Exiting a DLL from Visual Basic

[jj2007]

The problem is ...., MasmBasic

Now we are getting somewhere...  :bg
Why don't you implement seh macros for MasmBasic and have "Open" routine raise an error(exception) instead of "MsgBox".

drizz,
Thanks for the SEH lesson, but the problem is not MasmBasic - Visual Basic is the problem. I want a "graceful crash" if there is a coding error, such as opening a non-existent file, or asking for an array element with a negative index. The solution attached above works perfectly - remember the return address in a global variable, and return to VB with a "wrong" edi value to trigger the runtime error. Before the VB error message, MasmBasic will show the real error, and clean up open handles etc.

[Marko]

I don't know if this could help you, but when I had to trap the result of a DLL function(wriiten in C ) in VB (via On error ...) I always used the structure HRESULT.

VB doesn't interpret HRESULT as a normal handle to a result but to a special automation type that says if a fucntion is successful or not.

Here there is a description of the structure :    http://www.maruf.ca/files/caadoc/CAASysQuickRefs/CAASysHRESULT.htm

After i declare an ODL file (automation description)  to create a type library. At this point you can declare the fucntions in Vb and errors are trappable with On error goto statement.

[jj2007]

Thanks, Marko. It seems that HRESULT is set by COM interfaces, pretty complex for my taste. A DLL in assember is typically a snippet meant to accelerate an innermost loop.

Anyway, the solution posted above works fine. What was really nasty was the sudden exit of MS Word. Now if there is a runtime error in the DLL, VB stops and displays a 'The DLL returned an error' message.

Code Select Expand

Sub ShowString()
    Dim JJ$, ErrDesc$
    WantError = 1
    On Error GoTo MyErr
    JJ$ = "Bad luck" + Space$(1000)  ' Loads \masm32\include\Windows.inc
    For n = 0 To 22271         ' with 22273 lines max, 7 secs/Mio
        GetString n, JJ$
    Next
    If WantError Then
        GetString2 123456, JJ$       ' Trigger an error
    Else
        GetString2 2, JJ$            ' Show line 2 (zero-based) of Windows.inc
    End If
    MsgBox JJ$, vbOK, "MasmBasic returned a string from Windows.inc:"
    Exit Sub
MyErr:
   ErrDesc$ = "Non-DLL error:"
   If Err.Number = 49 Then ErrDesc$ = "The DLL returned an error"
   MsgBox Err.Description, vbOK, ErrDesc$
End Sub