provided by the header to create and manage threads. I will demonstrate how to create two threads, each outputting a sequence of numbers, through a simple example.Example CodeCode AnalysisInclude necessary header files:: for input and output operations.: for creating and managing threads.Define the function to be executed by threads:The function accepts two integer parameters to print a sequence of numbers from to .Create and start threads:In the function, we create two threads and , each executing the function with different parameters.Wait for threads to complete:Using the method, the main thread waits for threads and to complete their tasks.Output ResultNotesThe execution order of threads is not fixed; the order of the output may vary depending on how the operating system schedules the threads.When using threads, it is important to consider data sharing and synchronization issues to avoid data races and other concurrency problems.This example demonstrates how to use the thread functionality in the C++ standard library to perform simple parallel tasks.In C++11 and later versions, C++ introduced native multithreading support, including the thread library. This means you can directly create and manage threads in C++ without relying on operating system-specific APIs.Here is a simple example demonstrating how to create a thread and execute a function in C++:In this example, we first include the header file, which is necessary for using the C++ thread library. We then define a function named , which is the code we want to execute in the new thread. In the function, we create a object , which starts executing the function upon construction. By calling , the main thread waits for the newly created thread to complete before proceeding, ensuring thread synchronization.This simple example demonstrates how to use the C++ standard library to create and manage threads. The advantage is that the code is portable and does not depend on the thread management mechanisms of specific operating systems.

In C++, private static data members belong to the class rather than to any specific instance. Therefore, they must be initialized outside the class definition. This is because static member variables are allocated at compile time, not when objects are instantiated.For basic data types, such as , , etc., the following is an example of initializing a private static data member:In the above example, there is a class named with a private static data member . This member is initialized to 0. Every time an object of is instantiated, the constructor increments the value of .If the static member is a class object or requires specific initialization logic, initialization may be more complex. For example, if we have a static member of type , we also need to initialize it outside the class:In this example, we do not provide any initial values in the initialization expression for because the default constructor is sufficient. However, we can also initialize it with specific values, such as which initializes a vector of size 10 with each element set to 0.In summary, private static data members are initialized outside the class definition in the source file, using the syntax . This is a necessary step because static member variables are not part of class instances but are associated with the class itself.

In C++, there are several methods to remove the last character from a string. Here are some common approaches:1. UsingThis is the simplest and most straightforward method. The function directly removes a character from the end of a object.Example code:This code outputs "Hello, World", with the exclamation mark removed.2. UsingThe method can delete a portion of the string. When you specifically need to remove only the last character, you can specify the deletion starting from the end and covering just one character.Example code:This code also outputs "Hello, World".3. Using index operations andBy using , you can adjust the string's size. Setting the size to one less than the current length automatically removes the last character.Example code:This code outputs "Hello, World" as well.All these methods are valid, and the choice depends on the specific use case and personal preference. In most scenarios, is the most direct and efficient approach, especially when you confirm the string is non-empty. For more complex operations, offers greater flexibility.

In C++, we can use (which is part of the header file) to read data from a file line by line. stands for 'input file stream' and is used for reading data from files. Here is a common method for reading files line by line using : First, include the necessary libraries: Then, follow these steps to read the file: Create an object and open a specific file.Use a loop with the function to read the file content line by line.Close the file.Here is a specific example: In the above code: creates an object and attempts to open the file named "example.txt".checks if the file was successfully opened; if not, it outputs an error message and returns 1.reads the file until the end of the file is reached.prints the content of each line.This approach is simple and commonly used, suitable for scenarios where you need to process file data line by line. For example, you can add additional logic during reading to process each line's data, such as analyzing or storing it in a data structure.

The 'override' keyword in C++ is used to ensure that functions in derived classes correctly override virtual functions in the base class. Using the 'override' keyword enables the compiler to verify at compile time that the function in the derived class actually overrides a virtual function in the base class, which helps prevent errors due to spelling mistakes or mismatched function signatures.For example, suppose we have a base class and a derived class, with a virtual function in the base class:In this example, the derived class uses the 'override' keyword to indicate that its function is intended to override the function in the base class . If the signature of the function in the class is changed to , the compiler will report an error because there is no matching virtual function to override, which helps in promptly identifying potential errors.

The standardized memory model in C++11 is primarily designed to address memory consistency issues in multithreaded programs. Before C++11, there was no explicit specification for memory access rules in multithreaded programming, leading to inconsistent behavior across different compilers and platforms, which posed challenges for cross-platform development.Memory Model MeaningThe memory model defines how read and write operations on variables are interpreted and affected in multithreaded programs. It provides a set of rules and protocols to control shared memory behavior across different threads, ensuring data consistency and memory visibility.C++11 Memory Model FeaturesAtomic Operations: C++11 introduced atomic types , whose operations are guaranteed not to be interrupted by thread switches, making them atomic (i.e., indivisible). This is crucial for ensuring operation integrity in multithreaded environments.Memory Orders: C++11 defines several memory orders (e.g., , , ), which provide different levels of guarantees regarding how threads perceive writes from other threads.Memory Barriers (or Fences): This is a synchronization mechanism that ensures the order of certain operations, preventing the compiler or processor from reordering instructions.ImpactEnhanced Portability: With a standardized memory model, the behavior of C++ programs becomes more consistent across different compilers and hardware platforms, significantly improving code portability.Improved Performance: By utilizing atomic operations and fine-grained control over memory orders, developers can write more efficient multithreaded programs, avoiding unnecessary performance overhead from excessive synchronization.Increased Safety: Proper use of C++11's memory model can prevent common data races and synchronization issues in multithreaded programs, reducing error rates and security risks.ExampleSuppose we have a simple counter that needs to be incremented safely across multiple threads:In this example, ensures that the increment operation on is atomic, while provides sufficient guarantees for correctness without introducing unnecessary synchronization overhead.Overall, C++11's memory model, by providing these tools and rules, makes multithreaded program design more intuitive and safe, while also helping developers better leverage the performance of modern multi-core hardware.

Lambda expressions are a highly useful tool in programming, allowing us to define simple anonymous functions. In Python, lambda expressions are commonly used to define small functions that fit within a single line.The basic syntax for lambda expressions is:For example, a function implementing addition can be written using a lambda expression as:Scenarios for Using Lambda Expressions1. Simplifying CodeWhen a simple function is needed for a brief period, using lambda expressions can reduce code length. For instance, when using a custom key in sorting:2. As Parameters to Higher-Order FunctionsMany higher-order functions in Python, such as , , and , accept a function as a parameter. Lambda expressions, as lightweight function definitions, are ideal for these higher-order functions:When to Avoid Using Lambda ExpressionsAlthough lambda expressions are useful, they may not be suitable in the following cases:Complex or hard-to-understand expressions: If the function logic is complex or difficult to grasp, defining a named function is clearer.Functions requiring reuse: If the same logic is used in multiple places, defining a dedicated function is more appropriate.Debugging challenges: Due to the anonymous nature of lambda expressions, debugging can be more difficult.In summary, lambda expressions are a powerful tool that can make code more concise. Using them appropriately can enhance programming efficiency, but it's important to avoid overuse to maintain code readability and maintainability.

1. Keywords and Syntaxtypedef is a traditional keyword in C++ and C for defining type aliases. Its syntax can be somewhat confusing and may hinder readability in complex contexts.Example:using is a new keyword introduced in C++11 for defining type aliases. It offers a more intuitive and readable syntax, particularly in template programming.Example:2. Template Aliasestypedef does not support template aliases, which limits its applicability in template programming.using supports template aliases, making it highly valuable in template programming. It can be used to define type aliases for template parameters.Example:3. ReadabilityThe syntax of typedef can be challenging to read in complex type declarations, especially when dealing with pointers and function pointers.using provides a more intuitive syntax, simplifying the reading and understanding of type aliases, particularly with complex types.SummaryAlthough both and can be used to declare type aliases, offers a more flexible and readable approach, especially in template programming. In modern C++ programming, it is recommended to use for defining type aliases due to its superior readability and flexibility.

In C++17, numerous new features and enhancements have been introduced, significantly improving programming convenience and efficiency. Below, I will list some of the key new features and provide simple examples to illustrate their usage.Structured BindingsStructured bindings enable programmers to destructure multiple variables from arrays or tuples simultaneously, simplifying code. For example:Inline VariablesInline variables primarily address multiple definition issues when declaring global variables in header files. Using the keyword ensures that global variables have a single definition across multiple source files. For example:Filesystem LibraryC++17 officially introduced the filesystem library, simplifying file and directory operations. For example, checking if a file exists:std::optionalprovides a safe way to handle cases where a value may or may not be present, avoiding null pointers. For example:Initialization Statements for if and switchThis allows adding an initialization statement before the condition part of or statements, making the code more concise and readable. For example:Parallel AlgorithmsC++17 added parallel versions of algorithms to the standard library, leveraging modern hardware's multi-core capabilities to accelerate execution. For example, using parallel sorting:These features not only enhance the language's functionality and expressiveness but also further strengthen the ability to write safe and efficient code.

Indeed, as C++ programmers, we should minimize the direct use of the keyword for dynamic memory allocation. This is due to several core reasons:1. Memory Management ComplexityDirect use of requires manual memory management, including proper use of for deallocation. This increases development complexity and can lead to errors such as memory leaks and double frees. For instance, if you forget to release memory allocated via , it remains unrecoverable, potentially causing the program's memory usage to grow indefinitely, known as a memory leak.2. Exception Safety IssuesIn C++, if an exception is thrown during the constructor call rather than caught after , the allocated memory is not automatically released, leading to memory leaks. For example, if you allocate an object array and the constructor throws an exception, previously constructed objects are not destroyed, resulting in complex memory management issues.3. Resource Management (RAII)C++ promotes the Resource Acquisition Is Initialization (RAII) principle, where resource lifetimes are managed through object lifetimes. Using smart pointers (such as and ) automatically manages memory; when the smart pointer object goes out of scope, it deletes the associated memory. This significantly simplifies memory management and exception handling.4. Standard Library ContainersC++'s standard library provides containers like and , which internally manage memory, avoiding direct use of . They offer flexible and efficient memory management, supporting automatic expansion and contraction of elements.5. Modern C++ PracticesSince C++11, the standard has strongly recommended using smart pointers and other resource management classes instead of raw pointers. This is because they provide safer resource management and reduce various errors associated with raw pointers.Example IllustrationSuppose we need to create an object array. Using raw pointers and might look like this:Using modern C++, we can do this:1. Memory Leak RiskAfter allocating memory with , the programmer must manually release it using at the appropriate time. If memory is not released, it leads to memory leaks. Memory leaks gradually consume system memory resources, potentially causing performance degradation or crashes in the program or system.Example:2. Management ComplexityManaging dynamic memory is more complex than static storage (e.g., automatic variables on the stack). Managing and requires careful attention, especially when exceptions are thrown or multiple return paths exist, where errors are easy to occur.Example:3. Performance Issuesand involve operating system memory management, which may be slower than stack memory (automatic allocation and deallocation). Frequent use of and in performance-critical applications can impact overall program performance.4. Modern C++ Resource ManagementModern C++ recommends using smart pointers like and for managing dynamic memory, which automatically release memory and reduce memory leak risks. Additionally, C++'s standard library provides containers like and , which internally manage memory, eliminating the need for direct usage.Example:ConclusionAlthough remains a necessary tool in C++—especially when explicit control over object lifetimes is required—leveraging modern C++ resource management tools and techniques can significantly reduce direct usage, enhancing code safety, maintainability, and performance. Opt for RAII (Resource Acquisition Is Initialization), smart pointers, and standard library containers to simplify resource management and avoid common pitfalls.

The primary distinction lies in the character type used for storage. utilizes , whereas uses .1. Character Sizestd::string uses type, typically occupying 1 byte.std::wstring uses type, with its size depending on the compiler and platform, typically 2 or 4 bytes.2. Usagestd::string is typically used for storing standard ASCII text.std::wstring is typically used for storing text requiring a broader character set, such as Unicode text. This makes more suitable for handling multilingual text.3. Compatibility and Use Casesstd::string was more widely used in early C++ programs because early applications were predominantly English-based.std::wstring is more common in modern applications that require handling multiple languages or complex character sets.4. Functions and MethodsBoth provide similar functions and methods for string manipulation, such as , , , , etc. However, note that some standard library functions may only accept one of or .ExampleSuppose we have an application that needs to handle both English and Chinese characters. Using may be more appropriate because Chinese characters may not be properly represented in when using .ConclusionThe choice between and depends on the specific requirements of the application, particularly concerning language and character set needs. In terms of internationalization and multilingual support, provides broader support.

In C++ programming, the use of the "friend" keyword can be beneficial in specific scenarios, as it primarily allows certain external functions or other classes to access the private or protected members of the current class. This is commonly used in the following cases:Operator Overloading: When overloading certain operators for a class, friend functions are typically employed. For example, overloading input and output operators (>), as the left operand of these operators usually requires a stream object rather than a custom type.Example:Implementing Utility Functions: When utility global functions need to access the private data members of a class, define these functions as friend functions.Example:Implementing Tight Collaboration Between Classes: Sometimes two classes require mutual access to each other's private members, but you do not want to expose these members. In this case, declare one class as a friend of the other.Example:Using the "friend" keyword can enhance the flexibility and efficiency of the program, but it requires caution as it compromises the encapsulation and data hiding of the class, potentially making the code harder to maintain and understand. Therefore, it is recommended to use friend relationships only when absolutely necessary.