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 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.
1,616,438
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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!";
4380
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()
{
...
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votes
32
answers
2.0m
views
3435
votes
32
answers
1.2m
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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 ...
- 92.1k
3305
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?
- 33.3k
2897
votes
13
answers
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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 ...
2638
votes
59
answers
1.0m
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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 ...
- 49k
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votes
29
answers
846k
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 = ...
- 179k
2421
votes
32
answers
3.1m
views
2406
votes
15
answers
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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 ...
- 38.1k
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votes
41
answers
1.2m
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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 ...
- 58.7k
2352
votes
31
answers
2.3m
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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,
...
- 27k
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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 = "...
- 33.2k
2249
votes
75
answers
829k
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?
2167
votes
48
answers
1.4m
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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?
2098
votes
14
answers
1.5m
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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 ...
- 26.6k
2098
votes
113
answers
1.8m
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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 ...
2011
votes
18
answers
695k
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.
- 191k
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votes
16
answers
1.5m
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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 ...
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1891
votes
20
answers
429k
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 ...
- 26.4k
1869
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?
1865
votes
4
answers
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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 ...
- 154k
1856
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 ...
- 115k
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votes
14
answers
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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 ...
- 35.1k
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votes
8
answers
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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?
...
- 22.7k
1718
votes
29
answers
252k
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 ...
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votes
30
answers
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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?
- 349k
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votes
16
answers
471k
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 ...
- 72.8k
1654
votes
42
answers
203k
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?
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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>();
...
- 217k
1637
votes
31
answers
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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 ...
- 49.6k
1635
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....
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1596
votes
22
answers
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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 ...
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votes
47
answers
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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 ...
- 18.4k
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votes
19
answers
607k
views
Why is Dictionary preferred over Hashtable in C#?
In most programming languages, dictionaries are preferred over hashtables.
What are the reasons behind that?
- 25.8k
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votes
33
answers
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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?
1512
votes
41
answers
490k
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:
"...
- 31.6k
1491
votes
18
answers
224k
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?
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votes
17
answers
2.5m
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1478
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 ...
- 139k
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votes
296
answers
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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 ...
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votes
17
answers
1.7m
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How to calculate difference between two dates (number of days)?
How can one calculate the number of days between two dates in C#?
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22
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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 ...
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votes
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answers
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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 "...
- 58.5k
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votes
13
answers
1.0m
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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
...
- 21.7k
1409
votes
26
answers
1.2m
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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'...
- 33k
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votes
16
answers
1.3m
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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 ...
- 101k
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votes
21
answers
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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 ...
- 80.8k
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4
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\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 ...
- 54.5k