[RESOLVED] Conversion of C Function to VB Function

[amolt]

Hi All,

I had one declaration from a dll built in C as:

typedef struct
{
char sName[10];
}NAME;

NAME arrNames[20];
==================================================
Function declaration:
long FindNames(long Records, NAME *rNames)

After calling this function by passing the array pointer to arrNames
it fills up the arrNames.
==================================================

The converted function declaration in VB as follows:

Dim arrNames(20) as String

Declare Function FindNames(ByVal Records as Long,ByRef rNames() as String) As Long

But when I called this function the application gets crash, I suppose the conversion is not proper and thats why I am not getting expected result.


Can someone help me out to get rid from this problem?

[randem]

It would help to post your code you are using in the function and how you are calling it. You leave EVERYTHING open to speculation...

[amolt]

Hi Randem,

As I use third party Dll I have only the function definations
and the declaration for the function FindNames in C is as bellow:
typedef struct
{
char sName[10];
}NAME;

NAME arrNames[20];
==================================================
Function declaration from a worker dll:
long FindNames(long Records, NAME *rNames)


After calling this function by passing the array pointer to arrNames
it fills up the arrNames.
==================================================

I converted the Definations of this function for VB6 and called in my
application as follows:

Dim arrNames(20) as String
Private Declare Function FindNames Lib "Worker.dll" _
(ByVal Records as Long,ByRef rNames() as String) As Long

Private Sub cmdGetNames_Click()
Dim retValue as long
'After calling the function application gets crashed with vb6 error
retValue=FindNames(10,arrNames())
'==================================================
'Add Returned Names to List Box
Dim iCnt as Integer
For iCnt = Lbound(arrNames) To Ubound(arrNames)
List1.AddItem arrNames(iCnt)
Next
End Sub

[randem]

Please post you code using the code tags to make it more readable...

The definition are not the same for your second parameter. You have a fixed length parameter for the C call and a variable length parameter for th eVB call. Are you sure the first parameter is passed ByVal and not ByRef?

You probably need something like this for the second parameter:

Private Type NAME
       sName(10) as Byte   ' or sName as String(10) I believe this will work
End Type

Dim arrNames(20) as Name

[ccoder]

There are several problems with your converted code.

Dim arrNames(20) as String actually creates an array of 21 (0 to 20) BSTRs, not strings. A BSTR is a 4-byte 'pointer' to a string that is located somewhere else in memory. Change the declaration to Dim arrNames(20) as String * 10 and the strings will actually reside in contiguous memory beginning at arrNames(0). arrNames will then look like a C string array.

In the C code, rNames is a pointer of type NAMES and a pointer is just a Long that contains the address of the variable that it is pointing to.

The declaration for Function FindNames is typical for many C functions in that there is an address (rNames) for some data type and a variable (Records) giving the number of occurances. You should be okay there as long as you don't pass anything greater than UBound(arrNames). However, the second parameter needs some work. I would try something like the following:

Declare Function FindNames(ByVal Records As Long, rNames As Any) As Long

Dim rNames As Long

rNames = VarPtr(arrNames(0))

retValue = FindNames(10, ByVal rNames)

I believe this should work. I'm not as familiar with the inner workings of VB as I am with C, so it's possible that I have missed something.