Re: To cast or not to cast?

Creating a new pointer is not enough. You need to allocate memory and
assign value pointing to it to the pointer.
You might allocate native memory via P/Invoke (which you would have to free
at some point).
Or, you can obtain a pointer to a managed array you already have.
Before you pass this pointer to a native code, you have to pin managed
memory so GC won't move the array.
You can use GCHandle class for it or you can use unsafe code.
I would recommend using Fixed() with unsafe pointer. That would pin and
unpin the array automatically.
GCHandle has a bug (returns incorrect pointer - there's a workaround) and
it's not automatic.

Best regards,

Ilya

This posting is provided "AS IS" with no warranties, and confers no rights.

--------------------
> From: "Jeremy" <jezonline@xxxxxxxxxxx>
> References: <umEpDi8OFHA.3880@xxxxxxxxxxxxxxxxxxxx>
<64$0lp9OFHA.1564@xxxxxxxxxxxxxxxxxxxxx>
<#t8wc#BPFHA.1268@xxxxxxxxxxxxxxxxxxxx>
<tz30okGPFHA.920@xxxxxxxxxxxxxxxxxxxxx>
<eTuV9uUPFHA.2568@xxxxxxxxxxxxxxxxxxxx>
<SN73xxVPFHA.920@xxxxxxxxxxxxxxxxxxxxx>
> Subject: Re: To cast or not to cast?
> Date: Sun, 10 Apr 2005 01:46:03 +0100
> Lines: 240
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microsoft.public.dotnet.framework.compactframework:26658
> X-Tomcat-NG: microsoft.public.dotnet.framework.compactframework
>
> Okay, so I used the 1040 length, it doesn't seem to complain, which is
good
> news I guess. To make sure it stores the data correctly I'm trying to
> retrieve it and feed it back to the biometric template matching method.
>
> Because it takes IntPtr's for BiometricData and Signature, I tried
creating
> new pointers and marshal copy the content that I retrieved earlier into
> these pointers. I failed. I tried the following:
>
> System.IntPtr BiometricDataPtr;//create new pointer
> BiometricData = (byte[])bioData[8];//BiometricData is an array of type
byte
> Marshal.Copy(BiometricData, 0, BiometricDataPtr, 1040);//copy content of
> BiometricData in an IntPtr
>
> "Use of unassigned local variable 'BiometricDataPtr'."
> Obvsiously it's unused, it's meant to point to something... what am I
> missing here?
>
> ""Ilya Tumanov [MS]"" <ilyatum@xxxxxxxxxxxxxxxxxxxx> wrote in message
> news:SN73xxVPFHA.920@xxxxxxxxxxxxxxxxxxxxxxxx
> > You should not guess the length, you should know it. It might be fixed
or
> > native code could return it somehow.
> > Most likely you're correct and FirstBIRSample.Length contains this size.
> > You should check out the documentation for the function you're calling
to
> > make sure it's correct.
> >
> > If value of a pointer is 0, it's null pointer. It means this pointer is
> not
> > valid and points to nothing.
> > Since no data is available, you could store it as DBNull.
> >
> > Best regards,
> >
> > Ilya
> >
> > This posting is provided "AS IS" with no warranties, and confers no
> rights.
> >
> > --------------------
> > > From: "Jeremy" <jezonline@xxxxxxxxxxx>
> > > References: <umEpDi8OFHA.3880@xxxxxxxxxxxxxxxxxxxx>
> > <64$0lp9OFHA.1564@xxxxxxxxxxxxxxxxxxxxx>
> > <#t8wc#BPFHA.1268@xxxxxxxxxxxxxxxxxxxx>
> > <tz30okGPFHA.920@xxxxxxxxxxxxxxxxxxxxx>
> > > Subject: Re: To cast or not to cast?
> > > Date: Sat, 9 Apr 2005 22:32:29 +0100
> > > Lines: 159
> > > X-Priority: 3
> > > X-MSMail-Priority: Normal
> > > X-Newsreader: Microsoft Outlook Express 6.00.2800.1478
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> > > Newsgroups: microsoft.public.dotnet.framework.compactframework
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> > > Xref: TK2MSFTNGXA01.phx.gbl
> > microsoft.public.dotnet.framework.compactframework:26653
> > > X-Tomcat-NG: microsoft.public.dotnet.framework.compactframework
> > >
> > > Thanks a lot for that! Before going to the UInt16 problem, I better
try
> to
> > > solve that IntPtr problem.
> > >
> > > Managed to use Marshal.Copy. Not sure how I should 'guess' the length
of
> > the
> > > Byte array to copy to. When I type FirstBIRSample.BiometricData (which
> is
> > > the IntPtr) in the command window, it returns to me: 2372256 - is this
> the
> > > size?
> > > I 'assumed' the size would be 1040 (which is stored in
> > > FirstBIRSample.Length).
> > >
> > > Second Part: Seems like the FirstBIRSample.Signature (also a pointer)
is
> > 0,
> > > how should I store this?
> > >
> > > Thanks so much!
> > >
> > > ""Ilya Tumanov [MS]"" <ilyatum@xxxxxxxxxxxxxxxxxxxx> wrote in message
> > > news:tz30okGPFHA.920@xxxxxxxxxxxxxxxxxxxxxxxx
> > > > While storing UInt16 as Int is OK, it will take more space. The
> problem
> > > > you're having is caused by range check. You might consider using
> > > > unchecked() to disable it.
> > > >
> > > > System.Runtime.InteropServices.Marshal class allows you to copy data
> > from
> > > > the pointer to the array. Look into Copy() methods of that class.
> > > >
> > > > Best regards,
> > > >
> > > > Ilya
> > > >
> > > > This posting is provided "AS IS" with no warranties, and confers no
> > > rights.
> > > > --------------------
> > > > > From: "Jeremy" <jezonline@xxxxxxxxxxx>
> > > > > References: <umEpDi8OFHA.3880@xxxxxxxxxxxxxxxxxxxx>
> > > > <64$0lp9OFHA.1564@xxxxxxxxxxxxxxxxxxxxx>
> > > > > Subject: Re: To cast or not to cast?
> > > > > Date: Fri, 8 Apr 2005 10:44:39 +0100
> > > > > Lines: 91
> > > > > X-Priority: 3
> > > > > X-MSMail-Priority: Normal
> > > > > X-Newsreader: Microsoft Outlook Express 6.00.2800.1478
> > > > > X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1478
> > > > > Message-ID: <#t8wc#BPFHA.1268@xxxxxxxxxxxxxxxxxxxx>
> > > > > Newsgroups: microsoft.public.dotnet.framework.compactframework
> > > > > NNTP-Posting-Host: host-84-9-101-26.bulldogdsl.com 84.9.101.26
> > > > > Path:
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> > > > > Xref: TK2MSFTNGXA01.phx.gbl
> > > > microsoft.public.dotnet.framework.compactframework:26572
> > > > > X-Tomcat-NG: microsoft.public.dotnet.framework.compactframework
> > > > >
> > > > > Thanks so much for the replies Alex and Ilya!
> > > > >
> > > > > I changed the types in sql. It wasn't happy with Uint16 mapped to
> > > smallint
> > > > > (sql says value is either too small or too large), so I just went
> for
> > an
> > > > > int.
> > > > >
> > > > > Not sure how to retrieve the data data an IntPtr is pointing to
> > though.
> > > > How
> > > > > can I get that data as a byte array?
> > > > >
> > > > > thanks so much again!
> > > > >
> > > > > ""Ilya Tumanov [MS]"" <ilyatum@xxxxxxxxxxxxxxxxxxxx> wrote in
> message
> > > > > news:64$0lp9OFHA.1564@xxxxxxxxxxxxxxxxxxxxxxxx
> > > > > >
> > > > >
> > > >
> > >
> >
>
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/
> > > > > > frlrfsystemdatasqldbtypeclasstopic.asp
> > > > > >
> > > > > > UInt32: Int will do. Signed and Unsigned integers are actually
the
> > > same;
> > > > > > just cast them to the right type.
> > > > > > UInt16: SmallInt, see warning above
> > > > > > Byte: TinyInt
> > > > > > BioAPI_*: look up underlying type definition and use it. Enums
are
> > > Int32
> > > > > by
> > > > > > default.
> > > > > > IntPtr: it's Int32, so store it as Int.
> > > > > >
> > > > > > Note, however, it's probably pointless to store pointers in the
> data
> > > > base.
> > > > > > Pointer itself is not important, most likely you need to store
> > > whatever
> > > > > > it's pointing to.
> > > > > >
> > > > > > Best regards,
> > > > > >
> > > > > > Ilya
> > > > > >
> > > > > > This posting is provided "AS IS" with no warranties, and confers
> no
> > > > > rights.
> > > > > >
> > > > > > --------------------
> > > > > > > From: "Jeremy" <jezonline@xxxxxxxxxxx>
> > > > > > > Subject: To cast or not to cast?
> > > > > > > Date: Fri, 8 Apr 2005 00:21:17 +0100
> > > > > > > Lines: 25
> > > > > > > X-Priority: 3
> > > > > > > X-MSMail-Priority: Normal
> > > > > > > X-Newsreader: Microsoft Outlook Express 6.00.2800.1478
> > > > > > > X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1478
> > > > > > > Message-ID: <umEpDi8OFHA.3880@xxxxxxxxxxxxxxxxxxxx>
> > > > > > > Newsgroups: microsoft.public.dotnet.framework.compactframework
> > > > > > > NNTP-Posting-Host: host-84-9-101-26.bulldogdsl.com 84.9.101.26
> > > > > > > Path:
> > > TK2MSFTNGXA01.phx.gbl!TK2MSFTNGP08.phx.gbl!tk2msftngp13.phx.gbl
> > > > > > > Xref: TK2MSFTNGXA01.phx.gbl
> > > > > > microsoft.public.dotnet.framework.compactframework:26546
> > > > > > > X-Tomcat-NG:
microsoft.public.dotnet.framework.compactframework
> > > > > > >
> > > > > > > Hi,
> > > > > > >
> > > > > > > I'm trying to convert the following types into types that I
can
> > > insert
> > > > > in
> > > > > > an
> > > > > > > SQL database (via a webservice). None of these however are
> > accepted
> > > by
> > > > > Sql
> > > > > > > (i.e., there is no OleDbType for them). I could only use
integer
> > > type
> > > > > for
> > > > > > > UInt32, that's about it. I'm totally unsure about the other
> types.
> > > > What
> > > > > > I've
> > > > > > > tried doing so far is casting them prior to sending them to
the
> > > > > > webservice.
> > > > > > > When inserting them I get errors though. Would anyone
know/could
> > > point
> > > > > me
> > > > > > to
> > > > > > > types that I could use? Any help would be really appreciated,
> i'm
> > > > lost!
> > > > > > >
> > > > > > > Thanks so much!
> > > > > > >
> > > > > > >
> > > > > > > System.UInt32 Length;
> > > > > > > System.Byte HeaderVersion;
> > > > > > > BioAPI_BIR_DATA_TYPE Type;
> > > > > > > System.UInt16 FormatOwner;
> > > > > > > System.UInt16 FormatID;
> > > > > > > System.Byte Quality; /*INT8 BioAPI_QUALITY*/
> > > > > > > BioAPI_BIR_PURPOSE Purpose;
> > > > > > > BioAPI_BIR_AUTH_FACTORS FactorsMask;
> > > > > > > System.IntPtr BiometricData;
> > > > > > > System.IntPtr Signature;
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > > >
> > > > >
> > > >
> > >
> > >
> > >
> >
>
>
>

.

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