[RESOLVED] Conversion of C Function to VB Function

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?

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...

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

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:

Code:

---

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

Dim arrNames(20) as Name

---

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:

Code:

---

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.