    int? x = string.IsNullOrEmpty(cert) ? (int?)null : int.Parse(cert);


I&#39;ve come across the same thing ... I usually just cast the null to (int?) 

    int? x = (string.IsNullOrEmpty(cert)) ? (int?)null: int.Parse(cert);

Basically I&#39;m after [this][1] but for PowerShell instead of bash.

I use git on windows through PowerShell. If possible, I&#39;d like my current branch name to displayed as part of the command prompt.


  [1]: https://stackoverflow.com/questions/816790/append-gits-branch-name-to-command-prompt

How can I display my current git branch name in my PowerShell prompt?

Why would anybody use the &quot;standard&quot; random number generator from [System.Random][1] at all instead of always using the cryptographically secure random number generator from [System.Security.Cryptography.RandomNumberGenerator][2] (or its subclasses because RandomNumberGenerator is abstract)?

Nate Lawson tells us in his Google Tech Talk presentation &quot;[Crypto Strikes Back][3]&quot; at minute 13:11 not to use the &quot;standard&quot; random number generators from Python, Java and C# and to instead use the cryptographically secure version.

I know the difference between the two versions of random number generators (see [question 101337][4]).

But what rationale is there to not always use the secure random number generator? Why use System.Random at all? Performance perhaps?


  [1]: http://msdn.microsoft.com/en-us/library/system.random.aspx
  [2]: http://msdn.microsoft.com/en-us/library/system.security.cryptography.randomnumbergenerator.aspx
  [3]: https://youtu.be/ySQl0NhW1J0?t=788
  [4]: https://stackoverflow.com/questions/101337/what-is-the-difference-between-a-randomly-generated-number-and-secure-randomly-ge

Why use the C# class System.Random at all instead of System.Security.Cryptography.RandomNumberGenerator?

&gt; **Possible Duplicate:**  
&gt; https://stackoverflow.com/questions/858080/nullable-types-and-the-ternary-operator-why-wont-this-work


Why doesn&#39;t this work? Seems like valid code.

      string cert = ddCovCert.SelectedValue;
      int? x = (string.IsNullOrEmpty(cert)) ? null: int.Parse(cert);
      Display(x);

How should I code this? The method takes a Nullable&lt;int&gt;. If the drop down has a string selected I need to parse that into an int otherwise I want to pass null to the method.


C# code won&#39;t compile. No implicit conversion between null and int

> Possible Duplicate: 
> <a href="https://stackoverflow.com/questions/858080/nullable-types-and-the-ternary-operator-why-wont-this-work" target="_blank" rel="noopener noreferrer">https://stackoverflow.com/questions/858080/nullable-types-and-the-ternary-operator-why-wont-this-work</a>
Why doesn't this work? Seems like valid code.
<pre><code class="hljs language-ini"> string cert = ddCovCert.SelectedValue;
 int? x = (string.IsNullOrEmpty(cert)) ? null: int.Parse(cert);
 Display(x);
</code></pre>
How should I code this? The method takes a Nullable<int>. If the drop down has a string selected I need to parse that into an int otherwise I want to pass null to the method.</int>

Let&#39;s say I have a string such as:

    &quot;Hello     how are   you           doing?&quot;

I would like a function that turns multiple spaces into one space.

So I would get:

    &quot;Hello how are you doing?&quot;

I know I could use regex or call 

    string s = &quot;Hello     how are   you           doing?&quot;.replace(&quot;  &quot;,&quot; &quot;);

But I would have to call it multiple times to make sure all sequential whitespaces are replaced with only one.

Is there already a built in method for this?


How to replace multiple white spaces with one white space

In my .NET 2.0 application, I need to check if sufficient permissions exist to create and write to files to a directory. To this end, I have the following function that attempts to create a file and write a single byte to it, deleting itself afterwards to test that permissions do exist.

I figured the best way to check was to actually try and do it, catching any exceptions that occur. I&#39;m not particularly happy about the general Exception catch though, so is there a better or perhaps a more accepted way of doing this?


    private const string TEMP_FILE = &quot;\\tempFile.tmp&quot;;
    
    /// &lt;summary&gt;
    /// Checks the ability to create and write to a file in the supplied directory.
    /// &lt;/summary&gt;
    /// &lt;param name=&quot;directory&quot;&gt;String representing the directory path to check.&lt;/param&gt;
    /// &lt;returns&gt;True if successful; otherwise false.&lt;/returns&gt;
    private static bool CheckDirectoryAccess(string directory)
    {
        bool success = false;
        string fullPath = directory + TEMP_FILE;
    
        if (Directory.Exists(directory))
        {
            try
            {
                using (FileStream fs = new FileStream(fullPath, FileMode.CreateNew, 
                                                                FileAccess.Write))
                {
                    fs.WriteByte(0xff);
                }
    
                if (File.Exists(fullPath))
                {
                    File.Delete(fullPath);
                    success = true;
                }
            }
            catch (Exception)
            {
                success = false;
            }
        }

Checking for directory and file write permissions in .NET

Can I pass a method with an out parameter as a Func?

    public IList&lt;Foo&gt; FindForBar(string bar, out int count) { }

    // somewhere else
    public IList&lt;T&gt; Find(Func&lt;string, int, List&lt;T&gt;&gt; listFunction) { }

Func needs a type so out won&#39;t compile there, and calling listFunction requires an int and won&#39;t allow an out in.

Is there a way to do this?

Func&lt;T&gt; with out parameter

Imagine the following code:

    void DoThis()
    {
        if (!isValid) return;
    
        DoThat();
    }
    
    void DoThat() {
        Console.WriteLine(&quot;DoThat()&quot;);
    }

Is it OK to use a return inside a void method? Does it have any performance penalty? Or it would be better to write a code like this:

    void DoThis()
    {
        if (isValid)
        {
            DoThat();
        }
    }

Is it bad practice to use return inside a void method?

I have read [an article][1] about various shuffle algorithms over at [Coding Horror][2]. I have seen that somewhere people have done this to shuffle a list:

    var r = new Random();
    var shuffled = ordered.OrderBy(x =&gt; r.Next());

Is this a good shuffle algorithm? How does it work exactly? Is it an acceptable way of doing this?

  [1]: http://www.codinghorror.com/blog/archives/001015.html
  [2]: http://www.codinghorror.com/

Is using Random and OrderBy a good shuffle algorithm?


I know this [comment][1] PHP.net.
I would like to have a similar tool like `tr` for PHP such that I can run simply
 
    tr -d &quot; &quot; &quot;&quot;

I run unsuccessfully the function `php_strip_whitespace` by

    $tags_trimmed = php_strip_whitespace($tags);

I run the regex function also unsuccessfully

    $tags_trimmed = preg_replace(&quot; &quot;, &quot;&quot;, $tags);

  [1]: http://fi.php.net/manual/en/function.trim.php#72562
  [2]: http://fi.php.net/manual/en/function.php-strip-whitespace.php

How can strip whitespaces in PHP&#39;s variable?

I know a little C and now I&#39;m taking a look at C++.
I&#39;m used to char arrays for dealing with C strings, but while I look at C++ code I see there are examples using both string type and char arrays:

    #include &lt;iostream&gt;
    #include &lt;string&gt;
    using namespace std;

    int main () {
      string mystr;
      cout &lt;&lt; &quot;What&#39;s your name? &quot;;
      getline (cin, mystr);
      cout &lt;&lt; &quot;Hello &quot; &lt;&lt; mystr &lt;&lt; &quot;.\n&quot;;
      cout &lt;&lt; &quot;What is your favorite team? &quot;;
      getline (cin, mystr);
      cout &lt;&lt; &quot;I like &quot; &lt;&lt; mystr &lt;&lt; &quot; too!\n&quot;;
      return 0;
    }

and

    #include &lt;iostream&gt;
    using namespace std;

    int main () {
      char name[256], title[256];

      cout &lt;&lt; &quot;Enter your name: &quot;;
      cin.getline (name,256);

      cout &lt;&lt; &quot;Enter your favourite movie: &quot;;
      cin.getline (title,256);

      cout &lt;&lt; name &lt;&lt; &quot;&#39;s favourite movie is &quot; &lt;&lt; title;

      return 0;
    }
(both examples from &lt;http://www.cplusplus.com&gt;)

I suppose this is a widely asked and answered (obvious?) question, but it would be nice if someone could tell me what&#39;s exactly the difference between that two ways for dealing with strings in C++ (performance, API integration, the way each one is better, ...).

Thank you.

Difference between string and char[] types in C++

How can I append a word to an already populated string variable with spaces?

Append to string variable

How do you convert System::String to std::string in C++ .NET?

C++ .NET convert System::String to std::string

I have a general question about writing init methods in Objective-C.

I see it everywhere (Apple&#39;s code, books, open source code, etc.) that an init method should check if self = [super init] is not nil before continuing with initialisation.

The default Apple template for an init method is:

    - (id) init
    {
        self = [super init];
        
        if (self != nil)
        {
            // your code here
        }
        
        return self;
    }

Why?

I mean when is init ever going to return nil? If I called init on NSObject and got nil back, then something must be really screwed, right? And in that case, you might as well not even write a program...

Is it really that common that a class&#39; init method may return nil? If so, in what case, and why?

In Objective-C why should I check if self = [super init] is not nil?

In C, there appear to be differences between various values of zero -- `NULL`, `NUL` and `0`.

I know that the ASCII character `&#39;0&#39;` evaluates to `48` or `0x30`.

The `NULL` pointer is usually defined as:

    #define NULL 0

Or

    #define NULL (void *)0

In addition, there is the `NUL` character `&#39;\0&#39;` which seems to evaluate to `0` as well.

Are there times when these three values can not be equal?

Is this also true on 64 bit systems?


What is the difference between NULL, &#39;\0&#39; and 0?

I&#39;m using this code and I&#39;m beyond frustration:

    try {
        $dbh = new PDO(&#39;mysql:dbname=&#39; . DB . &#39;;host=&#39; . HOST, USER, PASS);
        $dbh-&gt;setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        $dbh-&gt;setAttribute(PDO::MYSQL_ATTR_INIT_COMMAND, &quot;SET NAMES &#39;utf8&#39;&quot;);
    }
    catch(PDOException $e)
    {
        ...
    }
    $stmt = $dbh-&gt;prepare(&#39;INSERT INTO table(v1, v2, ...) VALUES(:v1, :v2, ...)&#39;);
    $stmt-&gt;bindParam(&#39;:v1&#39;, PDO::PARAM_NULL); // --&gt; Here&#39;s the problem

`PDO::PARAM_NULL, null, &#39;&#39;,` all of them fail and throw this error:

&gt; **Fatal error**: Cannot pass parameter 2 by reference in /opt/...

Why I am getting Cannot pass parameter 2 by reference error when I am using bindParam with a constant value?

I&#39;m using a stored procedure in MySQL, with a CASE statement.

In the ELSE clause of the CASE ( equivalent to default: ) I want to select and return an empty result set, thus avoiding to throw an SQL error by not handling the ELSE case, and instead return an empty result set as if a regular query would have returned no rows.

So far I&#39;ve managed to do so using something like:  
&lt;code&gt;Select NULL From users Where False&lt;/code&gt;

But I have to name an existing table, like &#39;users&#39; in this example.
It works, but I would prefer a way that doesn&#39;t break if eventually the table name used is renamed or dropped.

I&#39;ve tried `Select NULL Where False` but it doesn&#39;t work.

Using `Select NULL` does not return an empty set, but one row with a column named NULL and with a NULL value.



How to select an empty result set?

This is sample code:

    NSDictionary *myDictionary = [NSDictionary dictionary];
    NSNumber *myNumber = [myDictionary valueForKey: @&quot;MyNumber&quot;];
    NSLog(@&quot;myNumber = %@&quot;, myNumber); // output myNumber = (null)

    if (myNumber == nil)
        NSLog(@&quot;test 1 myNumber == nil&quot;);

    if (myNumber == NULL)
        NSLog(@&quot;test 2 myNumber == NULL&quot;);

    if ([myNumber isEqual:[NSNull null]])
        NSLog(@&quot;test 3 myNumber == [NSNull null]&quot;);

When should I use nil, NULL and [NSNull null]?


When should I use nil and NULL in Objective-C?

I get an xml from the 3rd party and I need to deserialize it into C# object. This xml may contain attributes with value of integer type or empty value: attr=”11” or attr=””. I want to deserialize this attribute value into the property with type of nullable integer. But XmlSerializer does not support deserialization into nullable types. The following test code fails during creation of XmlSerializer with InvalidOperationException {&quot;There was an error reflecting type &#39;TestConsoleApplication.SerializeMe&#39;.&quot;}.

    [XmlRoot(&quot;root&quot;)]
    public class SerializeMe
    {
        [XmlElement(&quot;element&quot;)]
        public Element Element { get; set; }
    }

    public class Element
    {
        [XmlAttribute(&quot;attr&quot;)]
        public int? Value { get; set; }
    }

    class Program {
        static void Main(string[] args) {
            string xml = &quot;&lt;root&gt;&lt;element attr=&#39;&#39;&gt;valE&lt;/element&gt;&lt;/root&gt;&quot;;
            var deserializer = new XmlSerializer(typeof(SerializeMe));
            Stream xmlStream = new MemoryStream(Encoding.ASCII.GetBytes(xml));
            var result = (SerializeMe)deserializer.Deserialize(xmlStream);
        }
    }

When I change type of &#39;Value&#39; property to int, deserialization fails with InvalidOperationException:

&gt;There is an error in XML document (1, 16).

Can anybody advise how to deserialize attribute with empty value into nullable type (as a null) at the same time deserializing non-empty attribute value into the integer? Is there any trick for this so I will not have to do deserialization of each field manually (actually there are a lot of them)?

Update after comment from ahsteele:

 1. [Xsi:nil attribute][1] 

 As far as I know, this attribute works only with XmlElementAttribute - this attribute specifies that the element has no content, whether child elements or body text. But I need to find the solution for XmlAttributeAttribute. Anyway I cannot change xml because I have no control over it.

 2. [bool *Specified property][2]

 This property works only when attribute value is non-empty or when attribute is missing. When attr has empty value (attr=&#39;&#39;) the XmlSerializer constructor fails (as expected).

        public class Element
        {
    	    [XmlAttribute(&quot;attr&quot;)]
    	    public int Value { get; set; }

    	    [XmlIgnore]
    	    public bool ValueSpecified;
        }

 3. [Custom Nullable class like in this blog post by Alex Scordellis][3]

 I tried to adopt the class from this blog post to my problem:

        [XmlAttribute(&quot;attr&quot;)]
        public NullableInt Value { get; set; } 

 But XmlSerializer constructor fails with InvalidOperationException:

 &gt;Cannot serialize member &#39;Value&#39; of type TestConsoleApplication.NullableInt. 

 &gt;XmlAttribute/XmlText cannot be used to encode types implementing IXmlSerializable }

 4. Ugly surrogate solution (shame on me that I wrote this code here :) ):

        public class Element
        {
            [XmlAttribute(&quot;attr&quot;)]
            public string SetValue { get; set; }
    
            public int? GetValue()
            {
                if ( string.IsNullOrEmpty(SetValue) || SetValue.Trim().Length &lt;= 0 )
                    return null;
    
                int result;
                if (int.TryParse(SetValue, out result))
                    return result;
    
                return null;
            }
        }

 But I don’t want to come up with the solution like this because it breaks interface of my  class for its consumers. I would better manually implement IXmlSerializable interface.

Currently it looks like I have to implement IXmlSerializable for the whole Element class (it is big) and there are no simple workaround…


  [1]: http://msdn.microsoft.com/en-us/library/ybce7f69(VS.80).aspx
  [2]: https://stackoverflow.com/questions/703137/how-to-make-a-value-type-nullable-with-xmlserializer-in-c-serialization/703257#703257
  [3]: http://alexscordellis.blogspot.com/2008/11/using-xmlserializer-to-deserialize-into.html


Deserializing empty xml attribute value into nullable int property using XmlSerializer

I&#39;m just revising chapter 4 of C# in Depth which deals with nullable types, and I&#39;m adding a section about using the &quot;as&quot; operator, which allows you to write:

    object o = ...;
    int? x = o as int?;
    if (x.HasValue)
    {
        ... // Use x.Value in here
    }

I thought this was really neat, and that it could improve performance over the C# 1 equivalent, using &quot;is&quot; followed by a cast - after all, this way we only need to ask for dynamic type checking once, and then a simple value check.

This appears not to be the case, however. I&#39;ve included a sample test app below, which basically sums all the integers within an object array - but the array contains a lot of null references and string references as well as boxed integers. The benchmark measures the code you&#39;d have to use in C# 1, the code using the &quot;as&quot; operator, and just for kicks a LINQ solution. To my astonishment, the C# 1 code is 20 times faster in this case - and even the LINQ code (which I&#39;d have expected to be slower, given the iterators involved) beats the &quot;as&quot; code.

Is the .NET implementation of `isinst` for nullable types just really slow? Is it the additional `unbox.any` that causes the problem? Is there another explanation for this? At the moment it feels like I&#39;m going to have to include a warning against using this in performance sensitive situations...

Results:

&gt; Cast: 10000000 : 121  
&gt; As: 10000000 : 2211  
&gt; LINQ: 10000000 : 2143  

Code:

    using System;
    using System.Diagnostics;
    using System.Linq;
    
    class Test
    {
        const int Size = 30000000;
        
        static void Main()
        {
            object[] values = new object[Size];
            for (int i = 0; i &lt; Size - 2; i += 3)
            {
                values[i] = null;
                values[i+1] = &quot;&quot;;
                values[i+2] = 1;
            }
            
            FindSumWithCast(values);
            FindSumWithAs(values);
            FindSumWithLinq(values);
        }
        
        static void FindSumWithCast(object[] values)
        {
            Stopwatch sw = Stopwatch.StartNew();
            int sum = 0;
            foreach (object o in values)
            {
                if (o is int)
                {
                    int x = (int) o;
                    sum += x;
                }
            }
            sw.Stop();
            Console.WriteLine(&quot;Cast: {0} : {1}&quot;, sum, 
                              (long) sw.ElapsedMilliseconds);
        }
    
        static void FindSumWithAs(object[] values)
        {
            Stopwatch sw = Stopwatch.StartNew();
            int sum = 0;
            foreach (object o in values)
            {
                int? x = o as int?;
                if (x.HasValue)
                {
                    sum += x.Value;
                }
            }
            sw.Stop();
            Console.WriteLine(&quot;As: {0} : {1}&quot;, sum, 
                              (long) sw.ElapsedMilliseconds);
        }
    
        static void FindSumWithLinq(object[] values)
        {
            Stopwatch sw = Stopwatch.StartNew();
            int sum = values.OfType&lt;int&gt;().Sum();
            sw.Stop();
            Console.WriteLine(&quot;LINQ: {0} : {1}&quot;, sum, 
                              (long) sw.ElapsedMilliseconds);
        }
    }


Performance surprise with &quot;as&quot; and nullable types

How can I convert the nullable DateTime **dt2** to a formatted string?

    DateTime dt = DateTime.Now;
    Console.WriteLine(dt.ToString(&quot;yyyy-MM-dd hh:mm:ss&quot;)); //works
                                
    DateTime? dt2 = DateTime.Now;
    Console.WriteLine(dt2.ToString(&quot;yyyy-MM-dd hh:mm:ss&quot;)); //gives following error:


&gt; no overload to method ToString takes
&gt; one argument

How can I format a nullable DateTime with ToString()?

please take a look at the following line

    &lt;TextBox Text=&quot;{Binding Price}&quot;/&gt;

This Price property from above is a `Decimal?` (Nullable decimal).

I want that if user deletes the content of the textbox (i.e. enters empty string, it should automatcally update source with null (Nothing in VB).

Any ideas on how I can do it &#39;Xamly&#39;?

Set value to null in WPF binding

There is paradox in the exception description:
Nullable object must have a value (?!)

This is the problem:

I have a `DateTimeExtended` class, 
that has 

    {
      DateTime? MyDataTime;
      int? otherdata;
    
    }

and a constructor

    DateTimeExtended(DateTimeExtended myNewDT)
    {
       this.MyDateTime = myNewDT.MyDateTime.Value;
       this.otherdata = myNewDT.otherdata;
    }

running this code

    DateTimeExtended res = new DateTimeExtended(oldDTE);

throws an `InvalidOperationException` with the message:

&gt;Nullable object must have a value.

`myNewDT.MyDateTime.Value` - is valid and contain a regular `DateTime` object.

What is the meaning of this message and what am I doing wrong?


Note that `oldDTE` is not `null`. I&#39;ve removed the `Value` from `myNewDT.MyDateTime` but the same exception is thrown due to a generated setter.


Content Type	Original Author	Original Content on Stackoverflow
Question	Hcabnettek	View Question on Stackoverflow
Solution 1 - C#	mmx	View Answer on Stackoverflow
Solution 2 - C#	user26901	View Answer on Stackoverflow

C# code won't compile. No implicit conversion between null and int

C# Problem Overview

C# Solutions

Solution 1 - C#

Solution 2 - C#

Why use the C# class System.Random at all instead of System.Security.Cryptography.RandomNumberGenerator?

How can I display my current git branch name in my PowerShell prompt?

Attributions