Write 'C' char array[] to VB array() As Char

Hi VB Experts

Is it possible for a 'C' function to use a pointer to a char array to write to a VB array As Char?

I have tried this but the C function only fills the first element in the VB array.

C Code:

Code:

---

EXPORT int __stdcall SocknetRecv (int nSocket, LPSTR *lpBuf, int nSize)
{
        int nRecv, nLen;
        LPTSTR lpPtr;

        for (nLen = nSize, lpPtr = *lpBuf; nLen > 0;)
        {
                nRecv = recv(nSocket, lpPtr, nLen, 0);
                if (nRecv <= 0)
                {
                        nResult = WSAGetLastError();
                        return nRecv;
                }

                lpPtr += nRecv;
                nLen -= nRecv;
        }

        nResult = 0;

        return nSize - nLen;
}

---

And in VB

Code:

---

Public Declare Function SocknetRecv Lib "SocknetLib.dll" (ByVal nSocket As Integer, ByRef Buffer() As Char, ByVal Size As Integer) As Integer

Dim RData(100) As Char
'Call it
nBytes = SocknetRecv(Socket, RData, RData.Length)

---

If anyone can help me with this i will be most grateful, I do not know VB very well

Looking forward to your replies

I don't sure but if you parameter is a pointer
you cant try something like :

Code:

---

SocknetRecv(Socket, RData(0), RData.Length)

---

where lpBuf and rData would be same memory address, then these are
going to have same values

Code:

---

SocknetRecv (int nSocket, LPSTR *lpBuf, int nSize)

---

First Dimming As Char wouldn't work, except if you had a userdefined type Char.
I'd go about like that:

Code:

---

Dim RData(100) as Byte
'then you declare the function like that:
Public Declare Function SocknetRecv Lib "SocknetLib.dll" (ByVal nSocket As Integer, ByRef Buffer As Byte, ByVal Size As Integer) As Integer
'and the call looks like that:
nBytes = SocknetRecv(Socket, RData(0), UBound(RData) + 1)

---

Explanation: Declaring the parameter ByRef Buffer as Byte makes VB to pass a pointer to the function which points to a byte.
But when calling the function you actually pass the first byte of the array RData(0) which passes the pointer to it, which is ALSO the pointer to the complete array, since it points to the first element. This is how C expects pointers to arrays.
I'm not sure what will be passed when declaring Buffer() as an array.

I have used the above method to pass an array of longs from and to a C function which worked well.

Come to think about it: "RData.Length" makes me think that you are using VB.Net and are possibly in the wrong forum.
The above method is definitely working with VB6, and I'm not sure if the declaration as described works in VB.Net, too, but I think it should.

Hi Wof

Thank you for your reply, sadly it didn't work, recv() failed with invalid pointer address.

I think i will have to replace

Code:

---

LPSTR *lpBuf

---

with a

Code:

---

SAFEARRAY *ppSafe

---

safe-array structure to pass arrays to and from the 'C' dll.

Well VB6 doesn't know about Pointers, so it might not be possible.

Could you please clarify if you are using VB6 or VB.Net? Because the method of producing a pointer to an array as I described it works allright under VB6.

Ah yes i do apologize it is VB.Net and also apologize for posting this in the wrong forum. I am a C programmer who is writing a dll for a friend to be used in a 'VB.Net' application. My knowledge on VB is limited.

Well, then you'd better repeat your question in the .Net forum.
I'm quite sure there is a proper way of declaring the parametrs that would work under VB.Net as well.
Although, I cannot think why it shouldn't work as I described...

Thanks you, will do