Error while fetching null value - C / C++ / MFC Discussion Boards

Richard MacCutchan18-Jul-11 21:11

18-Jul-11 21:11

If this has been out of use for 2 years then I presume you only use it for personal projects. If that is the case then I would suggest you forget VC6 (unless you really need MFC) and go for the Visual Studio Express editions[^].

The best things in life are not things.

Re: fixing vc6 installation

John R. Shaw19-Jul-11 4:11

John R. Shaw

19-Jul-11 4:11

Good guess (MFC). I plan on the Resurrection of some old projects for the purpose of updating them. It helps to have the original development tools when working with old [GUI] code. Up until 2 years ago, all my cross-platform code included VC6 compatibility; I decided dropped that though.

Note: There are still commercial Apps the use MFC and posting for positions requiring it.

INTP
"Program testing can be used to show the presence of bugs, but never to show their absence." - Edsger Dijkstra
"I have never been lost, but I will admit to being confused for several weeks. " - Daniel Boone

Re: fixing vc6 installation

Richard MacCutchan19-Jul-11 6:09

Richard MacCutchan

19-Jul-11 6:09

John R. Shaw wrote:
There are still commercial Apps the use MFC and posting for positions requiring it.

I didn't mean to imply that MFC is no longer current, it's just that it is not available with the (free) Express editions of Visual C++.

The best things in life are not things.

Re: fixing vc6 installation

Rolf Kristensen27-Jul-11 12:22

Rolf Kristensen

27-Jul-11 12:22

There is a workaround for compiling old MFC applications in VS Express - How to compile MFC code in Visual C++ Express[^]

vcredist_x86.exe

RomTibi18-Jul-11 4:52

RomTibi

18-Jul-11 4:52

How can a program know if "Microsoft Visual C++ 2010 Redistributable Package (x86)" is installed. If possible, provide a sample code.

36. When you surround an army, leave an outlet free.
...
Do not press a desperate foe too hard.

SUN-TZU - Art of War

Re: vcredist_x86.exe

Rajesh R Subramanian18-Jul-11 5:40

Rajesh R Subramanian

18-Jul-11 5:40

From MSDN blogs: How to detect the presence of Visual C++ 2010 redistributable package[^].

There's also an alternative solution proposed on the page.

"Real men drive manual transmission" - Rajesh.

Re: vcredist_x86.exe

RomTibi18-Jul-11 5:47

RomTibi

18-Jul-11 5:47

Thank you!

36. When you surround an army, leave an outlet free.
...
Do not press a desperate foe too hard.

SUN-TZU - Art of War

Error while fetching null value

Pranit Kothari18-Jul-11 1:02

Pranit Kothari

18-Jul-11 1:02

Hello All,
I am using VC++/Com application and working with database.

I am using '_RecordsetPtr' to fetch database tables.

Here 'RsITEM' Macro to get particular column data. Everything works fine unless you encounter with NULL value. If values comes to be NULL, it just throw exception, and application crashes. Not allowing null values in database is not solution in my case.

Any help in this regard is highly appreciated.

Happy Programming.

Re: Error while fetching null value

dasblinkenlight18-Jul-11 2:44

dasblinkenlight

18-Jul-11 2:44

You need to check the Item for equality to VT_NULL before calling it's GetValue() method, like this[^].

problem in setting font to CComboBox in XP?

yogish29317-Jul-11 23:55

yogish293

17-Jul-11 23:55

Hi this is my code

LOGFONT lf;
memset(&lf, 0, sizeof(LOGFONT));
lf.lfHeight = 15;
lf.lfWeight = FW_REGULAR;
m_fontRegular.CreateFontIndirect(&lf);//m_fontRegular is object of CFont
m_ctrlComboBrowsers->SetFont(&m_fontRegular);// m_ctrlComboBrowsers is object of CComboBox

i am adding some string to combobox, problem is in XP machine combobox's dropdown list is not showing....
please help me.

Re: problem in setting font to CComboBox in XP?

«_Superman_»18-Jul-11 3:57

«_Superman_»

18-Jul-11 3:57

Have you done the layout of it in the dialog template properly?
In the dialog template, click on the drop down arrow of the combo box and resize the control by expanding it downwards.

«_Superman_»
I love work. It gives me something to do between weekends.

Microsoft MVP (Visual C++)

Polymorphism in C

Re: problem in setting font to CComboBox in XP?

yogish29318-Jul-11 20:41

yogish293

18-Jul-11 20:41

its created dynamically... problem was same what u told, size of the combobox was not expanded size, that was the issue.but my doubt is why this problem is coming only in xp?....

thanks..

How to delete char Array-Memory leak detection

Anu_Bala17-Jul-11 20:55

Anu_Bala

17-Jul-11 20:55

Hi,

Im declaring one char array in dialog Header File.

char *czTagGetVal;

And in one dialog class,im using that array as

void CGraphicsTagDlg:: GetTagLbl(int iLNo)
{
czTagGetVal = new char[50];			
memset(czTagGetVal,0,50);
.
.
.
}

After debugging i get the solution without any error.But when i close the applcaition,in Output window i saw lot of Memory leak detection.

So while closing the application i delete this array as

if(czTagGetVal)
	delete [] czTagGetVal;

But i get the error as

Windows has triggered a breakpoint in GraphicsTag.exe.
This may be due to a corruption of the heap, which indicates a bug in GraphicsTag.exe or any of the DLLs it has loaded.

How can i avoid this error.I used such kind of array in my applcation by using new operator.I want to delete all allocated memory.How can i do that.Pls help me.

Anu

Re: How to delete char Array-Memory leak detection

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]

Re: How to delete char Array-Memory leak detection

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

Code-o-mat

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<

Re: How to delete char Array-Memory leak detection

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

Re: How to delete char Array-Memory leak detection

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

Code-o-mat

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<

Re: How to delete char Array-Memory leak detection

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

Re: How to delete char Array-Memory leak detection

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

Code-o-mat

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<

Re: How to delete char Array-Memory leak detection

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.

Re: How to delete char Array-Memory leak detection

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.

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

Le@rner17-Jul-11 20:42

Le@rner

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.

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

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

Code-o-mat

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<

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

Le@rner17-Jul-11 20:56

Le@rner

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();
  }
}

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

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

Code-o-mat

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<

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