C / C++ / MFC

You need a Garbage Collector!

26-Jun-07 3:37

How can I ensure that the memory allocated by new gets deleted even if if do not give a delete operator.

CPallini26-Jun-07 3:41

CPallini

26-Jun-07 3:41

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.

... or smart pointers

Cedric Moonen26-Jun-07 3:47

Cedric Moonen

26-Jun-07 3:47

They'll manage deletion of the memory for you. But use it only when you need them, not putting them everywhere just because you are lazy Poke tongue | ;-P

Cédric Moonen
Software developer

Charting control [v1.2]

Re: Delete operator

led mike26-Jun-07 5:23

led mike

26-Jun-07 5:23

tom groezer wrote:
even if if do not give a delete operator.

what does "give a delete operator" mean? "give" is not a standard term used in software development. Here is a tip, don't make up your own terms when posting messages as it will be difficult to understand what you are saying.

Here is what you can do with a delete operator:

* overload
* call

Which one are you speaking about?

Re: Delete operator

tom groezer26-Jun-07 16:52

26-Jun-07 16:52

u call delete as in delete p;

Re: Delete operator

led mike27-Jun-07 4:45

led mike

27-Jun-07 4:45

tom groezer wrote:
How can I ensure that the memory allocated by new gets deleted even if if do not call a delete operator.

Then Cedric has given you the correct lead to the smart pointer[^]. However there are different models of smart pointers. There is one in STL called "auto_ptr" and there are others in the Boost library[^] that have different use models.

I recommend that you feel confident in your understanding of the different models before attempting to use them. Misuse of smart pointers can be worse than leaking memory.

Private functions

tom groezer26-Jun-07 3:30

26-Jun-07 3:30

If a base class has private functions how does the derived class call it without use of friends. is there some idiom where u can acess the private function of base class. Also is there a difference between a function and a method.

Re: Private functions

Cedric Moonen26-Jun-07 3:38

Cedric Moonen

26-Jun-07 3:38

tom groezer wrote:
If a base class has private functions how does the derived class call it without use of friends.

That's why C++ has the 'protected' keyword: your inherited class will be able to access the function but other classes won't be able to call it.

tom groezer wrote:
Also is there a difference between a function and a method.

It is just a 'naming' convention: a function is considered to be a global function and a method is a member function of a class.

Cédric Moonen
Software developer

Charting control [v1.2]

Re: Private functions

Roger Stoltz26-Jun-07 3:57

Roger Stoltz

26-Jun-07 3:57

tom groezer wrote:
is there some idiom where u can acess the private function of base class.

No, because it would not serve the purpose of having them private instead of protected.

Declaring members as private in a base class is to guard both variables and functions from being accessed and misused. They are used internally and the developer that designed the base class declared them private to guard against misuse.

I consider private declared base class members a powerful tool in order to make sure the class is used in the way it is supposed to be used. I think if someone feels the need for accessing private members of the base class there's a 5% chance the designer of the base class has made an error, but 95% chance that someone is trying to use the class in a way it wasn't supposed to.

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

Inline functions

tom groezer26-Jun-07 3:18

26-Jun-07 3:18

Can inline functions be inherited? How?

Re: Inline functions

Rajkumar R26-Jun-07 3:27

Rajkumar R

26-Jun-07 3:27

I think you are talking about classes

Yes. inline functions can be inherited.

inline functions can be defined in two ways.
1) functions defined with class declarations are by default inline.

2) if you defined the function to be inline in cpp files then those functions cannot be accesed outside its visibility.

Best Regards
Raj

help to solve this bug

James_Programmer26-Jun-07 3:04

26-Jun-07 3:04

Hi all,

I have developed one small application in VC++ using Visual Studio
I am going to fix memory leakages occurred in my program in the following code

char *m_tmpChar;
m_tmpChar=new char[100];
m_tmpChar="0";

now when I am going to delete this object with delete [] m_tmpChar it is showing me error dialog saying that assertion failed _crtisvalidheappointer(pUserData)

anyone please help me to solve this problem????

Cedric Moonen26-Jun-07 3:15

Cedric Moonen

26-Jun-07 3:15

You can't copy a char arry using =. You need to use strcpy for that purpose.

What you are doing here is storing the address of a new string in m_tmpChar. This memory was not allocated with new so you get a crash when you try to delete it.

Cédric Moonen
Software developer

Charting control [v1.2]

Iain Clarke, Warrior Programmer

Iain Clarke, Warrior Programmer26-Jun-07 3:23

26-Jun-07 3:23

/* line 1 */ char *m_tmpChar;
/* line 2 */ m_tmpChar=new char[100];
/* line 3 */ m_tmpChar="0";
/* line 4 */ delete [] m_tmpChar;

That's because you're making a fundamental mistake. m_tmpChar is not some magic string type - its a pointer to a character.

In line 2, you allocate a patch of memory big enough for 100 chars, and make m_tmpChar point there.
In line 3, you make that variable point to another patch of memory that holds the character '0' followed by a NULL. This might even be read only, depending on complier settings. In the process, you've forgotten where your recently allocated lump of 100 bytes was.
In line 4, you are asking delete to free the "0" patch of memory, which certainly wasn't created by new. As you are in debug mode, you are getting errors.

So you have 2 bugs - (a) deleting memory which wasn't created with new [giving you the fault], and (b) not deleting memory that *was* created by new [giving you the leak].

That was the long explanation. The short explanation:

Ask your teacher about strcpy, or read your lecture notes.

Pointers are one of those bits of learning that is really strange and bizarre, until it all clicks in your head. Then its just dangerous if you're not careful.

Iain.

James_Programmer26-Jun-07 3:48

26-Jun-07 3:48

This is my complete code
char *m_tmpChar;
CString temp = m_list.GetItemText(0);
m_tmpChar="1";
RegSetValueEx(hCurKey,"",NULL,REG_SZ,(unsigned char*)m_tmpChar,strlen(m_tmpChar)+1);

Now in the above code it shows me Linkage error

So can you please give me solution with strcpy function

Thanks again!!!!!!

James_Programmer26-Jun-07 3:56

26-Jun-07 3:56

Sorry one line is missing

char *m_tmpChar;
m_tmpChar=new char[100];
CString temp = m_list.GetItemText(0);
m_tmpChar="1";
RegSetValueEx(hCurKey,"",NULL,REG_SZ,(unsigned char*)m_tmpChar,strlen(m_tmpChar)+1);

Iain Clarke, Warrior Programmer

Iain Clarke, Warrior Programmer26-Jun-07 4:33

26-Jun-07 4:33

For this code, you will get away with not using strcpy, but you will still have the buf when you come to delete m_tmpChar;

change m_tmpChar="1"; to strcpy (m_tmpChar, "1"); which will copy the fixed string 1null into your temporary buffer.

The RegSetValueEx call looks fine to me. If you are getting a linker error, then you need to see what function it it failing to link, find that, and see where it lives.

Iain.

James_Programmer26-Jun-07 5:00

26-Jun-07 5:00

Thank you so much sir!!!

Now I get solution for that error

Thanks again for your valuable time spent behind me

James_Programmer26-Jun-07 5:14

26-Jun-07 5:14

Hi, again I have a same problem for memory leakage

here I am using CFont class for setting my font but it gives me not perfect result at output

CFont* m_pBoldFont1;
m_pBoldFont1 = new CFont;
m_pBoldFont1->CreateFont(15,0,0,0,900,0,0,0,0,0,0,ANTIALIASED_QUALITY,0,"Arial");

CString test;
test.SetFont(m_pBoldFont1);
test.SetWindowText("test Section");

how can i free memory for the object(m_pBoldFont1) of CFont from memory
the above code gives me memory leakage error and also when I free memory
with delete operator it will display my string not correctly.

So, can you please help me to solve above problem

Thanks in advance!!!

Iain Clarke, Warrior Programmer

Iain Clarke, Warrior Programmer26-Jun-07 5:47

26-Jun-07 5:47

Um, CString doesn't have a SetFont method. Or a SetWindowText method. So your above code not only has a memory leak, it wouldn't compile. CString is just a handy holder for a bunch of characters all in a row.
I'm going to make a leap in the dark, and say you're confusing it with a Label in VB...

As for the other question...
You need to keep a copy of the font around.

class CMyDialog : public CDialog
{
public:
    CDialog (.....)
    {
        m_fMyFont.CreateSomehow ();
        .....
    }

    ....
    BOOL OnInitDialog ()
    {
        SetFont (&m_fMyFont);
        ....
        return CDialog::OnInitDialog ();
    }

    

protected:
    CFont m_fMyFont;
};

Obviously, I've removed a lot of boilerplate code. I'm assuming you have a dialog, or such. Create the font, and SetFont with a pointer to it. In the above example, the window will be destroyed, then the destructor of CMyDialog. At the end of that, the destructor for CFont will be called, tidying up the font.

Not all solutions involve pointers!

Iain.

James_Programmer26-Jun-07 6:01

26-Jun-07 6:01

Hi,

Sorry it's not a CString but it is a CTransparentStatic this is which I have taken from Codeproject site.

So, it is like CTransparentStatic and all the methods are maintained in this file.

So, please give me solution if possible

Thanks!!!