RE: [Mingw-users] [mingw - StupidTechiQuestions] VB 6.0 and MinGW custom DLL

[<pau...@wi...>]

Hi V.R.Anand and Reg:
  I tried your example V.R. Anand and I am having some proplems with it.  Fist I will state my code, and from there explain the reasons for my changes.

----cvtup.cpp-----
 #include <string.h>
 #if BUILDING_DLL
 # define DLLIMPORT __declspec (dllexport)
 #else /* Not BUILDING_DLL */
 # define DLLIMPORT __declspec (dllimport)
 #endif /* Not BUILDING_DLL */
 /*Trivial code to convert an input string to upper case.
 Intended to demonstrate interfacing a MINGW C DLL with MS Excel through
 a VBA macro. */
 DLLIMPORT int cvtup(char *str) {
 	int i=0;
 	for(i=0; i< strlen(str); i++){
		if((str + i) >= "a" && (str + i ) <= "z"){
 			str[i] += "A" - "a";
 		}
 	}
 	return strlen(str);
 }
----end of cvtup.cpp----

----vb code ---
 ' Retrive Function
 Private Declare Function cvtup Lib "C:\Documents and Settings\Admin\My Documents\Com-MinGW\VbStringConverter\cvtup.dll" _
    (ByRef Bstr As Byte) As Long
 
Private Sub cmdEnter_Click()

Dim Str As String, Bstr() As Byte, L As Long
' Get input text
Str = Me.txtIN.Text

' Calculate the size of string
L = Len(Str)

' Allocate memory to byte array to hold the string.
' Allocate L+1 bytes to allow for terminal null character for C string.
ReDim Bstr(1 To L + 1)

 ' Copy string bytes to byte array.
 For I = 1 To L
     Bstr(I) = Asc(Mid(Str, I, 1))
 Next I
 
  Bstr(L + 1) = 0     ' terminal null byte for C string
' Call the function in the MinGW DLL

L = cvtup(Bstr(1))

Str = ""        ' initialize output string

' Copy bytes from function output back to VB string
 For I = 1 To L
   Str = Str + Chr(Bstr(I))
 Next I
 
 ' Display output
 
 Me.txtOUT.Locked = False
 Me.txtOUT.Text = Str
 Me.txtOUT.Locked = True
 
End Sub

----End VB code--------
When I first read your post I wanted to try and compile it in c++.  So using the example in the cvtup.c file.  I compile it as a c++ app using the following command

mingw32-g++ -c  -DBUILDING_DLL=1 -mrtd -g -O2 -o cvtup.o cvtup.c

And scored a wired error, not shure why.  But for some reason the ISO standord dose not allow str[i] in an if statment. ( I compile it on borland and VC++ and recived the same complant ) It will allow for (str + i) instead. That was the only real change  I made to the file. recompile it and used the following for the dllwarp 

dllwrap -s --export-all --output-def cvtup.def --driver-name mingw32-g++ -o cvtup.dll cvtup.o

And it worked.  As expected.

Next I proceded to make a simple form in VB6  Two text boxes, txtIN and txtOUT.  For inputting and outputting the results, respective to var names.  Also a command button to take action.

In the example when you declared your function by default as Public.  VB when compling the could state that it should be private so i make the change. VB was happy.  So I proceded to run the app in debug mode.  When it arived to the line: L = cvtup(Bstr(1)).  It buged out with a statment of:

Run-time error '453':

Can't find DLL entry point cvtup in C:\Documents and Settings\Admin\My Documents\Com-MinGW\VbStringConverter\cvtup.dll