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 family of tools and run-times, 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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7489 votes
67 answers

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!";
4342 votes
34 answers

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
  • 247k
3858 votes
32 answers

How do I cast int to enum in C#?

How do I cast an int to an enum in C#?
lomaxx's user avatar
  • 114k
3390 votes
31 answers

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
3258 votes
20 answers

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
  • 32.8k
2881 votes
13 answers

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 ...
2615 votes
59 answers

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
  • 48.8k
2543 votes
29 answers

Catch multiple exceptions at once?

It is discouraged to simply catch System.Exception. Instead, only the "known" exceptions should be caught. Now, this sometimes leads to unnecessary repetitive code, for example: try { ...
Michael Stum's user avatar
  • 178k
2391 votes
15 answers

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
  • 37.8k
2380 votes
33 answers

How do I generate a random integer in C#?

How do I generate a random integer in C#?
Rella's user avatar
  • 65.1k
2356 votes
41 answers

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
  • 58.1k
2320 votes
31 answers

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
  • 26.7k
2313 votes
23 answers

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
  • 33.1k
2224 votes
74 answers

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?
2149 votes
47 answers

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?
2056 votes
111 answers

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 ...
1998 votes
13 answers

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
1979 votes
18 answers

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
1871 votes
20 answers

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
  • 26.2k
1870 votes
26 answers

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?
1859 votes
15 answers

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
  • 29.3k
1856 votes
4 answers

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
1831 votes
10 answers

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
  • 114k
1721 votes
14 answers

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
  • 34.7k
1719 votes
8 answers

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
  • 22.3k
1695 votes
28 answers

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
  • 25.4k
1687 votes
30 answers

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
  • 344k
1650 votes
15 answers

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
1647 votes
41 answers

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
1623 votes
53 answers

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?
1622 votes
6 answers

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
1618 votes
31 answers

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
1607 votes
24 answers

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
  • 214k
1580 votes
22 answers

'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
  • 153k
1578 votes
47 answers

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
  • 18.2k
1557 votes
19 answers

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
1510 votes
33 answers

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?
1491 votes
42 answers

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("", "/Images/Image.jpg") which would return: "...
Brian MacKay's user avatar
  • 31.2k
1473 votes
296 answers

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 ...
1471 votes
18 answers

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
  • 23.5k
1460 votes
17 answers

Send HTTP POST request in .NET

How can I make an HTTP POST request and send data in the body?
Hooch's user avatar
  • 28.9k
1454 votes
23 answers

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
1442 votes
17 answers

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
  • 189k
1417 votes
22 answers

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
  • 39.4k
1411 votes
31 answers

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
  • 57.5k
1400 votes
14 answers

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
  • 21.4k
1387 votes
26 answers

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
  • 32.5k
1340 votes
20 answers

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
  • 79.8k
1338 votes
4 answers

\d less efficient than [0-9]

I made a comment yesterday on an answer where someone had used [0123456789] in a regex rather than [0-9] or \d. I said it was probably more efficient to use a range or digit specifier than a character ...
weston's user avatar
  • 54.2k
1328 votes
18 answers

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

I have a public async void Foo() method that I want to call from synchronous method. So far all I have seen from MSDN documentation is calling async methods via async methods, but my whole program is ...
Tower's user avatar
  • 99.1k

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