Problem calling unmanaged API from C#, works from VB.NET

Hello!
I have a .NET application that communicates with an AS400 application
through PCOM. I call an unmanaged function in the PCOM API to get a
string back representing the screen in the host system. When I call
this function from VB.NET it works fine but from C# I only get a
string containing unreadable characters back. If anyone knows what's
wrong I'd be very happy!

VB.NET code that works:
Private Declare Function hllapi Lib "PCSHLL32.D LL" (ByRef Func As
Integer, ByVal DataString As String, ByRef Length As Integer, ByRef
RetC As Integer) As Integer

Dim testStr As New String(" ", 8000)
ret = hllapi(COPY_PRE SENTATION_SPACE , testStr, HllLength,
HllReturnCode)
ResponseBuffer = testStr

testStr is the variable that contains the string I am interested in.

C# code that does not work:
[DllImport("pcsh ll32.dll",Entry Point="hllapi", ExactSpelling=f alse,CharSet=Ch
arSet.Auto,SetL astError=true)] public static extern int hllapi(ref int Func,
[MarshalAs(Unman agedType.LPWStr )] string DataString, ref int Length,
ref int RetC);

string hllData = new string(' ', 8000);
int hllLength;
int hllReturnCode;
int ret;
hllLength = 0;
hllReturnCode = 0;
ret = hllapi(ref COPY_PRESENTATI ON_SPACE, hllData, ref hllLength, ref
hllReturnCode);

responseBuffer = hllData;

hllData either contains nothing or unreadable characters depending on
how I write DllImport. I have tried the following alternatives as
well:

[DllImport("pcsh ll32.dll",Entry Point="hllapi", ExactSpelling=f alse,CharSet=Ch
arSet.Unicode,S etLastError=tru e)] public static extern int hllapi(ref int Func,
[MarshalAs(Unman agedType.LPWStr )] string DataString, ref int Length,
ref int RetC);
[DllImport("pcsh ll32.dll",Entry Point="hllapi", ExactSpelling=f alse,CharSet=Ch
arSet.Unicode,S etLastError=tru e)] public static extern int hllapi(ref int Func, string DataString, ref
int Length, ref int RetC);

Regards
Ulrika

Ulrika,

The only difference between the VB.NET code and the C# code once
compiled is that the VB.NET code effectively has ExactSpelling=t rue,
and you have it set to false in the C# declaration. Does it work if
you change to ExactSpelling=t rue in the C# code?

Mattias

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

The C# declaration is also using ansi. I don't know what the VB declaration
defaults to if not specified.

The C# declaration is also using ansi. I don't know what the VB declarationdefaults to if not specified.

It defaults to Ansi.

Mattias

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