Nothing as a char of a string

14 Apr 2006 3:42 PM

tommaso.gastaldi

I am extracting some field names from a table of a db (it's an
OledbSchemaguid table).

It occurs for some OleDbSchema driver that

NameDBField = cstr(DataRow.Item(3))

return a string that is composed by the characters of the field name,
for instance MYFIELD plus 1 Nothing. I know that the Nothing is there
because, since I was having a lot of problem with these strange strings
I have scanned them char by char.

This happens for any string extracted from any of the oledbschemaguid
tables using a certain OleDbSchema driver: there is always a char (the
last one ) equal to NOTHING.

Clearly, I would like to avoid the necessity to do the scan to remove
the strange Nothing char. Even the trimEnd instruction does not work,
and these strings cause general malfunnction of the program (for
instance prevent any string concatenation).

I cannot explain this strange thing. Does anybody have any idea how the
Nothing char can appear in the string and what is the best way to get
rid of it?

-t

14 Apr 2006 8:11 PM

tomb

tommaso.gasta***@uniroma1.it wrote:

Show quoteHide quote

>I am extracting some field names from a table of a db (it's an
>OledbSchemaguid table).
>
>It occurs for some OleDbSchema driver that
>
> NameDBField = cstr(DataRow.Item(3))
>
>return a string that is composed by the characters of the field name,
>for instance MYFIELD plus 1 Nothing. I know that the Nothing is there
>because, since I was having a lot of problem with these strange strings
>I have scanned them char by char.
>
>This happens for any string extracted from any of the oledbschemaguid
>tables using a certain OleDbSchema driver: there is always a char (the
>last one ) equal to NOTHING.
>
>Clearly, I would like to avoid the necessity to do the scan to remove
>the strange Nothing char. Even the trimEnd instruction does not work,
>and these strings cause general malfunnction of the program (for
>instance prevent any string concatenation).
>
>I cannot explain this strange thing. Does anybody have any idea how the
>Nothing char can appear in the string and what is the best way to get
>rid of it?
>
>-t
>
>
>

That nothing character is the \0 from C++ and similar languages that
terminate a string with the NULL character. VB doesn't really
understand this character, and can't concatenate anything to it.
Try using this function for anything you get back from the OleDbSchema:

Private Function StripTerminator(ByVal strString As String) As String
    'Strings returned from Windows end in chr(0). It needs to be
removed for VB.'

        Dim intZeroPos As Integer

        intZeroPos = InStr(strString, Chr$(0))
        If intZeroPos > 0 Then
            StripTerminator = Left$(strString, intZeroPos - 1)
        Else
            StripTerminator = strString
        End If
End Function

Tom

14 Apr 2006 8:45 PM

tommaso.gastaldi

Thank you Tom! :) that's very enlighting, and thank you very much for
the code you kindly provided, which is certainly faster than the one I
was using temporarily:

    Dim Scanner As New System.Text.StringBuilder

    Function RemoveNothing(ByVal Text As String) As String
        Scanner.Length = 0
        For Each u As Char In Text
            If Not u = Nothing Then Scanner.Append(u)
        Next u
        Return Scanner.ToString
    End Function

Actually I was afraid that some strange chars could be found in any
position. But your explanation has clarified that it can be found only
at the end (I hope!).

Actually, I do not understand why that character is there, while in all
the other OleDB provider I have tried (I tried almost all of them) I
never saw it.

In this case I am talking about MyOleDB, the one available for MYSQL
(it seems quite primitive, must say). It is strange that I did not hear
much complaint around: probably not many people are actually using it.

Is that a bug of the OLEDB provider or it is possible in principle
that, given the specifications to create OleDB Drivers, that strange
terminator chars could be found in the SchemaGuid tables?

Thank you VERY much!!

-tom

tomb ha scritto:

Show quoteHide quote

> tommaso.gasta***@uniroma1.it wrote:
>
> >I am extracting some field names from a table of a db (it's an
> >OledbSchemaguid table).
> >
> >It occurs for some OleDbSchema driver that
> >
> > NameDBField = cstr(DataRow.Item(3))
> >
> >return a string that is composed by the characters of the field name,
> >for instance MYFIELD plus 1 Nothing. I know that the Nothing is there
> >because, since I was having a lot of problem with these strange strings
> >I have scanned them char by char.
> >
> >This happens for any string extracted from any of the oledbschemaguid
> >tables using a certain OleDbSchema driver: there is always a char (the
> >last one ) equal to NOTHING.
> >
> >Clearly, I would like to avoid the necessity to do the scan to remove
> >the strange Nothing char. Even the trimEnd instruction does not work,
> >and these strings cause general malfunnction of the program (for
> >instance prevent any string concatenation).
> >
> >I cannot explain this strange thing. Does anybody have any idea how the
> >Nothing char can appear in the string and what is the best way to get
> >rid of it?
> >
> >-t
> >
> >
> >
> That nothing character is the \0 from C++ and similar languages that
> terminate a string with the NULL character. VB doesn't really
> understand this character, and can't concatenate anything to it.
> Try using this function for anything you get back from the OleDbSchema:
>
> Private Function StripTerminator(ByVal strString As String) As String
>     'Strings returned from Windows end in chr(0). It needs to be
> removed for VB.'
>
>         Dim intZeroPos As Integer
>
>         intZeroPos = InStr(strString, Chr$(0))
>         If intZeroPos > 0 Then
>             StripTerminator = Left$(strString, intZeroPos - 1)
>         Else
>             StripTerminator = strString
>         End If
> End Function
>
>
> Tom

14 Apr 2006 11:07 PM

Dennis

You might try mystring = mystring.replace(chr(0), "")

--
Dennis in Houston

Show quoteHide quote

"tommaso.gasta***@uniroma1.it" wrote:

>
> Thank you Tom! :) that's very enlighting, and thank you very much for
> the code you kindly provided, which is certainly faster than the one I
> was using temporarily:
>
>     Dim Scanner As New System.Text.StringBuilder
>
>     Function RemoveNothing(ByVal Text As String) As String
>         Scanner.Length = 0
>         For Each u As Char In Text
>             If Not u = Nothing Then Scanner.Append(u)
>         Next u
>         Return Scanner.ToString
>     End Function
>
> Actually I was afraid that some strange chars could be found in any
> position. But your explanation has clarified that it can be found only
> at the end (I hope!).
>
> Actually, I do not understand why that character is there, while in all
> the other OleDB provider I have tried (I tried almost all of them) I
> never saw it.
>
> In this case I am talking about MyOleDB, the one available for MYSQL
> (it seems quite primitive, must say). It is strange that I did not hear
> much complaint around: probably not many people are actually using it.
>
> Is that a bug of the OLEDB provider or it is possible in principle
> that, given the specifications to create OleDB Drivers, that strange
> terminator chars could be found in the SchemaGuid tables?
>
> Thank you VERY much!!
>
> -tom
>
>
>
>
> tomb ha scritto:
>
> > tommaso.gasta***@uniroma1.it wrote:
> >
> > >I am extracting some field names from a table of a db (it's an
> > >OledbSchemaguid table).
> > >
> > >It occurs for some OleDbSchema driver that
> > >
> > > NameDBField = cstr(DataRow.Item(3))
> > >
> > >return a string that is composed by the characters of the field name,
> > >for instance MYFIELD plus 1 Nothing. I know that the Nothing is there
> > >because, since I was having a lot of problem with these strange strings
> > >I have scanned them char by char.
> > >
> > >This happens for any string extracted from any of the oledbschemaguid
> > >tables using a certain OleDbSchema driver: there is always a char (the
> > >last one ) equal to NOTHING.
> > >
> > >Clearly, I would like to avoid the necessity to do the scan to remove
> > >the strange Nothing char. Even the trimEnd instruction does not work,
> > >and these strings cause general malfunnction of the program (for
> > >instance prevent any string concatenation).
> > >
> > >I cannot explain this strange thing. Does anybody have any idea how the
> > >Nothing char can appear in the string and what is the best way to get
> > >rid of it?
> > >
> > >-t
> > >
> > >
> > >
> > That nothing character is the \0 from C++ and similar languages that
> > terminate a string with the NULL character. VB doesn't really
> > understand this character, and can't concatenate anything to it.
> > Try using this function for anything you get back from the OleDbSchema:
> >
> > Private Function StripTerminator(ByVal strString As String) As String
> >     'Strings returned from Windows end in chr(0). It needs to be
> > removed for VB.'
> >
> >         Dim intZeroPos As Integer
> >
> >         intZeroPos = InStr(strString, Chr$(0))
> >         If intZeroPos > 0 Then
> >             StripTerminator = Left$(strString, intZeroPos - 1)
> >         Else
> >             StripTerminator = strString
> >         End If
> > End Function
> >
> >
> > Tom
>
>

15 Apr 2006 12:04 AM

tommaso.gastaldi

Thanks Dennis! :)

at this point I am really curious to get an idea of the respective
performance of the 3 solutions which
we have seen (although they are not really equivalent) ...

let's see ... here is the result of a quick and primitive test :

        'TIME:
        'RemoveNothing1 - around 10.000
        'RemoveNothing2 - around     670
        'RemoveNothing3 - around   1200

mmm .... actually I expected the replace to do better, as anyway
"InStr" id done through linear search   (?) ...

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click

        Dim t As Date = Now

        Dim s As String = "khjlkjddsdvasdvfasbasdsd" & _
                          "sdfsdsdfgbsdfgsdfhlkhlhlhlkhj" _
                          & Chr(0) & Chr(0)

        For i As Integer = 0 To 1000000
            RemoveNothing3(s)
        Next i

        MsgBox(Now.Subtract(t).TotalMilliseconds)

    End Sub

    Dim Scanner As New System.Text.StringBuilder
    Function RemoveNothing1(ByVal Text As String) As String
        Scanner.Length = 0
        For Each u As Char In Text
            If Not u = Nothing Then Scanner.Append(u)
        Next u
        Return Scanner.ToString
    End Function

    Private Function RemoveNothing2(ByVal strString As String) As
String
        'Strings returned from Windows end in chr(0). It needs to be
        'removed for VB.'

        Dim intZeroPos As Integer

        intZeroPos = InStr(strString, Chr(0))
        If intZeroPos > 0 Then
            Return Microsoft.VisualBasic.Left(strString, intZeroPos -
1)
        Else
            Return strString
        End If

    End Function

    Private Function RemoveNothing3(ByVal mystring As String) As String
        Return mystring.Replace(Chr(0), "")
    End Function

16 Apr 2006 12:32 AM

Dennis

Thanks for sharing your timing test...it's as I suspected it would be.
However, if you have only a chr(0) at the end of the string, you might try
mystring=mystring.trimend(chr(0)). This might be faster. Also, if there are
several embedded chr(0)'s in the string, other than at the end, then I
suspect method 3 with the .replace method will be faster than 2.

--
Dennis in Houston

Show quoteHide quote

"tommaso.gasta***@uniroma1.it" wrote:

> Thanks Dennis! :)
>
> at this point I am really curious to get an idea of the respective
> performance of the 3 solutions which
> we have seen (although they are not really equivalent) ...
>
> let's see ... here is the result of a quick and primitive test :
>
>         'TIME:
>         'RemoveNothing1 - around 10.000
>         'RemoveNothing2 - around     670
>         'RemoveNothing3 - around   1200
>
> mmm .... actually I expected the replace to do better, as anyway
> "InStr" id done through linear search   (?) ...
>
>
>     Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
> System.EventArgs) Handles Button1.Click
>
>         Dim t As Date = Now
>
>         Dim s As String = "khjlkjddsdvasdvfasbasdsd" & _
>                           "sdfsdsdfgbsdfgsdfhlkhlhlhlkhj" _
>                           & Chr(0) & Chr(0)
>
>         For i As Integer = 0 To 1000000
>             RemoveNothing3(s)
>         Next i
>
>         MsgBox(Now.Subtract(t).TotalMilliseconds)
>
>     End Sub
>
>     Dim Scanner As New System.Text.StringBuilder
>     Function RemoveNothing1(ByVal Text As String) As String
>         Scanner.Length = 0
>         For Each u As Char In Text
>             If Not u = Nothing Then Scanner.Append(u)
>         Next u
>         Return Scanner.ToString
>     End Function
>
>     Private Function RemoveNothing2(ByVal strString As String) As
> String
>         'Strings returned from Windows end in chr(0). It needs to be
>         'removed for VB.'
>
>         Dim intZeroPos As Integer
>
>         intZeroPos = InStr(strString, Chr(0))
>         If intZeroPos > 0 Then
>             Return Microsoft.VisualBasic.Left(strString, intZeroPos -
> 1)
>         Else
>             Return strString
>         End If
>
>     End Function
>
>     Private Function RemoveNothing3(ByVal mystring As String) As String
>         Return mystring.Replace(Chr(0), "")
>     End Function
>
>

16 Apr 2006 1:42 AM

tommaso.gastaldi

I tried it.
Under same conditions, it's around 600.

Yes, method 3 is more general, as it replaces vbNullChar everywhere.
The last method proposed is probably the one which sufficies in this
specific
situation ("bug" in MyOleDB driver).

The key thing has been noticing (Tomb) that the "nothing" value is
caused by the terminator
vbNullchar (\0) ...

-tom

17 Apr 2006 1:55 AM

tomb

tommaso.gasta***@uniroma1.it wrote:

Show quoteHide quote

>I tried it.
>Under same conditions, it's around 600.
>
>Yes, method 3 is more general, as it replaces vbNullChar everywhere.
>The last method proposed is probably the one which sufficies in this
>specific
>situation ("bug" in MyOleDB driver).
>
>The key thing has been noticing (Tomb) that the "nothing" value is
>caused by the terminator
>vbNullchar (\0) ...
>
>-tom
>
>
>

Actually, this is not a bug at all. The C related environments all use
the chr(0) as a string terminator, as does the Windows OS. If you ever
used the Windows dll call to read a registry entry, it is returned from
the OS with that very terminator. MySql obviously was written in that
kind of language. VB actually has that terminator, it's just that we
don't see it - it is hidden fom us by the development environment. VB
uses a string descriptor rather than the actual array of characters
holding the string. I'm sure the originators of VB had a very good
reason for doing this, but it can get in the way of playing nice with
the other guys.
Anyway, these were some interesting approaches to the situation. It was
a learning experience for me also. And thanks for the recognition.

Tom

17 Apr 2006 2:25 PM

tommaso.gastaldi

Hi Tom :)

I understood that. What I meant talking about "bug" is the following.

If you extract (through the command
OleDbConnection.GetOleDbSchemaTable) the SchemaTables using ANY other
OleDb driver (Oracle, Sybase, VFP, SQL server, jet, etc...) you will
get a clean list of items.

When you use MyOleDB OleDbDriver for MYSQL, * and only for this one * ,
each string in the schema shows that problem (a vbNullChar appended to
each string).

You can make a trial yourself (the driver is here:
http://sourceforge.net/projects/myoledb/ ). I use something like:

            Try
                Using SchemaGuidColumns As DataTable =
..OleDbConnection.GetOleDbSchemaTable(System.Data.OleDb.OleDbSchemaGuid.Columns,
New Object() {})
'...

The connection string for MySQL is like that:

                Me.ConnectionString = "Provider=MySQLProv" & _
                                      ";User ID=" & UserId & _
                                      ";Password=" & Password & _
                                      ";Location=" &
Me.ServiceNameServerNameLocation & _
                                      ";Data Source=" &
Me.DatabaseCatalog

Since this happens only for MyOLEDB driver, I suspect that this
situation may be defined as "bug", even though I do not know the reason
why this happens (perhaps the programmer of the driver has used 2
terminators (??) )

Any idea?

-tommaso

17 Apr 2006 8:24 PM

tomb

I haven't encountered any of this. It is only my C++ experience that
enabled me to decypher what that ending character is. But I appreciate
you sharing the work you've done with this, it will certainly be useful
in the very near future, as I am beginning a project that uses MySql as
the back-end.

Tom

tommaso.gasta***@uniroma1.it wrote:

Show quoteHide quote

>Hi Tom :)
>
>I understood that. What I meant talking about "bug" is the following.
>
>If you extract (through the command
>OleDbConnection.GetOleDbSchemaTable) the SchemaTables using ANY other
>OleDb driver (Oracle, Sybase, VFP, SQL server, jet, etc...) you will
>get a clean list of items.
>
>When you use MyOleDB OleDbDriver for MYSQL, * and only for this one * ,
>each string in the schema shows that problem (a vbNullChar appended to
>each string).
>
>You can make a trial yourself (the driver is here:
>http://sourceforge.net/projects/myoledb/ ). I use something like:
>
>            Try
>                Using SchemaGuidColumns As DataTable =
>.OleDbConnection.GetOleDbSchemaTable(System.Data.OleDb.OleDbSchemaGuid.Columns,
>New Object() {})
>'...
>
>The connection string for MySQL is like that:
>
>                Me.ConnectionString = "Provider=MySQLProv" & _
>                                      ";User ID=" & UserId & _
>                                      ";Password=" & Password & _
>                                      ";Location=" &
>Me.ServiceNameServerNameLocation & _
>                                      ";Data Source=" &
>Me.DatabaseCatalog
>
>Since this happens only for MyOLEDB driver, I suspect that this
>situation may be defined as "bug", even though I do not know the reason
>why this happens (perhaps the programmer of the driver has used 2
>terminators (??) )
>
>Any idea?
>
>-tommaso
>
>
>

17 Apr 2006 9:43 PM

tommaso.gastaldi

Good. When you find out problems on that area, let's share them (just
drop an e-mail or post here), I am very interested on these (or
actually, on their solution :) and, for some, I already have some
solutions... )

for instance, another thing I have noticed is that MyOledb does not
seem to like at all table aliases ...

-tom

tomb ha scritto:

Show quoteHide quote

> I haven't encountered any of this. It is only my C++ experience that
> enabled me to decypher what that ending character is. But I appreciate
> you sharing the work you've done with this, it will certainly be useful
> in the very near future, as I am beginning a project that uses MySql as
> the back-end.
>
> Tom
>
> tommaso.gasta***@uniroma1.it wrote:
>
> >Hi Tom :)
> >
> >I understood that. What I meant talking about "bug" is the following.
> >
> >If you extract (through the command
> >OleDbConnection.GetOleDbSchemaTable) the SchemaTables using ANY other
> >OleDb driver (Oracle, Sybase, VFP, SQL server, jet, etc...) you will
> >get a clean list of items.
> >
> >When you use MyOleDB OleDbDriver for MYSQL, * and only for this one * ,
> >each string in the schema shows that problem (a vbNullChar appended to
> >each string).
> >
> >You can make a trial yourself (the driver is here:
> >http://sourceforge.net/projects/myoledb/ ). I use something like:
> >
> >            Try
> >                Using SchemaGuidColumns As DataTable =
> >.OleDbConnection.GetOleDbSchemaTable(System.Data.OleDb.OleDbSchemaGuid.Columns,
> >New Object() {})
> >'...
> >
> >The connection string for MySQL is like that:
> >
> >                Me.ConnectionString = "Provider=MySQLProv" & _
> >                                      ";User ID=" & UserId & _
> >                                      ";Password=" & Password & _
> >                                      ";Location=" &
> >Me.ServiceNameServerNameLocation & _
> >                                      ";Data Source=" &
> >Me.DatabaseCatalog
> >
> >Since this happens only for MyOLEDB driver, I suspect that this
> >situation may be defined as "bug", even though I do not know the reason
> >why this happens (perhaps the programmer of the driver has used 2
> >terminators (??) )
> >
> >Any idea?
> >
> >-tommaso
> >
> >
> >