ptr to string ?

27 Feb 2006 9:13 AM

Delfim Da Costa

Hi,

I have some problems to use GetPrinterData Win32 API. in fact my problem is

: how can get the in a string a buffer known by it's ptr ?

Can anybody help me ?

Thanks,

Delfim.

this a part of my code :

<DllImport("winspool.Drv", CharSet:=CharSet.Ansi,
EntryPoint:="GetPrinterDataA", _
SetLastError:=True, ExactSpelling:=True, _
CallingConvention:=CallingConvention.StdCall)> _
Private Shared Function GetPrinterData( _
ByVal hPrinter As IntPtr, _
<MarshalAs(UnmanagedType.LPStr)> ByVal pValueName As String, _
ByRef pType As Integer, _
ByRef pData As IntPtr, _
ByVal nSize As Integer, _
ByRef pcbNeeded As Integer) As Integer
End Function

Public Function GetPrinterData(ByVal PrinterName As String, ByVal ValueName
As String) As Object
    Dim hPrinter As IntPtr
    Dim pData As IntPtr = IntPtr.Zero
    Dim cBuf As Integer
    Dim pcbNeeded As Integer
    Dim pType As Integer
    Dim ret As Integer
    Dim oData As Object

    hPrinter = OpenPrinter(PrinterName)
    ret = GetPrinterData(hPrinter, ValueName, pType, IntPtr.Zero, 0,
pcbNeeded)
    If pcbNeeded <= 0 Then
        Throw (New System.Exception("Unable to allocate memory"))
    End If

    pData = Marshal.AllocHGlobal(pcbNeeded)
    ret = GetPrinterData(hPrinter, ValueName, pType, pData, pcbNeeded, cBuf)
    If ret <> 0 Then
        Throw New Win32Exception(Marshal.GetLastWin32Error())
    End If

    Select Case pType
        Case REG_DWORD
            oData = pData.ToInt32

        Case REG_SZ
            oData = Marshal.PtrToStringAuto(pData)

        Case Else
            oData = pData
    End Select

    ClosePrinter(hPrinter)

    Return oData
End Function

27 Feb 2006 5:28 PM

Mattias Sjögren

>I have some problems to use GetPrinterData Win32 API. in fact my problem is
>: how can get the in a string a buffer known by it's ptr ?
>Can anybody help me ?

Since you're explicitly calling the ANSI version of the API I guess
you should use Marshal.PtrToStringAnsi (not Auto) to read the string.
And don't forget to free the memory allocated with AllocHGlobal.

Mattias

--
Mattias Sjögren [C# MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

1 Mar 2006 12:42 PM

Delfim Da Costa

I have tried this but it's not working.
I have made some debug session and maybe there is a problem in second call
to GetPrinterData, but i don't find what is it

Delfim.

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"Mattias Sjögren" <mattias.dont.want.spam@mvps.org> wrote in message
news:eqPoUO8OGHA.1216@TK2MSFTNGP14.phx.gbl...
> >I have some problems to use GetPrinterData Win32 API. in fact my problem
> >is
>>: how can get the in a string a buffer known by it's ptr ?
>>Can anybody help me ?
>
> Since you're explicitly calling the ANSI version of the API I guess
> you should use Marshal.PtrToStringAnsi (not Auto) to read the string.
> And don't forget to free the memory allocated with AllocHGlobal.
>
>
> Mattias
>
> --
> Mattias Sjögren [C# MVP] mattias @ mvps.org
> http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
> Please reply only to the newsgroup.

4 Mar 2006 12:37 PM

José_Manuel_Agüero

Hello Delfim,

Why don't you use a byte array as a buffer for the function call?:
<DllImport("winspool.Drv", CharSet:=CharSet.Ansi, _
EntryPoint:="GetPrinterDataA", _
SetLastError:=True, ExactSpelling:=True, _
CallingConvention:=CallingConvention.StdCall)> _
Private Shared Function GetPrinterData( _
ByVal hPrinter As IntPtr, _
ByVal pValueName As String, _
ByRef pType As Integer, _
[Out] ByVal pData() As Byte, _
ByVal nSize As Integer, _
ByRef pcbNeeded As Integer) As Integer
End Function

Now you have the bytes in an array, only need to use the bitconverter class to transform into a string or a numeric type.

Regards.

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