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Questions tagged [c#]

C# (pronounced "see sharp") is a high-level, statically typed, multi-paradigm programming language developed by Microsoft. C# code usually targets Microsoft's .NET ecosystem, which include .NET, .NET Framework, .NET MAUI, and Xamarin among others. Use this tag for questions about code written in C# or about C#'s formal specification.

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7552 votes
68 answers
1.3m views

What is the difference between String and string in C#?

What are the differences between these two, and which one should I use? string s = "Hello world!"; String s = "Hello world!";
4393 votes
36 answers
1.0m views

How to enumerate an enum?

How can you enumerate an enum in C#? E.g. the following code does not compile: public enum Suit { Spades, Hearts, Clubs, Diamonds } public void EnumerateAllSuitsDemoMethod() { ...
Ian Boyd's user avatar
  • 253k
3910 votes
32 answers
2.1m views

How do I cast int to enum in C#?

How do I cast an int to an enum in C#?
lomaxx's user avatar
  • 115k
3448 votes
32 answers
1.3m views

Case insensitive 'Contains(string)'

Is there a way to make the following return true? string title = "ASTRINGTOTEST"; title.Contains("string"); There doesn't seem to be an overload that allows me to set the case ...
Boris Callens's user avatar
3313 votes
20 answers
2.4m views

How to iterate over a dictionary?

I've seen a few different ways to iterate over a dictionary in C#. Is there a standard way?
Jake Stewart's user avatar
  • 33.3k
2901 votes
13 answers
430k views

What are the correct version numbers for C#?

What are the correct version numbers for C#? What came out when? Why can't I find any answers about C# 3.5? This question is primarily to aid those who are searching for an answer using an incorrect ...
2646 votes
59 answers
1.0m views

Deep cloning objects

I want to do something like: MyObject myObj = GetMyObj(); // Create and fill a new object MyObject newObj = myObj.Clone(); And then make changes to the new object that are not reflected in the ...
NakedBrunch's user avatar
  • 49.1k
2583 votes
29 answers
859k views

Catch multiple exceptions at once?

It is discouraged to catch System.Exception errors. Instead, only the "known" exceptions should be caught. This sometimes leads to unnecessary repetitive code, for example: try { WebId = ...
Michael Stum's user avatar
2435 votes
32 answers
3.1m views

How do I generate a random integer in C#?

How do I generate a random integer in C#?
Rella's user avatar
  • 66.3k
2413 votes
15 answers
284k views

Should 'using' directives be inside or outside the namespace in C#?

I have been running StyleCop over some C# code, and it keeps reporting that my using directives should be inside the namespace. Is there a technical reason for putting the using directives inside ...
benPearce's user avatar
  • 38.1k
2367 votes
41 answers
1.2m views

How do I get a consistent byte representation of strings in C# without manually specifying an encoding?

How do I convert a string to a byte[] in .NET (C#) without manually specifying a specific encoding? I'm going to encrypt the string. I can encrypt it without converting, but I'd still like to know ...
Agnel Kurian's user avatar
  • 58.9k
2366 votes
32 answers
2.4m views

Get int value from enum in C#

I have a class called Questions (plural). In this class there is an enum called Question (singular) which looks like this. public enum Question { Role = 2, ProjectFunding = 3, ...
jim's user avatar
  • 27.1k
2329 votes
23 answers
1.3m views

What is the best way to give a C# auto-property an initial value?

How do you give a C# auto-property an initial value? I either use the constructor, or revert to the old syntax. Using the Constructor: class Person { public Person() { Name = "...
bentford's user avatar
  • 33.3k
2255 votes
75 answers
835k views

How do I calculate someone's age based on a DateTime type birthday?

Given a DateTime representing a person's birthday, how do I calculate their age in years?
2173 votes
48 answers
1.4m views

How do I create an Excel (.XLS and .XLSX) file in C# without installing Microsoft Office?

How can I create an Excel spreadsheet with C# without requiring Excel to be installed on the machine that's running the code?
2123 votes
14 answers
1.5m views

AddTransient, AddScoped and AddSingleton Services Differences

I want to implement dependency injection (DI) in ASP.NET Core. So after adding this code to ConfigureServices method, both ways work. What is the difference between the services.AddTransient and ...
Elvin Mammadov's user avatar
2107 votes
114 answers
1.8m views

How do I remedy "The breakpoint will not currently be hit. No symbols have been loaded for this document." warning?

A C# desktop application (on the Visual Studio Express edition) worked, but then it didn't work 5 seconds later. I tried the following: Ensure debug configuration, debug flag, and full debug ...
2014 votes
18 answers
706k views

What do two question marks together mean in C#?

Ran across this line of code: FormsAuth = formsAuth ?? new FormsAuthenticationWrapper(); What do the two question marks mean, is it some kind of ternary operator? It's hard to look up in Google.
Edward Tanguay's user avatar
1908 votes
16 answers
1.5m views

Type Checking: typeof, GetType, or is?

I've seen many people use the following code: Type t = typeof(SomeType); if (t == typeof(int)) // Some code here But I know you could also do this: if (obj1.GetType() == typeof(int)) // Some ...
jasonh's user avatar
  • 30k
1896 votes
20 answers
434k views

Proper use of the IDisposable interface

I know from reading Microsoft documentation that the "primary" use of the IDisposable interface is to clean up unmanaged resources. To me, "unmanaged" means things like database ...
cwick's user avatar
  • 26.5k
1867 votes
26 answers
2.3m views

What is a NullReferenceException, and how do I fix it?

I have some code and when it executes, it throws a NullReferenceException, saying: Object reference not set to an instance of an object. What does this mean, and what can I do to fix this error?
1866 votes
4 answers
122k views

Is there a reason for C#'s reuse of the variable in a foreach?

When using lambda expressions or anonymous methods in C#, we have to be wary of the access to modified closure pitfall. For example: foreach (var s in strings) { query = query.Where(i => i.Prop ...
StriplingWarrior's user avatar
1857 votes
10 answers
1.4m views

Calling the base constructor in C#

If I inherit from a base class and want to pass something from the constructor of the inherited class to the constructor of the base class, how do I do that? For example, if I inherit from the ...
lomaxx's user avatar
  • 115k
1763 votes
14 answers
671k views

What does the [Flags] Enum Attribute mean in C#?

From time to time I see an enum like the following: [Flags] public enum Options { None = 0, Option1 = 1, Option2 = 2, Option3 = 4, Option4 = 8 } I don't understand what ...
Brian Leahy's user avatar
  • 35.2k
1762 votes
8 answers
991k views

How to loop through all enum values in C#? [duplicate]

This question already has an answer here: How do I enumerate an enum in C#? 26 answers public enum Foos { A, B, C } Is there a way to loop through the possible values of Foos? ...
divinci's user avatar
  • 22.9k
1727 votes
29 answers
253k views

Why not inherit from List<T>?

When planning out my programs, I often start with a chain of thought like so: A football team is just a list of football players. Therefore, I should represent it with: var football_team = new ...
Superbest's user avatar
  • 26.2k
1706 votes
30 answers
520k views

What is the difference between const and readonly in C#?

What is the difference between const and readonly in C#? When would you use one over the other?
readonly's user avatar
  • 351k
1662 votes
16 answers
474k views

Why is it important to override GetHashCode when Equals method is overridden?

Given the following class public class Foo { public int FooId { get; set; } public string FooName { get; set; } public override bool Equals(object obj) { Foo fooItem = obj as ...
David Basarab's user avatar
1656 votes
42 answers
204k views

Calculate relative time in C#

Given a specific DateTime value, how do I display relative time, like: 2 hours ago 3 days ago a month ago
1649 votes
53 answers
1.2m views

How do you convert a byte array to a hexadecimal string, and vice versa?

How can you convert a byte array to a hexadecimal string and vice versa?
1646 votes
24 answers
1.8m views

How to Sort a List<T> by a property in the object

I have a class called Order which has properties such as OrderId, OrderDate, Quantity, and Total. I have a list of this Order class: List<Order> objListOrder = new List<Order>(); ...
Shyju's user avatar
  • 217k
1638 votes
31 answers
367k views

When should I use a struct rather than a class in C#?

When should you use struct and not class in C#? My conceptual model is that structs are used in times when the item is merely a collection of value types. A way to logically hold them all together ...
Alex Baranosky's user avatar
1636 votes
6 answers
121k views

Try-catch speeding up my code?

I wrote some code for testing the impact of try-catch, but seeing some surprising results. static void Main(string[] args) { Thread.CurrentThread.Priority = ThreadPriority.Highest; Process....
Eren Ersönmez's user avatar
1603 votes
22 answers
488k views

'Static readonly' vs. 'const'

I've read around about const and static readonly fields. We have some classes which contain only constant values. They are used for various things around in our system. So I am wondering if my ...
Svish's user avatar
  • 156k
1597 votes
47 answers
842k views

How do I update the GUI from another thread?

Which is the simplest way to update a Label from another Thread? I have a Form running on thread1, and from that I'm starting another thread (thread2). While thread2 is processing some files I would ...
CruelIO's user avatar
  • 18.5k
1570 votes
19 answers
611k views

Why is Dictionary preferred over Hashtable in C#?

In most programming languages, dictionaries are preferred over hashtables. What are the reasons behind that?
Nakul Chaudhary's user avatar
1564 votes
33 answers
721k views

What is the difference between a field and a property?

In C#, what makes a field different from a property, and when should a field be used instead of a property?
1520 votes
41 answers
498k views

Path.Combine for URLs?

Path.Combine is handy, but is there a similar function in the .NET framework for URLs? I'm looking for syntax like this: Url.Combine("http://MyUrl.com/", "/Images/Image.jpg") which would return: "...
Brian MacKay's user avatar
  • 31.7k
1493 votes
18 answers
226k views

Virtual member call in a constructor

I'm getting a warning from ReSharper about a call to a virtual member from my objects constructor. Why would this be something not to do?
JasonS's user avatar
  • 23.7k
1491 votes
23 answers
1.3m views

LINQ's Distinct() on a particular property

I am playing with LINQ to learn about it, but I can't figure out how to use Distinct when I do not have a simple list (a simple list of integers is pretty easy to do, this is not the question). What I ...
Patrick Desjardins's user avatar
1486 votes
17 answers
2.5m views

Send HTTP POST request in .NET

How can I make an HTTP POST request and send data in the body?
Hooch's user avatar
  • 29.4k
1474 votes
17 answers
1.7m views

How to calculate difference between two dates (number of days)?

How can one calculate the number of days between two dates in C#?
leora's user avatar
  • 194k
1472 votes
296 answers
756k views

Hidden Features of C#? [closed]

This came to my mind after I learned the following from this question: where T : struct We, C# developers, all know the basics of C#. I mean declarations, conditionals, loops, operators, etc. Some ...
1446 votes
22 answers
509k views

Create Generic method constraining T to an Enum

I'm building a function to extend the Enum.Parse concept that Allows a default value to be parsed in case that an Enum value is not found Is case insensitive So I wrote the following: public static ...
johnc's user avatar
  • 40k
1445 votes
31 answers
761k views

JavaScriptSerializer - JSON serialization of enum as string

I have a class that contains an enum property, and upon serializing the object using JavaScriptSerializer, my json result contains the integer value of the enumeration rather than its string "...
Omer Bokhari's user avatar
  • 58.9k
1436 votes
13 answers
1.1m views

Multiline string literal in C#

Is there an easy way to create a multiline string literal in C#? Here's what I have now: string query = "SELECT foo, bar" + " FROM table" + " WHERE id = 42"; I know PHP has <<<BLOCK ...
Chet's user avatar
  • 21.8k
1414 votes
26 answers
1.2m views

How and when to use ‘async’ and ‘await’

From my understanding one of the main things that async and await do is to make code easy to write and read - but is using them equal to spawning background threads to perform long duration logic? I'...
Dan Dinu's user avatar
  • 33.2k
1391 votes
16 answers
1.3m views

How to call asynchronous method from synchronous method in C#?

I have a public async Task Foo() method that I want to call from a synchronous method. So far all I have seen from MSDN documentation is calling async methods via async methods, but my whole program ...
Tower's user avatar
  • 101k
1371 votes
21 answers
773k views

Difference Between Select and SelectMany

I've been searching the difference between Select and SelectMany but I haven't been able to find a suitable answer. I need to learn the difference when using LINQ To SQL but all I've found are ...
Tarik's user avatar
  • 81k
1351 votes
3 answers
1.5m views

How do I encode and decode a base64 string?

How do I return a base64 encoded string given a string? How do I decode a base64 encoded string into a string?
Kevin Driedger's user avatar

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