VB/C Array parameters

I have a function in C, that has already been written by other People and
now I have to write a .dll with this function, so that I can call it from
the VB 6.0.
The C-function declaration is as follows:

---- C-Part----
-------------------------------------


void _stdcall mw_CaeMatinfo(mw_MatInfoTyp *pMatTblToCheck[], unsigned AnzMatToCheck,
mw_MatInfoTyp **pMatInfo[], unsigned *AnzMat, mw_ReturnTyp *Ret);

and the structures in C are:

#define MaxSearch 30
#define MaxResults 200

#define ReturnTypTypeLength 2
#define ReturnTypIdLength 21
#define ReturnTypMessageLength 221
#define ReturnTypLogNoLength 21
#define ReturnTypLogMsgNoLength 7
#define ReturnTypMessageV1Length 51
#define ReturnTypMessageV2Length 51
#define ReturnTypMessageV3Length 51
#define ReturnTypMessageV4Length 51
#define ReturnTypRFC_KeyLength 33
#define ReturnTypRFC_MessageLength 513

#define MatInfoTypMatnrLength 30
#define MatInfoTypWerkLength 30
#define MatInfoTypMaktxLength 70
#define MatInfoTypValueMentorCLength 31
#define MatInfoTypValueVisulaC1Length 31
#define MatInfoTypValueVisulaC2Length 31
#define MatInfoTypStatusLength 41
#define MatInfoTypExistenzkzLength 2
#define MatInfoTypMessageTypeLength 2
#define MatInfoTypMessageIdLength 21
#define MatInfoTypMessageLength 221
#define MatInfoTypMessageV1Length 51
#define MatInfoTypMessageV2Length 51
#define MatInfoTypMessageV3Length 51
#define MatInfoTypMessageV4Length 51


typedef struct
{
char Type[ReturnTypTypeLength];
char Id[ReturnTypIdLength];
unsigned Number;
char Message[ReturnTypMessageLength];
char LogNo[ReturnTypLogNoLength];
char LogMsgNo[ReturnTypLogMsgNoLength];
char MessageV1[ReturnTypMessageV1Length];
char MessageV2[ReturnTypMessageV2Length];
char MessageV3[ReturnTypMessageV3Length];
char MessageV4[ReturnTypMessageV4Length];
char RFC_Key[ReturnTypRFC_KeyLength];
char RFC_Message[ReturnTypRFC_MessageLength];
} mw_ReturnTyp;

typedef struct
{
unsigned Lfdnr;
char Matnr[MatInfoTypMatnrLength];
char Werk[MatInfoTypWerkLength];
char Maktx[MatInfoTypMaktxLength];
char ValueMentorC[MatInfoTypValueMentorCLength];
double ValueF;
char ValueVisulaC1[MatInfoTypValueVisulaC1Length];
char ValueVisulaC2[MatInfoTypValueVisulaC2Length];
char Status[MatInfoTypStatusLength];
char Existenzkz[MatInfoTypExistenzkzLength];
char MessageType[MatInfoTypMessageTypeLength];
char MessageId[MatInfoTypMessageIdLength];
unsigned MessageNumber;
char Message[MatInfoTypMessageLength];
char MessageV1[MatInfoTypMessageV1Length];
char MessageV2[MatInfoTypMessageV2Length];
char MessageV3[MatInfoTypMessageV3Length];
char MessageV4[MatInfoTypMessageV4Length];
} mw_MatInfoTyp;

Here is my program:
-------------------------------
VB-Part

---- Module1.bas----

Option Explicit

Const ReturnTypTypeLength = 2
Const ReturnTypIdLength = 21
Const ReturnTypMessageLength = 221
Const ReturnTypLogNoLength = 21
Const ReturnTypLogMsgNoLength = 7
Const ReturnTypMessageV1Length = 51
Const ReturnTypMessageV2Length = 51
Const ReturnTypMessageV3Length = 51
Const ReturnTypMessageV4Length = 51
Const ReturnTypRFC_KeyLength = 33
Const ReturnTypRFC_MessageLength = 513


Const MatInfoTypMatnrLength = 30
Const MatInfoTypWerkLength = 30
Const MatInfoTypMaktxLength = 70
Const MatInfoTypValueMentorCLength = 31
Const MatInfoTypValueVisulaC1Length = 31
Const MatInfoTypValueVisulaC2Length = 31
Const MatInfoTypStatusLength = 41
Const MatInfoTypExistenzkzLength = 2
Const MatInfoTypMessageTypeLength = 2
Const MatInfoTypMessageIdLength = 21
Const MatInfoTypMessageLength = 221
Const MatInfoTypMessageV1Length = 51
Const MatInfoTypMessageV2Length = 51
Const MatInfoTypMessageV3Length = 51
Const MatInfoTypMessageV4Length = 51

Public Type mw_ReturnTyp
Type As String * ReturnTypTypeLength
Id As String * ReturnTypIdLength
Number As Long
Message As String * ReturnTypMessageLength
LogNo As String * ReturnTypLogNoLength
LogMsgNo As String * ReturnTypLogMsgNoLength
MessageV1 As String * ReturnTypMessageV1Length
MessageV2 As String * ReturnTypMessageV2Length
MessageV3 As String * ReturnTypMessageV3Length
MessageV4 As String * ReturnTypMessageV4Length
RFC_Key As String * ReturnTypRFC_KeyLength
RFC_Message As String * ReturnTypRFC_MessageLength
End Type

Public Type mw_MatInfoTyp
Lfdnr As Long
Matnr As String
Werk As String
Maktx As String
ValueMentorC As String
ValueF As Double
ValueVisulaC1 As String
ValueVisulaC2 As String
Status As String
Existenzkz As String
MessageType As String
MessageId As String
MessageNumber As Long
Message As String
MessageV1 As String
MessageV2 As String
MessageV3 As String
MessageV4 As String
End Type

Declare Sub mw_CaeMatinfo Lib "ex21c.dll" (pMatTblToCheck() As mw_MatInfoTyp,
ByVal AnzMatToCheck As Integer, pMatInfo() As mw_MatInfoTyp, AnzMat As Integer,
Ret As mw_ReturnTyp)

(????) I don't know, if that is right. Anyway I had no idea how I should
declare the double pointer to pMatInfo[] (**pMatInfo[]).

---- form1.frm ----

Option Explicit

Const MaxSearch = 30
Const MaxResults = 200

Dim IndexMat As Integer
Dim IndexWerk As Integer
Dim pMatTblToCheck(MaxSearch) As mw_MatInfoTyp
Dim AnzMatToCheck As Integer
Dim pMatInfo(MaxResults) As mw_MatInfoTyp
Dim AnzMat As Integer
Dim Ret As mw_ReturnTyp

Private Sub cmbInMat_Click()
IndexMat = cmbInMat.ListIndex
End Sub

Private Sub cmdSearch_Click()
Dim n
For n = 0 To cmbInMat.ListCount - 1
pMatTblToCheck(n).Matnr = cmbInMat.List(n)
pMatTblToCheck(n).Werk = cmbInWerk.List(n)
Next
AnzMatToCheck = cmbInMat.ListCount
mw_CaeMatinfo pMatTblToCheck(), AnzMatToCheck, pMatInfo(), AnzMat, Ret
For n = 0 To AnzMat - 1
cmbOutMat.List(n) = pMatInfo(n).Matnr
cmbOutWerk.List(n) = pMatInfo(n).Werk
Next
End Sub

------------------------------------------------

I have also tried another things just as a test, to see if I could pass an
array of structures to a function in a .dll:

---- C-header test2.h ----

#define FirstNameLength 15
#define MiddleNameLength 12
#define LastNameLength 20

typedef struct
{
char FirstName[FirstNameLength];
char MiddleName[MiddleNameLength];
char LastName[LastNameLength];
}customer;

void _stdcall mult(customer A[], customer B[]);

---- C-programm test2.C ----

#include <windows.h>
#include <stdio.h>
#include "test2.h"

void _stdcall mult(customer A[], customer B[])
{
int i,j;

for(j=0; j<51; j++)
{
for(i=0; i<FirstNameLength; i++)
B[j].FirstName[i] = A[j].FirstName[i];
for(i=0; i<MiddleNameLength; i++)
B[j].MiddleName[i] = A[j].MiddleName[i];
for(i=0; i<LastNameLength; i++)
B[j].LastName[i] = A[j].LastName[i];
};
}

BOOL WINAPI DllMain (HINSTANCE hDLL, DWORD dwReason, LPVOID lpReserved)
{
return TRUE;
}

---- VB - Modules1.bas ----

Option Explicit
Declare Sub mult Lib "test2.dll" (A() As Customer, B() As Customer)
Const FirstNameLength = 15
Const MiddleNameLength = 12
Const LastNameLength = 20
Public Type Customer
FirstName As String * FirstNameLength
MiddleName As String * MiddleNameLength
LastName As String * LastNameLength
End Type
Global x() As Customer, y() As Customer

---- VB - Form1.frm ---

Private Sub Command1_Click()
Dim i As Integer
ReDim x(50)
ReDim y(50)
For i = 0 To 10
x(i).FirstName = Text1.Text
x(i).MiddleName = Text2.Text
x(i).LastName = Text3.Text
Next
'I have also called the function with different input values in
each structure
mult x(), y()
End Sub

---------------------------------------

That has worked. With the debug, I can see that I got the right results,
at least when the array is small (size about 50). But when I close the VB-program
(when I'm using the VB-debug or running the executable file), an error ocurrs
(unallowed memory handling, or something like that - my Windows is not in
english -) and the program or the VB-studio shuts down.
When I use bigger arrays, the same error occurs already when call the function.
Then when I change:

void _stdcall mult(customer A[], customer B[]);

for :

void _stdcall mult(customer *A[], customer *B[]);

, because that is what I need in my program, that the same error occurs already
when call the function.

Is there any way of passing pointers of arrays of structures from the VB
to a function in a .dll wrutten in C????

I would appreciate your help. Thanks in advance

Best Regards,

Gastao Woelfert