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Dave,
I don’t wish to relive the days of working with VB6/COM data types, BSTRs, fixed-form source, old Cray-style POINTER extension, and such like. Instead, I suggest an alternate approach where the Fortran code uses standard features for C interoperability and where the Visual Basic .NET code is kept fairly simple using the “Cdecl” calling convention. With such an approach, you use .NET StringBuilder class for string passing to and from Fortran as shown below:
Option Strict Off
Option Explicit On
Imports System.Text
Imports System.Runtime.InteropServices
Public Class frmHelloWorld
<UnmanagedFunctionPointer(CallingConvention.Cdecl)> _
Public Delegate Sub WriteDelegate(SomeString As StringBuilder, ByRef Irc As Integer)
<DllImport("HelloWorld_Fortran.DLL", CallingConvention:=CallingConvention.Cdecl)> _
Public Shared Sub HelloWorld_Fortran(MsgString As StringBuilder, _
<MarshalAs(UnmanagedType.FunctionPtr)> fPtr As WriteDelegate)
End Sub
Private Sub btnRun_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnRun.Click
Dim strMessage As StringBuilder
Dim IRC As Integer
strMessage = New StringBuilder("From VB.NET: Hello World")
Call RTBDisplayStatus(New StringBuilder("From VB.NET: Starting Fortran"), IRC)
Call HelloWorld_Fortran( _
strMessage, _
AddressOf RTBDisplayStatus)
Call RTBDisplayStatus(New StringBuilder("From VB.NET: Finished Fortran"), IRC)
End Sub
Public Sub RTBDisplayStatus(s1 As StringBuilder, ByRef irc As Integer)
'
'frmHelloWorld.vb / RTBDisplayStatus
'
RichTextBox1.Text += s1.ToString() & vbCrLf
System.Windows.Forms.Application.DoEvents()
'
End Sub
End Class
The Fortran code that interoperates with the above VB.NET class is Fortran 2003 standard compliant barring the !DEC$ ATTRIBUTES for DLLEXPORT: note the use of ISO_C_BINDING intrinsic module for binding the procedures and for interoperable data types. In addition, note the dummy argument for the string type is set up effectively as a character array of length 1 since strings in C are better viewed as a char array or a pointer to a char array. Also, you will notice this argument is null-terminated. These are all standard aspects of modern Fortran interoperability with C or a companion processor that is C-like which is what P/Invoke interoperability layer in ,NET becomes when "Cdecl" calling convention is used and marshaling is done as above in the Visual Basic setup.
MODULE FortranDll USE, INTRINSIC :: ISO_C_BINDING, ONLY : C_CHAR, C_NULL_CHAR, C_INT IMPLICIT NONE PROCEDURE(VBWriteWindowInterface), POINTER :: VBWriteWindow ABSTRACT INTERFACE SUBROUTINE VBWriteWindowInterface(SomeString, ErrorCode) BIND(C) IMPORT :: C_CHAR, C_INT CHARACTER(KIND=C_CHAR,LEN=1), INTENT(INOUT) :: SomeString(*) INTEGER(C_INT), INTENT(INOUT) :: ErrorCode END SUBROUTINE VBWriteWindowInterface END INTERFACE CONTAINS !DEC$ ATTRIBUTES DLLEXPORT::HelloWorld_Fortran SUBROUTINE HelloWorld_Fortran( InputString, fPtr_VBWriteWindow ) BIND(C, NAME="HelloWorld_Fortran") !.. Argument list CHARACTER(KIND=C_CHAR,LEN=1), INTENT(INOUT) :: InputString(*) PROCEDURE(VBWriteWindowInterface) :: fPtr_VBWriteWindow !.. Local variables CHARACTER(KIND=C_CHAR,LEN=1), ALLOCATABLE :: OutString(:) !.. Work char array CHARACTER(KIND=C_CHAR,LEN=:), ALLOCATABLE :: TempString !.. Work Fortran string INTEGER(KIND=C_INT) :: Irc INTEGER :: StringLen INTEGER :: Istat INTEGER :: I !.. Set the procedure pointer VBWriteWindow => fPtr_VBWriteWindow ! Create our message, and pass both it and the return code to VbWriteWindow TempString = 'From Fortran: Hello World' StringLen = LEN_TRIM(TempString) !.. Allocate the work char array to StringLen+1 for null-termination ALLOCATE( CHARACTER(KIND=C_CHAR,LEN=1) :: OutString(StringLen+1), STAT=Istat) IF (Istat /= 0) THEN RETURN END IF !.. Copy string FORALL (I = 1:StringLen) OutString(I)(1:1) = TempString(I:I) END FORALL OutString(StringLen+1)(1:1) = C_NULL_CHAR !.. Null terminate Irc = 0 CALL VBWriteWindow( OutString, Irc) !.. Clear the work areas for second message DEALLOCATE(TempString, STAT=Istat) IF (Istat /= 0) THEN RETURN END IF DEALLOCATE(OutString, STAT=Istat) IF (Istat /= 0) THEN RETURN END IF !.. Determine input string length; check for null-termination StringLen = 0 Loop_SizeVec: DO ! IF (InputString(StringLen+1) == C_NULL_CHAR) THEN EXIT Loop_SizeVec END IF StringLen = StringLen + 1 IF (StringLen == 2048) THEN !.. Replace: arbitrary large length EXIT Loop_SizeVec END IF END DO Loop_SizeVec IF (StringLen == 0) RETURN ALLOCATE( CHARACTER(KIND=C_CHAR,LEN=StringLen) :: TempString, STAT=Istat) IF (Istat /= 0) THEN RETURN END IF !.. Copy string FORALL (I = 1:StringLen) TempString(I:I) = InputString(I)(1:1) END FORALL ! ! Create our message, and pass both it and the return code to VbWriteWindow1 TempString = 'Through Fortran: ' // TempString StringLen = LEN_TRIM(TempString) ALLOCATE( CHARACTER(KIND=C_CHAR,LEN=1) :: OutString(StringLen+1), STAT=Istat) IF (Istat /= 0) THEN RETURN END IF !.. Copy string FORALL (I = 1:StringLen) OutString(I)(1:1) = TempString(I:I) END FORALL OutString(StringLen+1)(1:1) = C_NULL_CHAR !.. Null terminate Irc = 0 CALL VBWriteWindow( OutString, Irc) !.. RETURN END SUBROUTINE HelloWorld_Fortran END MODULE FortranDll
I've also attached the zip file of the Visual Studio 2012 solution. When you run this, you should get results as shown below and no heap corruption issues.
I find this approach a lot cleaner and simpler to work with. But if you prefer the old style, then I'll leave it to one of the more patient readers who will have a fix your problem (perhaps a simple tweak in your original VB code to ByRef vs ByVal).
Hope this helps,
