C / C++ / MFC

Re: How can Get RECT value?

19-Dec-08 2:30

Could CListCtrl::GetSubItemRect[^] do the job you want to do?

CPallini19-Dec-08 2:37

CPallini

19-Dec-08 2:37

Why dont' you use GetItemRect and GetSubItemRect?
Smile | :)

Exception handling in C++

San19-Dec-08 1:03

San

19-Dec-08 1:03

Hi all,

What is wrong in this problem. Is this the right way to handle?

#include <iostream.h>
class MyErrorClass
{

char *reason;
int *i;

public:

MyErrorClass(char *r)
{
i = new int[6];
cout<<;"Constructor<<endl;
reason = r;
cout<<reason<<<endl;

}

char* giveReason()
{
return reason;
}
~MyErrorClass()
{
cout<<"destructor"<<endl;
delete[] i;
}

};
void main()
{

try
{
throw MyErrorClass("error");
}
catch (MyErrorClass &e)
{
cout<<"Exception caught --- <<e.giveReason()<<endl;
}
}

Thanks
San

Re: Exception handling in C++ [modified]

Jijo.Raj19-Dec-08 1:54

19-Dec-08 1:54

I hope you got a crash when you run this code snippet. I rewrote it like this. It allocates the MyErrorClass then throw it. On the top level function, you can delete it. Check the code snippet.

void main() { try { throw new MyErrorClass("error"); } catch (MyErrorClass* e) { cout<<"Exception caught --- "<<e->giveReason()<<endl; delete e; } }

[Added] As pointed out by Stuart, it will be better to catch the exception object by reference itself. But here the problem is your MyErrorClass is not well written to handle its allocation which can cause crashes(I had). Hope you've already went thought Stuart's explanations.

Regards,
Jijo.

_____________________________________________________

http://weseetips.com[^] Visual C++ tips and tricks. Updated daily.

modified on Friday, December 19, 2008 9:46 AM

Stuart Dootson19-Dec-08 2:24

19-Dec-08 2:24

Ummm - no. You definitely should not get a crash when you throw an exception object (as opposed to an exception pointer). The exception declaration does not define the lifetime of the exception - the runtime copies it (or something like that, anyway).

Try the following - you'll find it doesn't crash...

#include <stdexcept>
#include <iostream>

int main(int, char**)
{
   try
   {
      throw std::runtime_error("Test");
   }
   catch(std::exception& e)
   {
      std::cerr << "Caught exception - " << e.what() << std::endl;
   };
}

Jijo.Raj19-Dec-08 2:29

19-Dec-08 2:29

Well Stuart, try with this code snippet. Its the same code snippet provided by Ron. I made it compilable. I'll be surprised if it didn't crashed in your system.

class MyErrorClass
{

char *reason;
int *i;

public:
   
   MyErrorClass(char *r)
   {
      i = new int[6];
      cout<<"Constructor"<<endl;
         reason = r;
      cout<<reason<<endl;
      
   }
   
   char* giveReason()
   {
      return reason;
   }
   ~MyErrorClass()
   {
      cout<<"destructor"<<endl;
      delete[] i;
   }
   
};
void main()
{
   
   try
   {
      throw MyErrorClass("error");
   }
   catch (MyErrorClass* e)
   {
      cout<<"Exception caught --- "<<e->giveReason()<<endl;
   }
}

Regards,
Jijo.

_____________________________________________________

http://weseetips.com[^] Visual C++ tips and tricks. Updated daily.

Stuart Dootson19-Dec-08 2:34

19-Dec-08 2:34

Yes, this code will crash - because you're throwing an object of type MyErrorClass and trying to catch a pointer to an object of type MyErrorClass.

With the original code, which has this line, catching an object (well, reference to an object) of type MyErrorClass

catch (MyErrorClass &e)

the code compiles, links and runs as expected.

Did you try it? I did.

Jijo.Raj19-Dec-08 2:41

19-Dec-08 2:41

Ah! Sorry, i did send you the wrong code. I forgot to rollback the changes made to the old code. I really meant - catch (MyErrorClass &e) will also crash. I'm posting the code snippet once again. Well, I'm using Visual Studio 6.0. Which one you're using? Well, the reason for crash is due to the fact that MyErrorClass::i is being de-allocated twice, since the copy constructor is not written for deep copy.

class MyErrorClass
{

char *reason;
int *i;

public:
   
   MyErrorClass(char *r)
   {
      i = new int[6];
      cout<<"Constructor"<<endl;
         reason = r;
      cout<<reason<<endl;
      
   }
   
   char* giveReason()
   {
      return reason;
   }
   ~MyErrorClass()
   {
      cout<<"destructor"<<endl;
      delete[] i;
   }
   
};
void main()
{
   
   try
   {
      throw MyErrorClass("error");
   }
   catch (MyErrorClass& e)
   {
      cout<<"Exception caught --- "<<e.giveReason()<<endl;
   }
}

Regards,
Jijo.

_____________________________________________________

http://weseetips.com[^] Visual C++ tips and tricks. Updated daily.

Stuart Dootson19-Dec-08 2:54

19-Dec-08 2:54

Jijo raj wrote:
Well, the reason for crash is due to the fact that MyErrorClass::i is being de-allocated twice, since the copy constructor is not written for deep copy

You're quite correct - I didn't get a crash because I compiled with a non-debug runtime library. Even so, I'd still recommend throwing objects, not pointers - the real solution is for the OP to write a better exception class, I think.

Jijo raj wrote:
I'm using Visual Studio 6.0. Which one you're using?

2003, 2005 and 2008 - certainly not VC6!!! The reason I don't use VC6 is because it is so primitive in terms of C++ language support.

Jijo.Raj19-Dec-08 3:25

19-Dec-08 3:25

Stuart Dootson wrote:
Even so, I'd still recommend throwing objects, not pointers - the real solution is for the OP to write a better exception class, I think.

You're right. Indeed, i did forget about C++ morels when i saw the crash. Cry | :((

Stuart Dootson wrote:
2003, 2005 and 2008 - certainly not VC6!!! The reason I don't use VC6 is because it is so primitive in terms of C++ language support.

Yep. That's right. But still my favorite due to the excellent fast IDE. Well, i'm waiting for VC10 which is supposed to be the new 6. Smile | :)

Regards,
Jijo.

_____________________________________________________

http://weseetips.com[^] Visual C++ tips and tricks. Updated daily.

Stuart Dootson19-Dec-08 3:42

Re: Exception handling in C++ [modified]

19-Dec-08 3:42

Jijo raj wrote:
still my favorite due to the excellent fast IDE

VS2003 and VS2005 are fast when you give them a 2.4GHz Core 2 Duo and 4GB of RAM to play with Smile | :)

VS2008...I'm not so fond of, the debugger especially seems sluggish.

Jijo raj wrote:
Well, i'm waiting for VC10 which is supposed to be the new 6.

It's not (IMO) - I've used the CTP, and it's a really an evolution of VS2008 - it did seem a bit quicker, though. And the compiler has C++0x features, like lambdas and type inferencing, which are uber-cool Smile | :)

Stuart Dootson19-Dec-08 2:27

19-Dec-08 2:27

Looks fine to me, aside from some formatting errors that cause compile-time errors.

Ignore the comments telling you to throw pointers to exception objects - throw the exception objects directly.

You may also want to derive from std::exception or std::runtime_error, to leverage the standard C++ exception classes?

Here's a minimal example of throwing exceptions with standard C++ exception classes:

#include <stdexcept>
#include <iostream>

int main(int, char**)
{
   try
   {
      throw std::runtime_error("Test");
   }
   catch(std::exception& e)
   {
      std::cerr << "Caught exception - " << e.what() << std::endl;
   };
}

modified on Friday, December 19, 2008 8:35 AM

Stuart Dootson19-Dec-08 2:58

How to prevent ScrollBar hiding in a ScrollView

19-Dec-08 2:58

As Jijo says, you get a crash (if you're using the right runtime) because your exception object isn't written in such a way that it can be copied correctly.

I would suggest changing i to be a std::vector<int> and reason to be a std::string, because these can be copied successfully (unlike raw pointers to dynamically allocated memory). You also don't need to bother deleteing them.

pauvc19-Dec-08 0:50

pauvc

19-Dec-08 0:50

Hello everebody.
I have two ScrollViews placed in a separate SplitterWnds - FirstView and SecondView. I need to sync vertical scrolling between these two views - when I scroll FirstView vertically, I need SecondView to be scrolled vertically by the same amount. Vertical sizes of the views (SetScrollSizes) are the same. So, I override OnScroll function in FirstView and retransmitt all the data from one view to another. If both of views have horizontal scroll bar - everything works just fine (LINEUP/LINEDOWN, PAGEUP/PAGEDOWN, MOUSEWHEEL). But I have a problem when FirstView hides horizontal scroll bar - SecondView scrolls up/down more than first by height of the horizontal scroll bar, and this is right, because it has horizontal scroll bar. But I do not want it to do it "right" Smile | :)

The solution is to prevent horizontal scroll bar in FirstView from hiding, I think. But I do not know where and how to do it in a scroll view. Or, maybe the solution is ...
Thank you for answering ...

FSCTL_GET_VOLUME_BITMAP

john563218-Dec-08 23:59

john5632

18-Dec-08 23:59

Hi All,
Actually I am looking for the free continues of NTFS file system.
How could I do that?

Is this possible with FSCTL_GET_VOLUME_BITMAP with DeviceIoControl?
If yes please help me to achieve this.

Thanks in Advance...

Jijo.Raj19-Dec-08 0:24

19-Dec-08 0:24

MPTP wrote:
Actually I am looking for the free continues of NTFS file system.

Do you mean free clusters?

Regards,
Jijo.

_____________________________________________________

http://weseetips.com[^] Visual C++ tips and tricks. Updated daily.

john563219-Dec-08 0:41

john5632

19-Dec-08 0:41

yes free cluster

Jijo.Raj19-Dec-08 0:46

19-Dec-08 0:46

In that case, i think FSCTL_GET_VOLUME_BITMAP will suits your need. Check this code snippet[^] about how to call it.

Regards,
Jijo.

_____________________________________________________

http://weseetips.com[^] Visual C++ tips and tricks. Updated daily.