C / C++ / MFC

Overlapped serial comunication

30-Dec-13 0:44

See http://msdn.microsoft.com/en-us/library/ms235636(VS.90).aspx[^] for creating a DLL. If you want to use it from VB.NET, then see http://msdn.microsoft.com/en-us/library/aa288468(VS.71).aspx[^].

Veni, vidi, abiit domum

Palmitoxico29-Dec-13 11:55

Palmitoxico

29-Dec-13 11:55

Hi,

I'm have been trying to write an code in C++ by using the Win32 API to communicate through the RS232 serial port with equipment. It's a simplex communication (only the equipment sends data in blocks of 289 bytes). I'm using an dedicated thread to read the serial port. Firstly I tried to use non-overlapped communication, but I realized that is impossible to close the serial port if there's no data incoming (the thread gets stuck on WaitCommEvent function). So I tried to use overlapped I/O and WaitForMultipleObjects to solve this problem:

C++

void *SerialRead(void *param)  // param is a dummy pointer
{
	OVERLAPPED overlapped;
	
	memset( &overlapped, 0, sizeof(overlapped) );
	overlapped.hEvent = CreateEvent( NULL, TRUE, FALSE, NULL );

	SerialEvents[0] = overlapped.hEvent;
	
	ReadFile(SerialPort, SerialBuffer, 289, &dwBytesRead, &overlapped);//Try to read 289 bytes
	
    
	while (WaitForMultipleObjects(2, SerialEvents, false, INFINITE) == WAIT_OBJECT_0) //Wait for some event, if is an serial port event, executes de loop, if not, exit.
	{

		//...
		//Do stuff
		ReadFile(SerialPort, SerialBuffer, 289, &dwBytesRead, &overlapped); //Attempt to read the next 289 bytes
	}

	ClosePort();
	return 0;
}

I use the function SetEvent(SerialEvents[1]); to close serial port on the main thread.

To open the serial port:

C++

SerialPort = CreateFile(PortName,
GENERIC_READ|GENERIC_WRITE,//access ( read and write)
0,    //(share) 0:cannot share the COM port
0,    //security  (None)                
OPEN_EXISTING,// creation : open_existing
FILE_FLAG_OVERLAPPED,    // overlapped I/O
0// no templates file for COM port...
);

The problem is that even if I recive the 289 bytes, the thread keeps wating the function "WaitForMultipleObjects" return. If I recive the next 289 bytes the WaitForMultipleObjects function returns, but the data are mixed.

Someone could help me?

Richard MacCutchan29-Dec-13 22:52

29-Dec-13 22:52

You have created 1 event but your call to WaitForMultipleObjects[^] says that there are 2 events. You also make no attempt to check the return value from WaitForMultipleObjects so you do not really know what is happening.

Veni, vidi, abiit domum

Palmitoxico30-Dec-13 8:09

Palmitoxico

30-Dec-13 8:09

I forgot to mention that I created the other envent (SerialEvents[1]) on the main thread:

C++

SerialEvents[1] = CreateEvent(NULL, FALSE, FALSE, NULL);

This event is used to close the serial port (signaled by the main thread when user press the close button) and it is working!.

I used the GetLastError() function after WaitForMultipleObjects(), and it returns "ERROR_IO_PENDING". What could it be? I'm sure that the equipment is sending all 289 bytes!

Richard Andrew x6430-Dec-13 9:26

Richard Andrew x64

30-Dec-13 9:26

ERROR_IO_PENDING is a normal return value that indicates that the transfer is taking place in the background.

When you get that return value, you're supposed to wait on the event, then when the event is signaled, call GetOverlappedResult().

Look up that function, and you'll see how it works.

The difficult we do right away...
...the impossible takes slightly longer.

how to initialize array of variable length?

Palmitoxico31-Dec-13 2:32

Palmitoxico

31-Dec-13 2:32

Thanks for reply, I discovered the problem. It was that on setup when openning the serial port I was calling GetCommState() function before SetCommState(), so it was overwriting the DCB structure configuration, setting a wrong baud rate value. I fix it and now it's working wonderfully!

Le@rner27-Dec-13 21:18

27-Dec-13 21:18

hi all,

why not initialize the array of variable length why there is always need to assign size first.

how can I do this

int buffer_length;

buffer_length=lenth of some string.

BYTE byte_buffer[buffer_length];

can anyody help me for this.

thanks.

Randor 27-Dec-13 21:36

Randor

27-Dec-13 21:36

Hi,

Le@rner wrote:
can anyody help me for this.

Check out the std::vector class.[^]
You can also create it on the heap:

C++

PBYTE buf = new BYTE[buffer_length];

Best Wishes,
-David Delaune

Le@rner20-Jan-14 21:26

20-Jan-14 21:26

here if the buffer_length=190 its generate out of memory exception.

PBYTE buf = new BYTE[buffer_length];

it means it not working after certain limit.

thanks.

Richard MacCutchan27-Dec-13 22:34

27-Dec-13 22:34

See http://www.cprogramming.com/tutorial/c-tutorial.html[^].

Veni, vidi, abiit domum

Albert Holguin28-Dec-13 10:05

Albert Holguin

28-Dec-13 10:05

If you need a dynamic array (one that changes sizes), you need to allocate it dynamically on the heap.

In C++ you use new (along with corresponding delete after you're done with it).
In C you use malloc (along with corresponding free after you're done with it).

Failure to deallocate will result in memory leaks.

In addition to those options, you can use "containers", which are essentially classes that "contain" the dynamic array. A few of these options include std::vector, std::array, among others (most libraries including MFC have at least a couple of different container options).

David Crow3-Jan-14 4:28

David Crow

3-Jan-14 4:28

How about:

const int buffer_length = length of some string;
BYTE byte_buffer[buffer_length];

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Le@rner19-Jan-14 22:47

help me to generate MD5 of Binary hash value.

19-Jan-14 22:47

thanks everybody...

Le@rner26-Dec-13 21:33

26-Dec-13 21:33

hi all,

I want to generate the MD5 of given Unicode Binary hash value.

its done in c# like:

MD5 md5Hash = MD5.Create();

 byte[] md5Buf = System.Text.UnicodeEncoding.Unicode.GetBytes(binary_hash_value);
            byte[] md5Hash_buf = md5Hash.ComputeHash(md5Buf);

            // Convert the encrypted bytes back to a string (base 16)
            string hashString = "";

            for (int i = 0; i < md5Hash_buf.Length; i++)
            {
                hashString += Convert.ToString(md5Hash_buf[i], 16).PadLeft(2, '0');
            }


            hashString.PadLeft(32, '0');

            textBox3.Text = hashString;

but its done in my vc++ project can anybody help me to do this.

thanks in advance.

Richard MacCutchan26-Dec-13 22:25

26-Dec-13 22:25

In C/C++ you just treat the Unicode string as an array of bytes, no need for any conversion operations.

Veni, vidi, abiit domum

Le@rner26-Dec-13 23:45

26-Dec-13 23:45

I need md5 of given string only the Unicode string not fulfill my requirement according to this code md5 value of hello "fd186dd49a16b1bf2bd2f44e495e14c9"
Unicode value is "680065006c006c006f00"

and in vc++ Unicode value of it "00680065006C006C006F"

how can I get here the its md5 value please assist me...

Richard MacCutchan27-Dec-13 0:08

27-Dec-13 0:08

If your original string is in Unicode then the MD5 hash will not be the same as the ASCII representation. If it is a prerequisite for what you want to do then convert your text to ASCII before hashing. Take a look at Example C Program: Creating an MD5 Hash from File Content[^] for further help.

Veni, vidi, abiit domum

Le@rner27-Dec-13 2:03

27-Dec-13 2:03

I want to generate "fd186dd49a16b1bf2bd2f44e495e14c9" from hex value of hello = 680065006c006c006f00

but I the example its generate md5 ="5d41402abc4b2a76b9719d911017c592" from value hello

please help

Richard MacCutchan27-Dec-13 3:26

27-Dec-13 3:26

I already suggested that you can convert the Unicode characters to ASCII as a test sample. You may also like to spend some more time studying MD5 and how it is used.

Veni, vidi, abiit domum

Randor 27-Dec-13 10:51

Randor

27-Dec-13 10:51

Hi,

Hope you had a great Christmas holiday. Could not help but notice that '680065006c006c006f00' is an array of BYTE representing the unicode version of the string 'hello'. You can easily do this:

C++

//Various #includes...
#define LENGTH 16

int _tmain(int argc, _TCHAR* argv[])
{
	HCRYPTPROV p = 0;
	HCRYPTHASH h = 0;
	DWORD dwError=0;
	if(CryptAcquireContext(&p,NULL,NULL,PROV_RSA_FULL,CRYPT_VERIFYCONTEXT))
	{
			DWORD length = LENGTH;
			BYTE md5[LENGTH];
			BYTE buf[LENGTH];
			if(CryptCreateHash(p,CALG_MD5, 0, 0, &h))
			{
				wsprintfW((LPWSTR)buf,L"hello");
				if(CryptHashData(h, buf, wcslen((LPWSTR)buf) * sizeof(WCHAR), 0))
				{
					if(0 == dwError && CryptGetHashParam(h, HP_HASHVAL, md5, &length, 0))
					{
						std::cout << std::setfill('0');
						std::for_each(md5,md5+LENGTH,
										[](BYTE b)
										{
											std::cout << std::setw(2) << std::hex << static_cast<int>(b);
										});
						std::cout << std::endl;
					}
				}
			}
	}
	return 0;
}

Output: fd186dd49a16b1bf2bd2f44e495e14c9

Best Wishes,
-David Delaune

Le@rner27-Dec-13 17:30