Meaning of _ underscore as a variable prefix in VB.net

Question

What is the meaning of underscore in visual basic? I have this code:

Private _isAuthenticated As Boolean

Is that the same as doing this?

Private isAuthenticated As Boolean

Or does adding the underscore to the front of the name do something special?

Solution 1

It's a convention. A leading _ often indicates that the variable is private to the class. This convention is commonly used in many different languages, not just VB.

In a similar sense, it also indicates that the variable is the local variable behind a property.

However it has no significant meaning to the compiler.

Solution 2

FYI: if you are looking at VB code prior to the .NET era (ie: VB6, of which there is a ton out there) the _ character did have special meaning in that it was a line continuation character. Variables or lines could not begin with an _

Example of VB6 use of _:

Dim str As String
str = "This is part one of a very long string" & _
        "Notice that this is more text" & _
        "AND SOME MORE"

I am pretty sure that in VB.NET the _ continues to function as a line continuation character, however the variable name restriction has obviously been lifted.

Solution 3

At the end of a line, it can be used to split code across multiple lines if it's preceded by a space & the very next character is the new line (_ is the last symbol on the line & followed by a space.

see http://msdn.microsoft.com/en-us/library/ba9sxbw4.aspx

Solution 4

Many use the underscore prefix for field members of the class. These variables should be scoped as Private. This is just a convention however.

Solution 5

The _ (Underscore symbol) is used just because to notify that it is a Private variable.

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Comments

[StealthRT]

Sweet. Thanks for the knowledge, Phil! :)

[StealthRT]

Sweet. Thanks for the knowledge, Peter! :)

[codechurn]

The title of the post is 'Meaning of _ in VB.net', and quoting the question: "Or does adding the _ to the front of the name do something speical?" makes my comment about the fact that the _ can also serve as continuation character relevant and on topic.

[Ozgur Ozturk]

I guess many other people came here from google to find the line continuation usage, hence the upvotes. :) So John, it is relevant since google finds it relevant. :)

[Bugs]

@OzgurOzturk Later versions don't require the underscore to break up code however I guess some people do still use it. I'm not sure when it was phased out exactly (I think 2010). I use 2008 where I need the underscores and then 2013 where I don't. Can get a bit confusing when I haven't used 2008 in a while.

[Vandrey]

Thank you! This was very helpful; especially the link helped a lot.