casting BSTR as char* in a dll; different results depnding on VB/C# caller.
- by Toby Wilson
I have a dll function that takes BSTR parameters. These are casted as char* before being used for other things.
When the dll is called from VB code this works fine. However, when it is called from C# code, only the first character is pointed to.
Both of these are excel addIns for Pre-2007 and 2007+ versions of Office, which call into a faster C++ AddIn. They actually call it directly, not through Excel.
The VB function declaration looks like this:
Private Declare Function Test Lib "ExcelAddIn.xll" (ByVal param As String) As String
The C# function declaration looks like this:
[DllImport("ExcelAddIn.xll", CharSet=CharSet.Ansi)]
[return:MarshalAs(UnmanagedType.BStr)]
private static extern string Test([MarshalAs(UnmanagedType.BStr)] string param);
When debugging the dll and watching the input BSTR values, they appear to be correct from both; just the C# one only casts the first character.
Charset=CharSet.Unicode makes no difference.
Any ideas anyone?
