Re: Doubt in Serial communication - C / C++ / MFC Discussion Boards

Re: error in Access DB "Attempt to Update or Delete failed." and "Recordset is read-only"

Le@rner11-Jun-08 23:41

11-Jun-08 23:41

i m not using SQL Queries.

i m using CRecordset derived class, and directly assign the value of database variable to my dialog variable.

IN A DAY, WHEN YOU DON'T COME ACROSS ANY PROBLEMS - YOU CAN BE SURE THAT YOU ARE TRAVELLING IN A WRONG PATH

Re: error in Access DB "Attempt to Update or Delete failed." and "Recordset is read-only"

David Crow12-Jun-08 4:23

David Crow

12-Jun-08 4:23

ThatsMe. wrote:
how can i resolve them.

By opening the recordset as updateable.

"Love people and use things, not love things and use people." - Unknown

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Doubt in Serial communication

kuttiam11-Jun-08 19:47

kuttiam

11-Jun-08 19:47

Hi All,
I have a doubt in serial communication.
I am using non-overlapped io serial communication inside a thread in my application. So while coomunicating with the instrument, the thread gets blocked without blocking the application.
Now what is the difference between the above scenario and overlapped io communication?

Thanks for your reply Smile | :)

Re: Doubt in Serial communication

Cedric Moonen11-Jun-08 20:44

Cedric Moonen

11-Jun-08 20:44

In overlapped IO, the system will signal an event when the operation complete (read or write for example). But you still have to wait for that before processing your data (sure, you can't process your data if it is not available yet...). So, in general you still have to use a thread to wait on the event.
The big difference is that using this technique, you'll be able to wait for multiple events. With a blocking call, you can't do anything but wait until the function returns.

Cédric Moonen
Software developer

Charting control [v1.4]

Re: Doubt in Serial communication

kuttiam11-Jun-08 21:22

kuttiam

11-Jun-08 21:22

Hi Cedric,
Thanks for your reply.
If i place the blocking call in a thread, then the application will bot be blocked.
In this scenario what is the difference between the two types of communication?

Re: Doubt in Serial communication

Cedric Moonen11-Jun-08 21:42

Cedric Moonen

11-Jun-08 21:42

No, your application won't be blocked but you can't wait for other events in the same thread.
Another point I made: by using overlapped IO, you will in general wait for the event to be signaled (so the read operation to finish for example). To do that, you will block the thread which is calling WaitForSingleObject. So, in general, even when I use overlapped IO I handle that in a separate thread. The difference, as I said before, is that you can wait for multiple events to happen instead of just one. For example you could be reading two serial ports in the same thread.

Cédric Moonen
Software developer

Charting control [v1.4]

Re: Doubt in Serial communication

buntyrolln12-Jun-08 2:09

buntyrolln

12-Jun-08 2:09

Communications events can occur at any time in the course of using a communications port. The two steps involved in receiving notification of communications events are as follows:

* SetCommMask sets the desired events that cause a notification.
* WaitCommEvent issues a status check. The status check can be an overlapped or nonoverlapped operation, just as the read and write operations can be.

There are two interesting side effects of SetCommMask and WaitCommEvent. First, if the communications port is open for nonoverlapped operation, WaitCommEvent will be blocked until an event occurs. If another thread calls SetCommMask to set a new event mask, that thread will be blocked on the call to SetCommMask. The reason is that the original call to WaitCommEvent in the first thread is still executing. The call to SetCommMask blocks the thread until the WaitCommEvent function returns in the first thread. This side effect is universal for ports open for nonoverlapped I/O. If a thread is blocked on any communications function and another thread calls a communications function, the second thread is blocked until the communications function returns in the first thread. The second interesting note about these functions is their use on a port open for overlapped operation. If SetCommMask sets a new event mask, any pending WaitCommEvent will complete successfully, and the event mask produced by the operation is NULL.

For more details you can refer link given below:
http://msdn.microsoft.com/en-us/library/ms810467.aspx[^]

buntyrolln

Re: Doubt in Serial communication

buntyrolln12-Jun-08 2:17

buntyrolln

12-Jun-08 2:17

Continuation of above reply ....
you can use overlapped-IO operation for communication with serial com port.

Read code snippet for overlapped-IO is given below:

DWORD dwRead;
BOOL fWaitingOnRead = FALSE;
OVERLAPPED osReader = {0};

// Create the overlapped event. Must be closed before exiting
// to avoid a handle leak.
osReader.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);

if (osReader.hEvent == NULL)
   // Error creating overlapped event; abort.

if (!fWaitingOnRead) {
   // Issue read operation.
   if (!ReadFile(hComm, lpBuf, READ_BUF_SIZE, &dwRead, &osReader)) {
      if (GetLastError() != ERROR_IO_PENDING)     // read not delayed?
         // Error in communications; report it.
      else
         fWaitingOnRead = TRUE;
   }
   else {    
      // read completed immediately
      HandleASuccessfulRead(lpBuf, dwRead);
    }
}

buntyrolln

How can get Index of Current Save Record in Access Database?

Le@rner11-Jun-08 19:21

Le@rner

11-Jun-08 19:21

Hi all,

I m working on VC++ 2005, MFC-SDI type application, I m using ODBC for connection of Access Database.

CRecordset use as Derived class of Database.

Here i want to get the index of Currently save Record.

Please tell me how can i do this.

I m waiting for your valuable suggestions.

Thanks in advance.

IN A DAY, WHEN YOU DON'T COME ACROSS ANY PROBLEMS - YOU CAN BE SURE THAT YOU ARE TRAVELLING IN A WRONG PATH

Re: How can get Index of Current Save Record in Access Database?

David Crow12-Jun-08 4:25

David Crow

12-Jun-08 4:25

ThatsMe. wrote:
CRecordset use as Derived class of Database.

CRecordset is derived from CObject not Database. If you have something different, perhaps that is the cause of your problem.

"Love people and use things, not love things and use people." - Unknown

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

CP IGNORE

leckey12-Jun-08 17:44

leckey

12-Jun-08 17:44

Cross poster.

Holidays! (June 13th)
http://craptasticnation.blogspot.com/[^]

Use of Keyboard on ListCtrl.

Le@rner11-Jun-08 19:14

Le@rner

11-Jun-08 19:14

Hi all,

In VC++ 2005, How can use keyboard on ListCtrl.

Because when i use Tab Key then the control not goes to ListCtrl.

please help me for this.

Thanks in advance.

IN A DAY, WHEN YOU DON'T COME ACROSS ANY PROBLEMS - YOU CAN BE SURE THAT YOU ARE TRAVELLING IN A WRONG PATH

Re: Use of Keyboard on ListCtrl.

Naveen11-Jun-08 19:42

Naveen

11-Jun-08 19:42

Did u specify the Tab stop style( WS_TABSTOP ) to list control?

nave

[OpenedFileFinder]

Re: Use of Keyboard on ListCtrl.

Le@rner11-Jun-08 20:03

Le@rner

11-Jun-08 20:03

Yes sir.

IN A DAY, WHEN YOU DON'T COME ACROSS ANY PROBLEMS - YOU CAN BE SURE THAT YOU ARE TRAVELLING IN A WRONG PATH

Re: Use of Keyboard on ListCtrl.

Naveen11-Jun-08 20:15

Naveen

11-Jun-08 20:15

Well even if the list control, got keyboard focus, there will not be any difference in the apperance unless one item is selected. so select one item and try pressing tab.

nave

[OpenedFileFinder]

modified on Thursday, June 12, 2008 2:22 AM

Re: Use of Keyboard on ListCtrl.

Le@rner11-Jun-08 20:38

Le@rner

11-Jun-08 20:38

Thanks.

IN A DAY, WHEN YOU DON'T COME ACROSS ANY PROBLEMS - YOU CAN BE SURE THAT YOU ARE TRAVELLING IN A WRONG PATH

How can get roundoff value?

Le@rner11-Jun-08 18:23

Le@rner

11-Jun-08 18:23

Hi all,

In my application after calculation i m get value in this form "2606.451613".

i want the after "." two digit value like "2606.45".

how can i do this.

Help me for this.

Thanks in advance.

IN A DAY, WHEN YOU DON'T COME ACROSS ANY PROBLEMS - YOU CAN BE SURE THAT YOU ARE TRAVELLING IN A WRONG PATH

Re: How can get roundoff value?

_AnsHUMAN_ 11-Jun-08 18:45

_AnsHUMAN_

11-Jun-08 18:45

CString::Format helps.

CString str;
str.Format("%.02f",f); // where f contains the value you want to truncate if it's a float value.

Somethings seem HARD to do, until we know how to do them.
Wink | ;-)

_AnShUmAn_

Re: How can get roundoff value?

Le@rner11-Jun-08 18:53

Le@rner

11-Jun-08 18:53

thanks.

IN A DAY, WHEN YOU DON'T COME ACROSS ANY PROBLEMS - YOU CAN BE SURE THAT YOU ARE TRAVELLING IN A WRONG PATH

Re: How can get roundoff value? [modified]

Rajesh R Subramanian11-Jun-08 19:03

Rajesh R Subramanian

11-Jun-08 19:03

The other answer you got was correct, but you don't need a CString object to do this. The format specification[^] (%.02f) is the one that does the trick.

Nobody can give you wiser advice than yourself. - Cicero
.·´¯`·->Rajesh<-·´¯`·.
Codeproject.com: Visual C++ MVP

Fixed link - June 12, 2008 3:47 AM

Re: How can get roundoff value?

Saurabh.Garg11-Jun-08 19:12

Saurabh.Garg

11-Jun-08 19:12

How does format specifiers for debugger solve the OP's problem?

-Saurabh

Re: How can get roundoff value?

Rajesh R Subramanian11-Jun-08 21:47

Rajesh R Subramanian

11-Jun-08 21:47

I got it now. I linked him to the format specifications recognized by the debugger. Link fixed, thanks for pointing out. And, my post was to emphasize that a CString object is not required to do something like that. Smile | :)

Nobody can give you wiser advice than yourself. - Cicero
.·´¯`·->Rajesh<-·´¯`·.
Codeproject.com: Visual C++ MVP

Re: How can get roundoff value?

Saurabh.Garg11-Jun-08 21:48

Saurabh.Garg

11-Jun-08 21:48

No problem. You are welcome.

-Saurabh

does declare variables must before functionary code in VS2005 using C language?

CooperWu11-Jun-08 17:29

CooperWu

11-Jun-08 17:29

example1, this is OK.

<br />
#include <stdio.h><br />
int main(void) {<br />
   int n = 5;<br />
   int m = 6;<br />
   printf("%d\n", n+m);<br />
}<br />
</stdio.h>

example2, error Frown | :(

<br />
#include <stdio.h><br />
int main(void) {<br />
   int n = 5;<br />
   int m = 6;<br />
   printf("%d\n", n+m);<br />
   int z = 9; // error here, error C2143: syntax error : missing ';' before 'type'<br />
}<br />
</stdio.h>

is there a compile options for allow declare variables after functionary code in VS2005 IDE ??

Rose | [Rose]

Glad to discuss with you and best wishes.

Re: does declare variables must before functionary code in VS2005 using C language?

Saurabh.Garg11-Jun-08 17:53

Saurabh.Garg

11-Jun-08 17:53

Yes VC++ do allow to put variables anywhere within function body. You are getting this error because you are compiling this code from a .c file. In C variables are allowed only at the begining of a function. Just change the file extension from c to cpp and it will compile.

-Saurabh

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