Nothing = String.Empty (Why are these equal?)

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Why does the first if statement evaluate to true? I know if I use "is" instead of "=" then it won't evaluate to true. If I replace String.Empty with "Foo" it doesn't evaluate to true. Both String.Empty and "Foo" have the same type of String, so why does one evaluate to true and the other doesn't?

    //this evaluates to true
    If Nothing = String.Empty Then

    End If

    //this evaluates to false
    If Nothing = "Foo" Then

    End If

Nothing in VB.net is the default value for a type. The language spec says in section 2.4.7:

Nothing is a special literal; it does not have a type and is convertible to all types in the type system, including type parameters. When converted to a particular type, it is the equivalent of the default value of that type.

So, when you test against String.Empty, Nothing is converted to a string, which has a length 0. The Is operator should be used for testing against Nothing, and String.Empty.Equals(Nothing) will also return false.

How to VB.NET String Null, Indicates whether the specified string is null or an empty string (""). test whether a String is null or its value is String.Empty. It is equivalent to the following code: According to Brad Abrams:. As David implies, there difference between String.Empty and “” are pretty small, but there is a difference. “” actually creates an object, it will likely be pulled out of the string intern pool, but still… while String.Empty creates no object… so if you are really looking for ultimately in memory efficiency, I suggest String.Empty.

Empty string, The Visual Basic runtime usually evaluates Nothing as an empty string (""). The . NET Framework does not, however, and throws an exception� Testing String Value Of Nothing Is Equivalent To String.Empty; When String Variable Was Empty String First One Returns 'nothing' Add Empty String To RadComboBox? Appropriate Way To Set StringBuilder To An Empty String? Convert 0.0 To Empty String? Nothing = String.Empty (Why Are These Equal?) Should This Really Return An Empty String()?

Try this:

Console.WriteLine("Is String.Empty equal to Nothing?: {0}", String.Empty.Equals(Nothing))

The = operator doesn't enforce equal types, whereas the .Equals() method of a string object does, as does the Is operator.

String.IsNullOrEmpty(String) Method (System), It checks for string references that are null or have no data. IsNullOrWhiteSpace tests for whitespace. Strings are reference types and can be equal to null. Often our programs want Important: We cannot check the first char of an empty string. C# - The Benefits Of Using String.Empty? Convert 0.0 To Empty String? Nothing = String.Empty (Why Are These Equal?) Should This Really Return An Empty String()? Assign Empty String To Property With Value Of Nothing; Check If A String Collection Is Empty? Converting A Decimal To An Empty String; Create An Empty String That Is A Certain Length?

Related to this topic, if you use a string variable initialized with "nothing" to be assigned to the property "value" of a SqlParameter that parameter is ignored, not included in the command sent to the server, and a missing parameter error is thrown. If you initialize that variable with string.empty everything goes fine.

//This doesn't work
Dim myString as String = nothing
mySqlCommand.Parameters.Add("@MyParameter", SqlDbType.Char).Value = myString

//This works    
Dim myString as String = string.empty
mySqlCommand.Parameters.Add("@MyParameter", SqlDbType.Char).Value = myString

Nothing and Strings, Prior to PHP 5.5, empty() only supports variables; anything else will result in a parse That means empty() is essentially the concise equivalent to !isset($var) || $var == false. (an empty string); 0 (0 as an integer); 0.0 (0 as a float); "0" (0 as a string) In order to achieve desired (expexted?) results, you need to add __isset ()� It can be confusing to know which of these terms to use. They all mean different things, and are not the same as 0 (zero) or "" (a zero-length string.) Other than Null, they are all part of the VBA language (Visual Basic for Applications.)

C# string.IsNullOrEmpty, IsNullOrWhiteSpace, The Java programming language distinguishes between null and empty strings. An empty string is a string instance of zero length, whereas a null string has no value at all. In this case, an empty string will pass this validation constraint. 39.5.5.13 Case Expressions � 39.5.5.14 NULL Values � 39.5.5.15 Equality Semantics. Identity means, in a nutshell, “are these two variables both equal, and of the same data type?” Generally speaking, we can trust PHP to handle automatically converting our data types — such as changing nulls into empty strings — so that the comparison operator works 99 percent of the time.

empty - Manual, Using laymen's terms, explain the difference between: string empty = ""; string empty = null; string empty = string.Empty; and string.Empty are equal thanks to compiler trickery and they are a string with zero length. null means there is no string at all. level 1 (should I post them here or would you rather not see them?) Strings are reference types and can be equal to null. Often our programs want to handle empty, null, or whitespace strings in special ways. These 2 methods are ideal here.

21.2 Validating Null and Empty Strings, Optionals represent something that has no value. An empty optional integer isn 't equal to 0, -1, 16777216, or any other number – it has nothing at all. string – it definitely has a value, even if that's just the empty string "" .]. Nothing = String.Empty (Why Are These Equal?) Apr 13, 2010. Why does the first if statement evaluate to true? I know if I use "is" instead of "=" then it won't evaluate to true. If I replace String.Empty with "Foo" it doesn't evaluate to true.

Comments
  • Are you using the .Equals() method to compare?
  • I added a code snippet. I don't actually need to do a comparison between null and an empty string, I am just curious as to why that statement evaluated to true.
  • Nothing=String.Empty but String.Empty != Nothing. I just discovered this
  • When using the = operator with a string, VB.NET uses StrCmp, rather than op_Equality. I'd speculate this was for backwards compatibility reasons.
  • What she means to say: VB.NET Nothing = default(T) in C#, not NULL
  • But isn't the default value for String Nothing instead of ""?
  • @recursive: Yes, it is. And that holds for VB as well. The main answer is incorrect and the real reason is given in the comment by Rebecca: VB.NET calls StrCmp when you compare strings with =. This method has special code to handle "" = Nothing as true. If you'd try "".Equals(Nothing) you'd get false.
  • @RebeccaChernoff This answer is completely misleading: default(String) is null, not String.Empty, since String is a ref-type. The correct answer is the one from Heinzi, or in your comment about StrCmp. Please modify your answer, for future reference.
  • This should be the accepted answer. The currently accepted answer is wrong and the correct answer is only given in its comments.
  • set value to DBNull.value instead of nothing
  • It points out a problem that if an external library is not written in VB, the author of the library might not be aware of the ambiguity between nothing and empty string in VB. So when it's used in VB code, users have to be carefull passing nothing or empty string.
  • There is no ambiguity between Nothing and String.Empty in VB. They compare truthy, but they are not the same. Passing Nothing as the parameter value results in the parameter not being sent at all, same does null in C#. Passing DBNull.Value results in the database null being sent as the parameter value, same happens in C#. Passing "" results in an empty string being sent to the database, same in C#.