Vb.net nothing vs null

We use the literal Nothing to indicate a null, nil, nonexistent object. Nothing details. We assign to Nothing, test against it, and ponder nothingness. A NullReferenceException is caused by accessing something on a Nothing value.

First example. This program assigns a String variable to Nothing. This is not an empty string. It is a String object that does not exist. We compare it to Nothing in an If-statement. Part 1 We use the "Is" operator for testing references against Nothing. Part 2 We use the IsNothing function to see if a reference is equal to Nothing. This is another syntax form for the same thing.

This exception not NothingReferenceException is provoked by accessing a member on Nothing. NET never have garbage values. In managed code, like the.

NET Framework, initial values are 0 or Nothing. NET program that uses module-level field Imports System. Nothing can be used with value types such as Integers. When used on values, "Nothing" indicates the default value for the type. So an Integer assigned to Nothing is zero. Tip: Structures are too a value type. When we assign them to Nothing, we get an empty Structure with no bits set to 1. A string in VB. NET can be assigned to Nothing, which is the same concept as Null. We can test a Nothing String with the String.

IsNullOrEmpty method. NET program that uses String. Nothing is not just like null in C. Value types include all numeric data types, Boolean , Char , Date , all structures, and all enumerations. A variable of a reference type stores a reference to an instance of the object in memory. Reference types include classes, arrays, delegates, and strings. For more information, see Value Types and Reference Types.

If a variable is of a value type, the behavior of Nothing depends on whether the variable is of a nullable data type. To represent a nullable value type, add a? Assigning Nothing to a nullable variable sets the value to null. For more information and examples, see Nullable Value Types. If a variable is of a value type that is not nullable, assigning Nothing to it sets it to the default value for its declared type.

If that type contains variable members, they are all set to their default values. The following example illustrates this for scalar types. For numeric types, it means the number zero. For Boolean, it means False. For complex structures, it means that each field will have its default value. The fact that you have mentioned "" seems to suggest that you're interested in Strings specifically. It is better practice to use String.

Empty in VB. In the case of a String variable, it can either be Nothing or it can refer to a String object. If it refers to an object, that String can contain zero, one or more characters. A String with zero characters is still a String object, just as zero is still a value for numeric types. Sometimes people use Nothing and String. Empty interchangeably, but you generally shouldn't. You should use Nothing whether there is logically no value and you should use String.

Empty when there is logically a value that contains no characters. If you want to treat Nothing and String. Empty the same way then you can use the String. IsNullOrEmpty method to detect either. If you want to treat Strings containing only whitespace the same way too, use String. Note that when comparing Strings, you are usually interested in value equality, i. If you're looking for Nothing specifically though, you should use reference equality, because you want to know whether the variable refers to no object.

As for Null it depends what you are actually referring to. My guess is that you are talking about data from a database. NET doesn't use Nothing to represent database nulls because it wouldn't work for value types. If you retrieve nulls from a database using ADO.

Value field. If you're working with ADO. DataRows and data readers have their own methods for detecting nulls, i. Otherwise, you might do this: vb. Value Then Why is my data not saved to my database?

Nothing is not null, but sometimes it behaves sort of like null. This is very complex, and as much as I like to make fun of places where VB is complex, there just isn't a good way to accomplish what they wanted on top of. To understand it, you REALLY need to be comfortable with what the words "reference semantics" and "value semantics" mean.

Think about apples. A big, fat, barrel of apples. Sometimes I just say, "I want to eat an apple". You can take any apple out of the barrel of apples and I'll eat it. You might hold up two of the apples and ask me, "Are these apples the same? That's what "value semantics" means. It means I might compare two different things and decide that they are "the same" for my purposes. Now imagine I have a machine that can magically duplicate apples.

You give me an apple, and I duplicate it. They look, taste, and smell exactly the same. They are the same color, weigh the same, and have marks in the same places. You ask me, "Are these the same apple?

This is still true! Even though they are identical in almost every way, they are still two different apples. This is "reference semantics", where we are only concerned with, "Am I talking about the same object?

In VB. NET, "Nothing" behaves like 'null' in the context of reference semantics. It behaves differently in the context of value semantics. For reference semantics, we're talking about Class types like Form. If you declare the variable without giving it a value, it is automatically assigned Nothing to indicate, "This is an unassigned variable". It also makes little logical sense: unassigned values don't really equal anything , so comparing them even to Nothing is weird.

But it can also include Class types like String, if the implementor goes out of their way and, specifically for String, using some compiler magic. Value types cannot be assigned Nothing as a value. They HAVE to exist. When you compare them to Nothing, the language designers decided to treat Nothing as "the default value for the type".

The "Is" operator only works on reference types. Because "Nothing" isn't a valid value, it gets converted to the default value for the type when I perform the comparison.

I wouldn't rely on this. It's all-around smarter to just not involve Nothing when working with value types. String gets special consideration. It's a Class type, but has special consideration in the compiler to make it have value semantics.

WriteLine foo. Length ' NullReferenceException That's why understanding reference and value semantics is so important. What's happening here: When you make a comparison with "Is", you are asking, "Does this string represent an unassigned variable?

So in this case, the string "is not Nothing", but "has the same value as Nothing". It's still illegal to use the String's methods and properties, because "having the same value as Nothing" is not the same thing as "being nothing".

Generally, you don't have to think about it that deeply, but every now and then it comes up. In short: Nothing is usually serving the same purpose as null. But you can tweak things to make it behave differently. This answer is wrong. You should be using TableAdapter and Dictionaries instead. Strings are reference types that behave like value types, and nothing is much more confusing than that. The following works but every thing else does not.

Rows r. Cells "cfgCluster". Value returns nothing if not assigned.