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.
1,603,452
questions
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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!";
4342
votes
34
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()
{
...
- 247k
3858
votes
32
answers
2.0m
views
3390
votes
31
answers
1.2m
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 ...
- 90.8k
3258
votes
20
answers
2.3m
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?
- 32.8k
2881
votes
13
answers
419k
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 ...
2615
votes
59
answers
999k
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 ...
- 48.8k
2543
votes
29
answers
815k
views
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
{
...
- 178k
2391
votes
15
answers
274k
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 ...
- 37.8k
2380
votes
33
answers
3.0m
views
2356
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 ...
- 58.1k
2320
votes
31
answers
2.3m
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,
...
- 26.7k
2313
votes
23
answers
1.2m
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 = "...
- 33.1k
2224
votes
74
answers
809k
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?
2149
votes
47
answers
1.3m
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?
2056
votes
111
answers
1.7m
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 ...
1998
votes
13
answers
1.3m
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 ...
- 25.4k
1979
votes
18
answers
664k
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.
- 189k
1871
votes
20
answers
417k
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 ...
- 26.2k
1870
votes
26
answers
2.2m
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?
1859
votes
15
answers
1.4m
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 ...
- 29.3k
1856
votes
4
answers
120k
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 ...
- 152k
1831
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 ...
- 114k
1721
votes
14
answers
628k
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 ...
- 34.7k
1719
votes
8
answers
949k
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?
...
- 22.3k
1695
votes
28
answers
247k
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 ...
- 25.4k
1687
votes
30
answers
507k
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?
- 344k
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votes
15
answers
461k
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 ...
- 72.3k
1647
votes
41
answers
200k
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
1623
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?
1622
votes
6
answers
120k
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....
- 38.4k
1618
votes
31
answers
355k
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 ...
- 48.9k
1607
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>();
...
- 214k
1580
votes
22
answers
470k
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 ...
- 153k
1578
votes
47
answers
823k
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 ...
- 18.2k
1557
votes
19
answers
598k
views
Why is Dictionary preferred over Hashtable in C#?
In most programming languages, dictionaries are preferred over hashtables.
What are the reasons behind that?
- 25.6k
1510
votes
33
answers
679k
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?
1491
votes
42
answers
468k
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:
"...
- 31.2k
1473
votes
296
answers
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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 ...
1471
votes
18
answers
218k
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?
- 23.5k
1460
votes
17
answers
2.4m
views
1454
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 ...
- 137k
1442
votes
17
answers
1.6m
views
How to calculate difference between two dates (number of days)?
How can one calculate the number of days between two dates in C#?
- 189k
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votes
22
answers
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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 ...
- 39.4k
1411
votes
31
answers
714k
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 "...
- 57.5k
1400
votes
14
answers
1.0m
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
...
- 21.4k
1387
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'...
- 32.5k
1340
votes
20
answers
730k
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 ...
- 79.8k
1338
votes
4
answers
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views
\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 ...
- 54.2k
1328
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18
answers
1.2m
views
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 ...
- 99.1k