Bluetooth communication

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From: arthurclucas on 29 Apr 2008 10:27

---

Hi everyone,

I'm have two iPac Devices and I'm trying send some bytes from one to
another via Bluetooth communication.
I use the CreateFile command to send the data and the ReadFile command
to read the data.
In booth commands I use the appropriate COM port.
When I try to send the bytes, it appears to work (the return is 1).
When I try to read the bytes, it also appears to work (the return is
1).

But it always gives me the return 1 when I read the bytes, even when
nothing is sent. So I don't know if my process is working. Can anyone
help me?

I use the code below to open the COM port:
HANDLE PortOpen(LPTSTR lptszPortName, DWORD* dwError)
{
DCB PortDCB;
COMMTIMEOUTS CommTimeouts;
HANDLE hPort;


// Open the serial port.
hPort = CreateFile(
lptszPortName, // Pointer to
the name of the port
GENERIC_READ | GENERIC_WRITE, // Access(read-write)
mode
0, // Share mode
NULL, // Pointer to the
security attribute
OPEN_EXISTING, // How to open the
serial port
0, // Port attributes
NULL // Handle to port
with attribute to copy
);

// If it fails to open the port, return FALSE.
if (INVALID_HANDLE_VALUE == hPort)
{
return INVALID_HANDLE_VALUE;
}

return hPort;
}

And the code below is to write data on the open port:
BOOL PortWrite(HANDLE hPort, BYTE* Bytes, DWORD dwBytesToWrite)
{
BYTE* ucptr;
BYTE* cptr;
DWORD dwBytesWritten;
DWORD dwBytesPacket;
DWORD dwBytesRemain;
int nCounter;
BOOL bRet;


bRet = FALSE;

ucptr = Bytes;
cptr = ucptr;

dwBytesRemain = dwBytesToWrite;
do
{
dwBytesPacket = (dwBytesRemain < PACKET_SIZE) ? dwBytesRemain :
PACKET_SIZE;

nCounter = 1;
do
{
bRet = WriteFile(hPort, ucptr, dwBytesPacket, &dwBytesWritten,
0);
nCounter++;
Sleep(300);
}
while ((bRet == FALSE) && (nCounter < 5));

if (bRet == FALSE)
return FALSE;

dwBytesRemain -= dwBytesWritten;
ucptr += dwBytesWritten;
}
while (dwBytesRemain > 0);

return TRUE;
}

The code below I use to read te data:
CString PortRead(HANDLE comPort, DWORD dwBytesToRead)
{
BOOL bResult;
BYTE * totalBytes; //total de bytes
BYTE * readBytes; //bytes parcialmente lidos
DWORD dwBytesRemain; //bytes restantes a serem lidos
DWORD dwBytesRead; //bytes lidos
DWORD dwBytesPacket; //tamanho do pacote

int nCounter;

dwBytesPacket = PACKET_SIZE;
dwBytesRemain = dwBytesToRead;
readBytes = 0;
bResult = ReadFile(comPort, &readBytes, dwBytesToRead, &dwBytesRead,
NULL);

CString s = (LPCTSTR)readBytes;

if (s == "")
return FALSE;

return s;

if (bResult == FALSE)
return FALSE;
}

Thanks,
Arthur

From: Ben Voigt [C++ MVP] on 29 Apr 2008 18:36

---

arthurclucas(a)gmail.com wrote:
> Hi everyone,
>
> I'm have two iPac Devices and I'm trying send some bytes from one to
> another via Bluetooth communication.
> I use the CreateFile command to send the data and the ReadFile command
> to read the data.
> In booth commands I use the appropriate COM port.
> When I try to send the bytes, it appears to work (the return is 1).
> When I try to read the bytes, it also appears to work (the return is
> 1).
>
> But it always gives me the return 1 when I read the bytes, even when
> nothing is sent. So I don't know if my process is working. Can anyone
> help me?
>

[snip]

> The code below I use to read te data:
> CString PortRead(HANDLE comPort, DWORD dwBytesToRead)
> {
> BOOL bResult;
> BYTE * totalBytes; //total de bytes
unused variable, delete

> BYTE * readBytes; //bytes parcialmente lidos
> DWORD dwBytesRemain; //bytes restantes a serem lidos
no logic for partial reads, this is also useless

> DWORD dwBytesRead; //bytes lidos
> DWORD dwBytesPacket; //tamanho do pacote
unused variable, delete

>
> int nCounter;
unused variable, delete

>
> dwBytesPacket = PACKET_SIZE;
> dwBytesRemain = dwBytesToRead;
> readBytes = 0;
Now your pointer is NULL.

> bResult = ReadFile(comPort, &readBytes, dwBytesToRead, &dwBytesRead,
> NULL);
You are reading into the pointer variable, not into a buffer. So you can
read at most (sizeof (BYTE*)) bytes, probably 4. Bad idea. You need to
allocate a buffer and pass a pointer to the buffer, not the address of a
pointer.

You need to check bResult here, before using the data.

>
> CString s = (LPCTSTR)readBytes;
Since the pointer got overwritten, it is garbage. This should cause your
program to crash.
Once you use a buffer properly, you have another problem because ReadFile
doesn't NUL-terminate the data.
Also you should never use TCHAR with sockets, the data must be either
Unicode or not (on WinCE it is always Unicode).

>
> if (s == "")
> return FALSE;
>
> return s;
>
> if (bResult == FALSE)
> return FALSE;
and this code down here never runs, because you already returned. End
result is you never even checked bResult.


> }
>
> Thanks,
> Arthur

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