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win32 DLL and LPTSTR

Hi there.

Having a problem calling a win32 function from a dll.
Here is the function header:

DWORD thrdGetHcNum (DWORD nPort, DWORD nBaudrate, LPTSTR lpszHcNum)

//Description of the 3rd parameter
LpszHcNum: The head of the buffer area used to store the serial number
of the terminal, 9 bytes at least.

Here is my code:

[DllImport("comd ll.dll", SetLastError = true)]
public static extern uint thrdGetHcNum(in t nPort, int nBaudrate,
[MarshalAs(Unman agedType.LPTStr )] ref StringBuilder lpszHcNum);

//The actual call
StringBuilder Buffer = new StringBuilder(1 0);
result=thrdGetH cNum(Port,Baud, ref Buffer);

Everytime I runt his, I get a Object not set to reference error.
Can anyone tell me what I am doing wrong?
I have tried using a string, a char[] buf = new[10], MarshalAs.LPTst r
and MarshalAs.Array but always hit the same problem.

I am calling other functions from the dll without any problem. The only
difference with this one is I should be getting a string back with some
data in it.

Any help on this would be appreciated.



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Nov 16 '05 #1
1 5973
> [DllImport("comd ll.dll", SetLastError = true)]
public static extern uint thrdGetHcNum(in t nPort, int nBaudrate,
[MarshalAs(Unman agedType.LPTStr )] ref StringBuilder lpszHcNum);

I think that "ref" is not necessary here. Reference types are always passed
by reference. With "ref" you pass a reference to the reference.

[DllImport("comd ll.dll", SetLastError = true)]
public static extern uint thrdGetHcNum(in t nPort, int nBaudrate,
[MarshalAs(Unman agedType.LPTStr )] StringBuilder lpszHcNum);

I hope this will help
Regards, Wiktor Zychla
Nov 16 '05 #2

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