C / C++ / MFC

CPallini17-Jul-11 21:36

CPallini

17-Jul-11 21:36

You should change:

Anu_Bala wrote:
char *czTagGetVal;

C++

char *czTagGetVal = NULL;

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

Code-o-mat17-Jul-11 21:55

17-Jul-11 21:55

Without seeing more of your code i have 2 guesses: you are either writing into memory out of bounds (so e.g. you allocated space for 50 characters but are writing more than that into the buffer, 51 or 100 or... The other guess is, you are trying to free up memory you didn't allocate OR you are trying to free up the same block of memory twice.

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> //TODO: Implement signature here<

Anu_Bala17-Jul-11 22:14

Anu_Bala

17-Jul-11 22:14

Im getting value by using this code

glg_animation[iPage].viewport.GetResource("\\Tag\\String",&czTagGetVal);
sTagName = (CString)czTagGetVal;

In OnClose(),when i debug this part of code

if(czTagGetVal)
		delete [] czTagGetVal

czTagGetVal has value as "ALRMCAB ".So definitely it is less than 50 and also im allocating the memory using new and assign value also.But this error is coming.

I delete this char array at the end of the fucntion where it is actually using.But the same error is coming.

Anu

Code-o-mat17-Jul-11 22:31

17-Jul-11 22:31

Shouldn't this:

Anu_Bala wrote:
glg_animation[iPage].viewport.GetResource("\\Tag\\String",&czTagGetVal);

be this:

glg_animation[iPage].viewport.GetResource("\\Tag\\String",czTagGetVal);

?

But if you use this buffer in a function only, then why don't you simply declare it on the stack in the function?

void This_is_the_function()
{
  char czTagGetVal[50];
  ...
}

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> //TODO: Implement signature here<

Anu_Bala17-Jul-11 22:39

Anu_Bala

17-Jul-11 22:39

Actaully that GetResource() is third party fucntion(using DLL) and then GetResourceis decalred as

GetResource( char * res_name, char ** s_value );

So i have to use that.

Anu

Code-o-mat17-Jul-11 22:47

17-Jul-11 22:47

That suggests that the function will allocate the string for you, so you don't need to do it, probably just free it (of course that depends on that 3rd party library). So like this:

void this_is_the_function(...)
{
  char *czTagGetVal = NULL;
  
  glg_animation[iPage].viewport.GetResource("\\Tag\\String",&czTagGetVal);
  sTagName = (CString)czTagGetVal;  
  //Deallocate memory pointed by czTagGetVal????
  ...
}

Be careful with freeing up memory allocated by 3rd party things because if you don't do the de-allocation that is in pair with the allocation you can get unpredictable results.

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> //TODO: Implement signature here<

Stefan_Lang20-Jul-11 1:21

Stefan_Lang

20-Jul-11 1:21

Judging by that function signature, GetResource will either allocate a string for you, or return a pointer to a string it stores internally (or statically). In either case, the pointer you pass will be overwritten, and any memory previously allocated that this pointer used to point to will be lost!

So, what you should do is:

1. do not allocate memory yourself!
2. initialize the pointer with NULL instead, before calling GetResource()
3. Check the documentation of GetResource() whether or not it allocates memory that needs to be freed or not. If your delete causes an error, then most likely it shouldn't be deleted, or it already gets deleted by whoever manages these resources.

How to open and read/write from multiple serial ports at the same time?

Albert Holguin18-Jul-11 5:31

Albert Holguin

18-Jul-11 5:31

Possibilities for Error:
- You've already deallocated this memory block.
- If you allocated within a DLL, you should deallocate within the same DLL. Don't do memory management across DLL boundaries.

Memory Leak:
- If the function GetTagLbl() gets called more than once, you'll have leaking memory by only deleting once when closing.

Le@rner17-Jul-11 20:42

Re: How to open and read/write from multiple serial ports at the same time?

17-Jul-11 20:42

Hi all,

i am using CreateFile to open the port,its working fine when i am handle this with only single port.

but now i want to open multiple port at the same time and perform read/write operation on these ports.

In The open port method, it opens the first available port and when it gets the second it closes the opened one and then opens the next port and so on.

if (IsOpen())
  {
    //Close down the comms port
    BOOL bSuccess = CloseHandle(m_hComm);
    m_hComm = INVALID_HANDLE_VALUE;
    if (!bSuccess)
      TRACE(_T("Failed to close up the comms port, GetLastError:%d\n"), GetLastError());
  }
  
  //Free the event object we are using
  if (m_hEvent)
  {
    CloseHandle(m_hEvent);
    m_hEvent = NULL;
  }

//Call CreateFile to open up the comms port
  CString sPort;
  sPort.Format(_T("\\\\.\\COM%d"), nPort);
  m_hComm = CreateFile(sPort, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, NULL);

so please help me how can i do this.

thanks in advance.

Code-o-mat17-Jul-11 20:50

Re: How to open and read/write from multiple serial ports at the same time?

17-Jul-11 20:50

Are you possibly using the same instance of this class to open all your ports?

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> //TODO: Implement signature here<

Le@rner17-Jul-11 20:56

Re: How to open and read/write from multiple serial ports at the same time?

17-Jul-11 20:56

i am using it like this:

//CPort_Class handels all port operation like open/Close and read and write

//CAppClass its a main appclass

void CAppClass::fun1()
{
  for(int i=0; i<port_count;i++)
  {
    CPort_Class* p_c=new CPort_Class;
    p_c->Open()
   
    //some working

    p_c->Close();
  }
}

Code-o-mat17-Jul-11 21:36

Re: How to open and read/write from multiple serial ports at the same time?

17-Jul-11 21:36

This code opens a port and then later on closes it before going on with the next one. I thought you wanted to have multiple ports open at the same time. Could you clearify?

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> //TODO: Implement signature here<

Le@rner17-Jul-11 21:38

Re: How to open and read/write from multiple serial ports at the same time?

17-Jul-11 21:38

yes i want to open the multiple port at same time.

Code-o-mat17-Jul-11 21:52

Re: How to open and read/write from multiple serial ports at the same time?

17-Jul-11 21:52

The code fragment you have shown opens and closes the ports one-by-one. You should rethink your strategy i guess. Without knowing more about what exactly you are trying to achieve it is hard to guess on anything, but you could for example try strating a new thread for each port if there aren't too many ports you want to use (of course you would need to implement proper synchronization as needed), or you could have an array for the port class instances, something like this:

CPort_Class *ports = new CPort_Class[portcount]
for (int port = 0; port < portcount; port++) ports[port].Open();
...
//now you have an array of ports that are opened simulteniously, do what you need with them
...
for (int port = 0; port < portcount; port++) ports[port].Close(); //you could put a call to Close() in
                                                                  //the destructor of this class possibly
delete []ports;

This is a simplified code fragment, you would of course need to do error checks too.

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> //TODO: Implement signature here<

Le@rner17-Jul-11 22:05