vb.net string concatenation string + function output + string = string + function output and no more

Question

The following output produces a string with no closing xml tag.

m_rFlight.Layout = m_rFlight.Layout + "<G3Grid:Spots>" + Me.gvwSpots.LayoutToString() + "</G3Grid:Spots>"

This following code works correctly

m_rFlight.Layout = m_rFlight.Layout + "<G3Grid:Spots>" + Me.gvwSpots.LayoutToString()
m_rFlight.Layout = m_rFlight.Layout + "</G3Grid:Spots>" 'add closing tag

What's going on here, what's the reason the first example isnt working and the second is?

The gvwSpots.LayoutToString() function returns a string.

Joel Etherton · Accepted Answer · 2013-09-06 14:22:38Z

1

As Meta-Knight said, except that I would recommend using the StringBuilder class:

Dim myString As New System.Text.StringBuilder

myString.Append("<G3Grid:Spots>")
myString.Append(Me.gvwSpots.LayoutToString())
myString.Append("</G3Grid:Spots>")

m_rFlight.Layout = myString.ToString()

edited Sep 6, 2013 at 14:22

answered Feb 4, 2010 at 16:08

Joel Etherton

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2 Comments

CodingBarfield Over a year ago

So I ask why the code is doing something and you suggest using a stringbuilder? The code gets executed once for every user, using the stringbuilder for performance benefits won't be that usefull. The final string is no larger then a couple of 1000 characters.

Joel Etherton Over a year ago

@Barfieldmv: Yah, like I said, I agree with Meta-Knight. It looked to me like you're you having goofy append issues with your string possibly because of a typing problem. Using StringBuilder might help alleviate that by ensuring that the output is definitely a string. Other than that, you shouldn't be using + to concatenate (as other have said). I don't recommend StringBuilder for performance in this case. I recommend it for type safety.

Meta-Knight · Accepted Answer · 2010-02-04 16:02:32Z

1

Consider the following code that should be the equivalent of your code:

Dim someString As String = String.Empty

someString = someString + "<G3Grid:Spots>" + "SomeValue" + "</G3Grid:Spots>"

Console.WriteLine(someString)

someString = String.Empty
someString = someString + "<G3Grid:Spots>" + "SomeValue"
someString = someString + "</G3Grid:Spots>"

Console.WriteLine(someString)

I tested it and in both cases the output is: <G3Grid:Spots>SomeValue</G3Grid:Spots>

If you don't get the same results then it's because either m_rFlight.Layout is not a string, or Me.gvwSpots.LayoutToString() doesn't return a string and does something strange with the + operator. You can use the & operator instead to make sure that only string concatenation is performed.

answered Feb 4, 2010 at 16:02

Meta-Knight

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1 Comment

xpda Over a year ago

I would agree -- replace the "+" with "&" for string concatenation, or you may end up with some inadvertant numeric addition sometime.

xpda · Accepted Answer · 2010-02-06 16:38:52Z

0

You can use string.concat

m_rFlight.Layout = string.concat(m_rFlight.Layout, "<G3Grid:Spots>",_
  Me.gvwSpots.LayoutToString(), "</G3Grid:Spots>")

or, as Meta-Knight mentioned, & instead of +. (It will always convert to string before concatenation.)

m_rFlight.Layout &= "<G3Grid:Spots>" & Me.gvwSpots.LayoutToString() & "</G3Grid:Spots>"

answered Feb 6, 2010 at 16:38

xpda

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