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How to format a DateTime to a custom string in C#?

The most common method of formatting DateTime objects into custom strings in C# is to use the ToString() method and pass in the format string, which includes: 1. Use standard format strings such as "d", "D", "t", and "T" to quickly implement common date and time formats; 2. Accurately control the output format through custom format strings such as "yyyy-MM-dd", "dd/MM/yyyyHH:mm"; 3. Use CultureInfo to handle format differences in different cultural environments to adapt to multilingual users.

Jul 21, 2025 am 02:46 AM

C# LINQ query syntax vs method syntax

The query syntax or method syntax of LINQ should be selected according to the scene. ① Query syntax is suitable for SQL-like expressions, such as multi-step filtering, projection, sorting, multi-table joining, grouping statistics, etc., with clear and intuitive structure; ② The method syntax is more flexible, supports chain calls and dynamic query conditions construction, and is suitable for aggregation functions, asynchronous operations and scenarios where splicing logic is required; ③ Some operations such as Take, Skip, Any, etc. can only use method syntax. The two functions are the same, and the choice mainly depends on personal habits and specific needs. Reasonable mixing of the two can improve the readability and maintenance of the code.

Jul 21, 2025 am 02:38 AM

How to create a custom exception in C#?

The core of creating custom exceptions in C# is to inherit the Exception class or its subclasses to improve the accuracy of error messages and code maintainability. 1. Custom exceptions can more specifically express error scenarios in business logic, such as InvalidLoginException clearly indicates login problems; 2. Its benefits include improving code readability, better distinguishing error types, and conveniently handling specific exceptions in a unified manner; 3. When creating, you need to inherit the Exception class and implement at least three constructors without parameters, with message parameters, with message and internal exceptions; 4. If serialization support is required, you can implement the ISerializable interface; 5. Throw it when a specific error condition is detected, such as using thrown when verification fails.

Jul 20, 2025 am 01:43 AM

What are lambda expressions in C#?

Lambda expressions are used in C# to write inline, anonymous functions that can be used anywhere you need to delegate. They are simple and flexible, especially suitable for LINQ or asynchronous code. Lambda expressions use the => operator, on the left are input parameters, on the right are expressions or statement blocks; for example, x=>xx represents a lambda that accepts x and returns its squared. If there are multiple parameters, it needs to be wrapped in brackets, such as (intx,inty)=>x y, the type can be omitted and inferred by the compiler. Common uses include LINQ query, event processing, asynchronous programming, etc., such as numbers.Where(n=>n%2==0) filtering even numbers. Unlike the conventional method, lambda

Jul 20, 2025 am 01:20 AM

C# thread vs task: which is better?

In C#, Thread is suitable for underlying scenarios that require fine control of threads, such as long-running services or exclusive resource tasks; Task is recommended for modern application development because it is based on thread pools, supports asynchronous waiting, has advanced functions and is more efficient. 1.Thread directly operates operating system threads, suitable for background services and tasks that clearly require exclusive threads, but create and destroy costs, consume high resources, and lack a built-in asynchronous mechanism. 2.Task automatically utilizes thread pools to save resources, supports cancellation, exception handling, await and other features, and is commonly found in UI optimization, parallel computing, I/O operation and other scenarios. 3. The key difference between the two is: Thread is an underlying implementation, with high resource consumption and fine control granularity, while Task abstraction

Jul 20, 2025 am 01:10 AM

How to parse a string to an enum in C#?

When parsing a string into an enum type in C#, you should preferentially use the Enum.TryParse method to avoid exceptions, and combine Enum.IsDefined to ensure the value is legal. 1. Use Enum.TryParse to safely parse strings, return a Boolean value to indicate success or not, and support ignoring case; 2. Can handle entire numeric strings such as "1", and still ensure that the value actually exists in the enum definition; 3. Enum.IsDefined must explicitly verify whether the parsing result is a valid member of the enum to prevent illegal values from being mistakenly considered valid. Mastering these key points ensures the robustness of the string-to-enum conversion.

Jul 20, 2025 am 12:59 AM

How to read an XML file in C#?

There are three ways to read XML files in C#: XDocument, XmlDocument and DataSet. First, using XDocument can queries and manipulate XML data concisely and efficiently through LINQ, which is suitable for scenarios with clear structures and flexible queries; second, using XmlDocument is an old and stable DOM parsing method that supports XPath query, suitable for situations where nested structures are complex or need to be compatible with old code; third, using DataSet is suitable for XML files with similar database tables, which can be directly mapped into table structures, but is not suitable for data with deep nesting levels; in addition, pay attention to checking file path issues, and it is recommended to use Path.Combine()

Jul 19, 2025 am 01:09 AM

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How to implement a singleton pattern in C#?

Singleton mode has many implementation methods in C# and is suitable for different scenarios. 1. The basic thread safety implementation uses double check locking to ensure that only one instance is created in a multi-threaded environment; 2. The static constructor is simple but not delayed loading; 3. Lazy implementation takes into account both delayed loading and thread safety; 4. Dependency injection is recommended for modern projects, and the life cycle is managed through service registration and management, and the appropriate method is selected according to project needs.

Jul 19, 2025 am 12:31 AM

How to read a CSV file in C#?

There are two ways to read CSV files in C#: one is to use StreamReader to read line by line, which is suitable for simple scenarios; the other is to use the CsvHelper library to process structured data. 1. When using StreamReader, read line by line through ReadLine() method and split fields by delimiter with Split(), but be careful not to correctly parse quoted fields and no type conversion function. 2. CsvHelper supports automatic mapping of class attributes, type conversion, custom mapping, ignoring columns, processing of quoted fields and multiple separators. Notes include: Ensure that the file is UTF-8 encoding; correctly processing the title line; judging null values; it is recommended to read large files line by line to optimize performance.

Jul 19, 2025 am 12:20 AM

What are C# attributes and how to create a custom attribute?

To create your own C# custom properties, you first need to define a class inherited from System.Attribute, then add the constructor and attributes, specify the scope of application through AttributeUsage, and finally read and use them through reflection. For example, define the [CustomAuthor("John")] attribute to mark the code author, use the [CustomAuthor("Alice")] to modify the class or method when applying, and then obtain the attribute information at runtime through the Attribute.GetCustomAttribute method. Common uses include verification, serialization control, dependency injection, and

Jul 19, 2025 am 12:07 AM

What is a C# record struct?

AC#recordstructisalightweight,immutable,value-baseddatastructureintroducedinC#10designedforperformance-criticalscenarios.1.Itcombinesfeaturesofrecordsandstructstoofferimmutability,value-basedequality,andconcisesyntax.2.Storedonthestackorinlinewithinc

Jul 18, 2025 am 01:44 AM

C# dependency injection lifetimes: singleton vs scoped vs transient

The three service life cycles of dependency injection in C# are Singleton, Scoped and Transient. Their respective features and applicable scenarios are as follows: 1. Singleton is globally unique instance, suitable for logging, global configuration and other objects that do not need to be rebuilt, but it is necessary to avoid injecting Scoped or Transient services; 2. Scoped requests one instance per instance, suitable for database context and session-related services, and cannot be used in Singleton; 3. Transient uses a new instance each time, suitable for stateless lightweight services, but attention should be paid to the impact of creation costs on performance.

Jul 18, 2025 am 01:29 AM

What is P/Invoke (Platform Invoke) used for in C#?

P/InvokeinC#isusedtocallfunctionsfromunmanagedDLLs.1.Itenablesinteractionwithlegacyorsystem-levelfunctionsnotavailablein.NET.2.CommonusesincludeaccessingWindowsAPIs,interfacingwithhardware,andcallingthird-partynativelibraries.3.TouseP/Invoke,defineam

Jul 18, 2025 am 01:26 AM

What is the difference between an abstract class and an interface in C#?

In C#, abstract classes are used to share code and provide default behavior, while interfaces are used to define contracts without implementation details. 1. When you need to share code between multiple related classes or provide default implementations, use abstract classes; 2. When multiple unrelated classes need to implement the same behavior or support multiple inheritance, use interfaces; 3. Abstract classes can include implementations, fields and constructors. The interface only defines member signatures (before C# 8.0), but since C# 8.0, the interface can include default implementations; 4. If you need to define "capability" instead of "category" relationships, or if you need to decouple design, you should choose an interface; 5. If you need to add methods in the future without destroying existing code, abstract classes are better; 6. In modern C#, interfaces support default implementations, but interfaces are still recommended for capability definitions, and abstract classes are used for sharing.

Jul 18, 2025 am 12:35 AM