Strings, a couple of questions like difference between += and &=

2 Oct 2006 4:12 AM

James

What's the difference between += and &= with reference to strings?

Also, what are string literals? Thanks.

And what are fixed lenth strings? and how do you declare them? Thanks

2 Oct 2006 4:23 AM

Cor Ligthert [MVP]

James,

It is better not to use in visual basic the + with strings. There can be
problems with that when you have option strict of.

string b as string = 10
b += "2"
will result in 12 with option strict of.

string b as string = 10
b &= "2"
will result in 102, mostly the wanted result in this kind of use.

I hope this gives an idea,

Cor

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"James" <jamesburk***@gmail.com> schreef in bericht
news:1159762355.761842.318310@m7g2000cwm.googlegroups.com...
> What's the difference between += and &= with reference to strings?
>
> Also, what are string literals? Thanks.
>
> And what are fixed lenth strings? and how do you declare them? Thanks
>

2 Oct 2006 11:31 AM

Herfried K. Wagner [MVP]

"Cor Ligthert [MVP]" <notmyfirstn***@planet.nl> schrieb:
> It is better not to use in visual basic the + with strings. There can be
> problems with that when you have option strict of.

That's true. In addition you need 'CStr' or 'ToString' calls which are not
always necessary when using '&' because it performs conversion to string
automatically.

> string b as string = 10
> b += "2"
> will result in 12 with option strict of.

No, it will result in "102".

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://classicvb.org/petition/>

4 Oct 2006 1:53 PM

Phill W.

James wrote:

> What's the difference between += and &= with reference to strings?

With Option Strict On - which I would /strongly/ recommend -
None at all.

With Option Strict Off, the + sign can be "misinterpreted" by the
compiler depending on the Type of data values being used.

Dim s As String = "3"
Dim i As Integer = 1

s += i

Should the result be "31" ("3" + CStr(1)) or "4" (CStr(CInt("3") + 1)))?

Stick to "&" - there's no confusion that way.
And turn Option Strict On so you can't trip yourself up.

> Also, what are string literals?

"This is a String Literal" :-)

String Literal ::= A string value that appears /in your code/ with
leading and trailing double-quotes.

> And what are fixed lenth strings? and how do you declare them? Thanks

These are Strings whose value is /always/ a pre-defined number of
characters long, no matter how much you try to put into it.
For example, if you have a five-character fixed-length String, fs:

fs = "A"
?"(" & fs & ")"
(A )

They're useful if you're dealing with flat (say, COBOL-generated) files
where each data field is delimited /only/ by its total length.

Avoid using them if at all possible. Instead, write code that reads and
writes the fixed-length data, but store the values internally in
ordinary, variable-length Strings.

HTH,
Phill W.