VarPtr

VarPtr

• Sajeesh

  http://www.google.com.au/search hl=en&safe=off&q=varptr+.net&meta=

  More specifically

  http://www.codeproject.com/vb/net/singleinstance.asp

  has this:

  
  <P>There are two operations required - set the <CODE lang=vbnet>lpData</CODE>
  member to point to a <CODE lang=vbnet>String</CODE>, and retrieve a <CODE lang=vbnet>String</CODE> from it. In VB6, you would use <CODE
  lang=vb>VarPtr</CODE> and the <CODE lang=vbnet>RtlMoveMemory</CODE> API (a.k.a.
  <CODE lang=vbnet>CopyMemory</CODE>) to do this. In .Net, <CODE
  lang=vbnet>VarPtr</CODE> no longer exists, but the <CODE
  lang=vbnet>Marshal</CODE> class provides much better alternatives.</P>
  <P>To set the pointer to the value of a <CODE lang=vbnet>String</CODE>:</P><PRE lang=vbnet>'//Get an array of bytes for the string
  Dim B() As Byte = Encoding.Default.GetBytes(StringVarToSend)
  
  Try
  '//Allocate enough memory on the global heap
  Dim lpB As IntPtr = Marshal.AllocHGlobal(B.Length)
  
  '//Copy the managed array to the un-managed pointer
  Marshal.Copy(B, 0, lpB, B.Length)
  
  Dim CD As COPYDATASTRUCT
  With CD
  .dwData = 0
  .cbData = B.Length
  
  '//The ToInt32 function converts an IntPtr to an Integer pointer
  .lpData = lpB.ToInt32
  End With
  
  'Do something with CD here...
  
  Finally
  '//Clean up
  Erase B
  Marshal.FreeHGlobal(lpB)
  End Try
  </PRE>
  <P>To retrieve a <CODE lang=vbnet>String</CODE>
  from the pointer:</P><PRE lang=vbnet>Dim B() As Byte
  Try
  '//Get the COPYDATASTRUCT from the message
  Dim CD As COPYDATASTRUCT = m.GetLParam(GetType(COPYDATASTRUCT))
  
  '//Allocate enough space in B
  ReDim B(CD.cbData)
  
  '//Create an IntPtr from the Integer pointer
  Dim lpData As IntPtr = New IntPtr(CD.lpData)
  
  '//Copy the data into the array
  Marshal.Copy(lpData, B, 0, CD.cbData)
  
  '//Get the string from the Byte Array
  Dim strData As String = Encoding.Default.GetString(B)
  
  '//Do something with the String here...
  
  Finally
  '//Clean up
  Erase B
  End Try
  </PRE>

  
  
  
• VarPtr