Yes, it&#39;s called a [`HashSet&lt;T&gt;`][1], and available in version 3.5 of the .NET framework. If you use .NET version 2.0, you can use a Dictionary and set values to &lt;i&gt;null&lt;/i&gt;.


  [1]: http://msdn.microsoft.com/en-us/library/bb359438.aspx

If 3.5 is not an option you could do something like Dictionary &lt; int, int &gt; and simply ignore the value. i&#39;ve done this in 2.0 and i tend to set the value to the same as the key.

If you&#39;re not targeting .NET 3.5, [Power Collections][1] (open source) also provides a Set implementation.


  [1]: http://www.codeplex.com/PowerCollections

or use a SortedList where values have to be unique

There seems to be a problem when [virtualenv][1] is used in PowerShell.

When I try to activate my environment in PowerShell like...
```
env/scripts/activate
```
.. nothing happens. (the shell prompt should have changed as well as the PATH env. variable .)

I guess the problem is that PowerShell spawns a new cmd. process just for running the activate.bat thus rendering the changes `activate.bat` does to the shell dead after it completes. 

Do you have any workarounds for the issue? (I&#39;m sticking with `cmd.exe` for now)


  [1]: http://pypi.python.org/pypi/virtualenv

virtualenv in PowerShell?

I am in the process of fixing some bad UTF-8 encoding. I am currently using PHP 5 and MySQL.

In my database I have a few instances of bad encodings that print like: &#195;ƒ&#194;&#174;

 - The database collation is utf8_general_ci
 - PHP is using a proper UTF-8 header
 - Notepad++ is set to use UTF-8 without BOM
 - database management is handled in [phpMyAdmin][1]
 - not all cases of accented characters are broken

I need some sort of function that will help me map the instances of &#195;ƒ&#194;&#174;, &#195;ƒ&#194;&#173;, &#195;ƒ&#194;&#188; and others like it to their proper accented UTF-8 characters.

  [1]: http://en.wikipedia.org/wiki/PhpMyAdmin


Fixing broken UTF-8 encoding

Is there any data structure in C# that is like a dictionary but that only has a key and doesn&#39;t have a value.  I basically want a list of integers that I can quickly lookup and see if a certain value is in the list.  Granted, for my current use, a List&lt;int&gt; would not cause any performance problem, but it just doesn&#39;t seem to fit well with the intent of what my code is doing.

C# Data Structure Like Dictionary But Without A Value

<p>Is there any data structure in C# that is like a dictionary but that only has a key and doesn't have a value.  I basically want a list of integers that I can quickly lookup and see if a certain value is in the list.  Granted, for my current use, a List<int> would not cause any performance problem, but it just doesn't seem to fit well with the intent of what my code is doing.</int></p>


What is the most elegant code to validate that a string is a valid email address?

C# code to validate email address

Why can&#39;t you use a ref or out parameter in a lambda expression?

I came across the error today and found a workaround but I was still curious why this is a compile-time error.

&gt; [CS1628](https://docs.microsoft.com/en-us/dotnet/csharp/misc/cs1628): Cannot use in ref or out parameter &#39;parameter&#39; inside an anonymous method, lambda expression, or query expression

Here&#39;s a simple example:

    private void Foo()
    {
        int value;
        Bar(out value);
    }

    private void Bar(out int value)
    {
        value = 3;
        int[] array = { 1, 2, 3, 4, 5 };
        int newValue = array.Where(a =&gt; a == value).First();
    }

Cannot use ref or out parameter in lambda expressions

    class Program
    {
        static void Main(string[] args)
        {
            List&lt;Book&gt; books = new List&lt;Book&gt; 
            {
                new Book
                {
                    Name=&quot;C# in Depth&quot;,
                    Authors = new List&lt;Author&gt;
                    {
                        new Author 
                        {
                            FirstName = &quot;Jon&quot;, LastName=&quot;Skeet&quot;
                        },
                         new Author 
                        {
                            FirstName = &quot;Jon&quot;, LastName=&quot;Skeet&quot;
                        },                       
                    }
                },
                new Book
                {
                    Name=&quot;LINQ in Action&quot;,
                    Authors = new List&lt;Author&gt;
                    {
                        new Author 
                        {
                            FirstName = &quot;Fabrice&quot;, LastName=&quot;Marguerie&quot;
                        },
                         new Author 
                        {
                            FirstName = &quot;Steve&quot;, LastName=&quot;Eichert&quot;
                        },
                         new Author 
                        {
                            FirstName = &quot;Jim&quot;, LastName=&quot;Wooley&quot;
                        },
                    }
                },
            };


            var temp = books.SelectMany(book =&gt; book.Authors).Distinct();
            foreach (var author in temp)
            {
                Console.WriteLine(author.FirstName + &quot; &quot; + author.LastName);
            }

            Console.Read();
        }

    }
    public class Book
    {
        public string Name { get; set; }
        public List&lt;Author&gt; Authors { get; set; }
    }
    public class Author
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public override bool Equals(object obj)
        {
            return true;
            //if (obj.GetType() != typeof(Author)) return false;
            //else return ((Author)obj).FirstName == this.FirstName &amp;&amp; ((Author)obj).FirstName == this.LastName;
        }

    }


This is based on an example in &quot;LINQ in Action&quot;. Listing 4.16.

This prints Jon Skeet twice. Why? I have even tried overriding Equals method in Author class. Still Distinct does not seem to work. What am I missing?

Edit:
I have added == and != operator overload too. Still no help.

     public static bool operator ==(Author a, Author b)
        {
            return true;
        }
        public static bool operator !=(Author a, Author b)
        {
            return false;
        }

Distinct not working with LINQ to Objects

I&#39;m not that great with maths and C# doesn&#39;t seem to provide a power-of function
so I was wondering if anyone knows how I would run a calculation like this:

    var dimensions = ((100*100) / (100.00^3.00));

How do I calculate power-of in C#?

I&#39;ve recently purchased a Mac and use it primarily for C# development under VMWare Fusion. With all the nice Mac applications around I&#39;ve started thinking about Xcode lurking just an install click away, and learning Objective-C.

The syntax between the two languages looks very different, presumably because Objective-C has its origins in C and C# has its origins in Java/C++. But different syntaxes can be learnt so that should be OK.

My main concern is working with the language and if it will help to produce well-structured, readable and elegant code. I really enjoy features such as LINQ and var in C# and wonder if there are equivalents or better/different features in Objective-C.

**What language features will I miss developing with Objective-C? What features will I gain?**

**Edit:** The framework comparisons are useful and interesting but a *language* comparison are what this question is really asking (partly my fault for originally tagging with `.net`). Presumably both Cocoa and .NET are very rich frameworks in their own right and both have their purpose, one targeting Mac OS X and the other Windows.

Thank you for the well thought out and reasonably balanced viewpoints so far!

How does Objective-C compare to C#?

What is the difference between the `KeyDown` and `KeyPress` events in .NET?

What&#39;s the difference between KeyDown and KeyPress in .NET?

I&#39;m trying to update one value of a compound primary key from within the entity framework and I&#39;m getting this error: &quot;The property &#39;CustomerID&#39; is part of the object&#39;s key information and cannot be modified. &quot;

Here is my code: 

    Dim customer As Customer = (From c In db.Customer Where c.CustomerID = &quot;xxx&quot; AndAlso c.SiteKey = siteKey).FirstOrDefault
    customer.CustomerID = &quot;fasdfasdf&quot;
    db.SaveChanges()

It seems too simple. Is it true you can&#39;t update a primary key within the entity framework? I can&#39;t find any documentation on the topic. Thanks!

Update primary key value using entity framework

I have a string that looks like this: &quot;9/1/2009&quot;. I want to convert it to a DateTime object (using C#).

This works:

    DateTime.Parse(&quot;9/1/2009&quot;, new CultureInfo(&quot;en-US&quot;));

But I don&#39;t understand why this doesn&#39;t work:

    DateTime.ParseExact(&quot;9/1/2009&quot;, &quot;M/d/yyyy&quot;, null);

There&#39;s no word in the date (like &quot;September&quot;), and I know the specific format, so I&#39;d rather use ParseExact (and I don&#39;t see why CultureInfo would be needed). But I keep getting the dreaded &quot;String was not recognized as a valid DateTime&quot; exception.

Thanks

A little follow up. Here are 3 approaches that work:

    DateTime.ParseExact(&quot;9/1/2009&quot;, &quot;M&#39;/&#39;d&#39;/&#39;yyyy&quot;, null);
    DateTime.ParseExact(&quot;9/1/2009&quot;, &quot;M/d/yyyy&quot;, CultureInfo.InvariantCulture);
    DateTime.Parse(&quot;9/1/2009&quot;, new CultureInfo(&quot;en-US&quot;));

And here are 3 that don&#39;t work:

    DateTime.ParseExact(&quot;9/1/2009&quot;, &quot;M/d/yyyy&quot;, CultureInfo.CurrentCulture);
    DateTime.ParseExact(&quot;9/1/2009&quot;, &quot;M/d/yyyy&quot;, new CultureInfo(&quot;en-US&quot;));
    DateTime.ParseExact(&quot;9/1/2009&quot;, &quot;M/d/yyyy&quot;, null);

So, Parse() works with &quot;en-US&quot;, but not ParseExact... Unexpected?


Why can&#39;t DateTime.ParseExact() parse &quot;9/1/2009&quot; using &quot;M/d/yyyy&quot;

When learning C# for the first time, I was astonished that they had no support for macros in the same capacity that exists in C/C++. I realize that the #define keyword exists in C#, but it is greatly lacking compared to what I grew to love in C/C++. Does anyone know why **real** macros are missing from C#?

*I apologize if this question is already asked in some form or another - I promise I spent a solid 5 minutes looking for duplicates before posting.*

Why aren&#39;t there macros in C#?

I need a data structure that is a LinkedHashMap and is thread safe.

How can I do that ?

Does java have a &quot;LinkedConcurrentHashMap&quot; data structure?

My question relates to [this question][1] asked earlier.  In situations where I am using a queue for communication between producer and consumer threads would people generally recommend using `LinkedBlockingQueue` or `ConcurrentLinkedQueue`?

What are the advantages / disadvantages of using one over the other?

The main difference I can see from an API perspective is that a `LinkedBlockingQueue` can be optionally bounded.

  [1]: https://stackoverflow.com/questions/1426342/need-a-queue-that-can-support-multiple-readers/1426375#1426375

LinkedBlockingQueue vs ConcurrentLinkedQueue

For some compilers, there is a packing specifier for structs, for example ::

&lt;pre&gt;
RealView ARM compiler has &quot;__packed&quot;
Gnu C Compiler has &quot;__attribute__ ((__packed__))&quot;
Visual C++ has no equivalent, it only has the &quot;#pragma pack(1)&quot;
&lt;/pre&gt;

I need something that I can put into the **struct** definition.

Any info/hack/suggestion ? TIA...


Visual C++ equivalent of GCC&#39;s __attribute__ ((__packed__))

There&#39;s a lot of talk about data structures, but I can&#39;t find a simple list of data structures and their practical use out there.  I&#39;m trying to study for an interview and I think this would help me out, along with many others.  I&#39;m looking for something like this:

**Data structure - Example/Used for**

Hash table - fast data lookup ...then give an example

Array - ...

Binary tree - ...

If there is a resource like this somewhere, please let me know.

Thanks!

EDIT: I mean wikipedia is good and all, but on most of the pages they don&#39;t actually list practical uses.  I&#39;m looking for something more than that.

Practical uses of different data structures

Has anyone already implemented a circular buffer in JavaScript? How would you do that without having pointers?

Content Type	Original Author	Original Content on Stackoverflow
Question	Mark Kanof	View Question on Stackoverflow
Solution 1 - C#	Meta-Knight	View Answer on Stackoverflow
Solution 2 - C#	Paul Sasik	View Answer on Stackoverflow
Solution 3 - C#	Eric J.	View Answer on Stackoverflow
Solution 4 - C#	Gregoire	View Answer on Stackoverflow

C# Data Structure Like Dictionary But Without A Value

C# Problem Overview

C# Solutions

Solution 1 - C#

Solution 2 - C#

Solution 3 - C#

Solution 4 - C#

Fixing broken UTF-8 encoding

virtualenv in PowerShell?

Attributions