LPSTR -> String : Type Incompatibility Issue

[Michael Chong]

Another same issue on "NullReferenceException" :-
I have an (exe) executable program created in VB.NET 2003 that calls to a
MFC DLL written in VC++.NET 2003. I always get an error msg
"NullReferenceException: Object Reference Not Set to an Instance of an
Object" when my exe calls the following codes:

in VB.NET

Declare Function test Lib "C:\Cyob\IOComm\Debug\IOComm.dll" _
(ByVal a As Long, ByRef b As String) As Integer

Dim did As Integer
Dim ret As Integer

ret = test(PortHnd, did) //ERROR: Object Reference Not Set to an
Instance of an Object


in VC++.NET

extern "C" int APIENTRY test(HANDLE a, LPSTR b)
{
strcpy(b, "hello"); //ERROR: Object Reference Not Set to an
Instance of an Object
return 99;
}


Why is this happening? Any idea in solving such matter?
Thanks in Advance

Michael.

 

[Michael Chong]

Sorry, the "Dim did as Integer" should be "Dim did as String"
I believe is DataType issue from VC++.NET (LPSTR) pass to VB.NET (String)

When I try to replace String with IntPtr, it doesn't give me error but the
return value for "did variable" is some numbers.
Plz help! TQ

 

[Wild Wind]

Michael,

It looks like you haven't allocated memory to copy the
"hello" to in your strcpy call.

Try putting

b = new CHAR[strlen("hello") + 1];

before your call to strcpy.