Overloading operator [ ] - C / C++ / MFC Discussion Boards

Re: 'class' type redefinition error

David Crow24-Mar-04 7:56

David Crow

24-Mar-04 7:56

What does the line in question look like? Are you including a .h file more than once?

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

C++ Generic Autorun app ?

Marc Piulachs24-Mar-04 4:38

Marc Piulachs

24-Mar-04 4:38

Hi , I've been searching the internet and CodeProject but I haven't found any customizable autorun app , All we know autorun dialogs present in every Microsoft CD . I'm a C# programmer and I don't have good c++ skills I'm sure that lots of programers like my are looking for some solution does anyone has any code to share ?

Thanks,

Re: C++ Generic Autorun app ?

jhwurmbach24-Mar-04 5:34

jhwurmbach

24-Mar-04 5:34

There is basically a Autorun.inf file in the root directory of the CD containing the name of a program to run when the CD is inserted.
This can be prevented by holding down the 'shift' key when inserting the CD. Also, it does not work with operating systems other than Windows.
I thought I just say that, because recently some very smart guy (SunnComm Technologies) invented a CD copy protection scheme on autoloading a program that prevented access to the CD. They sued the one who found out: Link here Roll eyes | :rolleyes:

"We trained hard, but it seemed that every time we were beginning to form up into teams we would be reorganised. I was to learn later in life that we tend to meet any new situation by reorganising: and a wonderful method it can be for creating the illusion of progress, while producing confusion, inefficiency and demoralisation."

-- Caius Petronius, Roman Consul, 66 A.D.

How to use CryptExportkey blob

chakra_r24-Mar-04 3:32

chakra_r

24-Mar-04 3:32

Hi
I like to use Blob data(non-encrypted) before calling CryptExportkey. So i can customize in such a way i can implement my own algorithm. How to do that.

chak

_control87 and signal(SIGFPE....)

prcarp24-Mar-04 3:03

prcarp

24-Mar-04 3:03

I have a very large mathematical model that runs continuously. I am trapping for math errors via _control87(_EM_INEXACT, _MCW_EM) and signal(SIGFPE, MyFPHandler). This part works and my routine (MyFPHandler) is called whenever there is a divide by zero, invalid operation, etc.. What I would like to do is get the program location of the offending operation. Is there a way to do this? The code must know somehow because, if I wanted to, I could resume execution from that point. However, in my case, I do a an _fpreset, and then longjump to a safe area that does some simple error reporting and cleanup.

Thanks,
Paul

GetDIBits and 98 Problem

Ceri24-Mar-04 2:43

Ceri

24-Mar-04 2:43

Hi I have a problem where I cannot use GetDIBits on 98, works fine on XP. I read somewhere that in 98 the width and height have to be divisable by 4 so I even tried that with no avail.

Here is a snippet which works in XP but doesn't in 98. Has anybody got any clue why it's not working in 98

<br />
        <br />
        ...<br />
<br />
	HDC hBmDC = CreateCompatibleDC(NULL);<br />
	HBITMAP hB = CreateBitmap(16,16,1,24,pPixels);<br />
<br />
	bmiInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);<br />
<br />
	// get pixels from the original bitmap con verted to 24bits<br />
	int iRes = GetDIBits(hBmDC,hB,0,16,NULL,&bmiInfo,DIB_RGB_COLORS);<br />
<br />
        ...<br />
<br />

Thanks

Help - CPrintDialog as a child

Jason Carter24-Mar-04 2:41

Jason Carter

24-Mar-04 2:41

I am trying to use the CPrintDialog functionality, with my own template, as a child on a tabbed dialog in VC6. If I make the child dialog a CPrintDialog it does not initialise with the printer details. So I tried to make the Main dialog a CPrintDialog, still the child does not respond. I then put the Controls on the Main dialog, then MoveWindow them to the Child, this inits ok but no longer responds to any user interaction ( change of printer combo ). I have played a little with message routing and can now respond to combo change, but not Properties Button. Anyone any thoughts

Overloading operator [ ]

Imtiaz Murtaza24-Mar-04 0:58

Imtiaz Murtaza

24-Mar-04 0:58

What is the correct method to overload the operator []. I am doing something like:

class MyClass
    {
      
      const int operator[](const int i ) const;
  
      int& operator[](const int i );
      //...
    }

Now i want to invoke the operator [] as follows:

MyClass foo;

    int i = foo[j]; 
    foo[j] = i;

Strange that in both cases second operator of the above class always gets called. Can anyone tell me whats the problem and why not first operator gets called ??

Imtiaz

Re: Overloading operator [ ]

Mike Dimmick24-Mar-04 2:20

Mike Dimmick

24-Mar-04 2:20

IIRC, the rules of C++ say that if two functions differ only by const, the non-const version is preferred for a non-const object.

If foo was const, the first assignment would call const int MyClass::operator[](int) const while the second wouldn't compile (the error would probably say something like "'const int' is not an l-value").

C++ doesn't know the context of an array access, so you return a reference to the object to be assigned to if you want to allow assignment. If you want to be able to control assignment (e.g. inspect the value before assigning it), you typically need to return a proxy object from operator[]. The proxy object overloads operator= and is also convertible to the contained type (in this case, you'd probably supply operator int). You would place your 'setter' logic in operator=.

Stability. What an interesting concept. -- Chris Maunder

Re: Overloading operator [ ]

David Crow24-Mar-04 2:36

David Crow

24-Mar-04 2:36

From what I can tell, you only need one of the overridden methods. The second one can be used on either the left or the right side of an assignment statement. Consider this example:

class MyClass
{            
public:
    MyClass()
    {
        arr[0] = 2;
        arr[1] = 4;
        arr[2] = 6;
    }
 
    int& operator[](const int i )
    {
        return arr[i];
    }
 
    int arr[3];
};
 
MyClass foo;    
int j = 0,
    i = foo[j]; // assigns the value 2 to i
foo[2] = i;     // assigns the value 2 to the third item in the array

The reason has to do with the function returning a reference to arr. It's being treated as if you had written:

MyClass foo;    
int j = 0,
    i = foo.arr[j];
foo.arr[2] = i;

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

Re: Overloading operator [ ]

Ryan Binns24-Mar-04 3:44

Ryan Binns

24-Mar-04 3:44

DavidCrow wrote:
From what I can tell, you only need one of the overridden methods. The second one can be used on either the left or the right side of an assignment statement.

Unless you want to call it on a const object to read the value...

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

System performance comparison

Shree24-Mar-04 0:55

Shree

24-Mar-04 0:55

I need to watch for a particular window on the screen. There are two approaches - to use a timer, say with an interval 500 ms, and use the FindWindow() function to check if that window has appeared. Another would be to use a system wide hook to monitor all events, filter out the window create events, and check the caption. Which one would take less system resources.

Is there a way to compare system performance with background processes running?

MFC Views Documents, and Modal windows :_-)

_psh_24-Mar-04 0:41

_psh_

24-Mar-04 0:41

Hi all,

I have two views, one of which is associated with a document. this view can be used to open a modal window which performs an operation on some data, and then it is closed. This window creates an array which i need the other view to access; the other view also needs access to the document data!

i can't see how to do this !
can anybody help ?

Paul.

When does it occur the worst case in Quicksort algorithm ?

nguyen_nd24-Mar-04 0:34

nguyen_nd

24-Mar-04 0:34

Hi Everybody !
Could you tell me when it occurs the worst case (n*n) and the best case in quick sort algorithm ?

Thank,
Nguyen

nguyen_nd

Re: When does it occur the worst case in Quicksort algorithm ?

Maximilien24-Mar-04 0:54

Maximilien

24-Mar-04 0:54

I'd say let professor google answer this ...

anyway, if I remember correctly, it's when the data is already sorted; but I don't remember the justification ...

Maximilien Lincourt
Your Head A Splode - Strong Bad

Re: When does it occur the worst case in Quicksort algorithm ?

David Crow24-Mar-04 2:43

David Crow

24-Mar-04 2:43

The partition-exchange sort (i.e., quicksort) algorithm performs the worst when the data is already sorted. Its best case is O(N lg N).

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

EDK

viliam24-Mar-04 0:03

viliam

24-Mar-04 0:03

Does anyone know direct download link for
Microsoft Exchange Development Kit (EDK)
I am not able to find it on Microsoft pages.
Thanx

viliam

Re: EDK

Mike Dimmick24-Mar-04 2:23

Mike Dimmick

24-Mar-04 2:23

Google for "exchange sdk" gets you http://www.microsoft.com/downloads/details.aspx?FamilyId=0C1B91E9-5172-4BA3-89E4-AA23CD95FA8C&displaylang=en[^].

Stability. What an interesting concept. -- Chris Maunder

Re: EDK

viliam24-Mar-04 3:44

viliam

24-Mar-04 3:44

That is not exactly what I am looking for.
I need EDK (something like SDK)
Header, and Lib files and these are just
tools.
Thanx anyway

viliam

ATL Service Tutorial

Anonymous23-Mar-04 23:49

Anonymous

23-Mar-04 23:49

Hi all,

Where can i find atl service s tutorial for the very beginner?

10'x
Smile | :)

pocket pc Recent Programs

venkigdl23-Mar-04 23:29

venkigdl

23-Mar-04 23:29

Hi all,
I have an issue related to pocket pc.
I would like to find out how I can delete the most recently opened files or programs in the pocket pc..
I mean I have an uninstallation where I want to remove the icon in the most recently used program group.

thanking you

Re: pocket pc Recent Programs

Cedric Moonen23-Mar-04 23:33

Cedric Moonen

23-Mar-04 23:33

I don't have a solution but I think you'll have more replies if you try the Embedded/Mobile forum Big Grin | :-D

How to get most significant digit ?

Cedric Moonen23-Mar-04 22:55

Cedric Moonen

23-Mar-04 22:55

Hi !
I need to retrieve the most significant digit of a number. This must also be rounded to the inferior 'unit'.

Example:
I have 5238.12 and I must have 1000.00
I have 0.02578 and I must have 0.01000
I have 5.45 and I must have 1.00

Any idea ?
Thanks

Re: How to get most significant digit ?

Pedro Ruiz23-Mar-04 23:17

Pedro Ruiz

23-Mar-04 23:17

Try this code:

d=pow(10,(int)floor(log10(f)));

f=input, d=output.

Re: How to get most significant digit ?

Cedric Moonen23-Mar-04 23:26

Cedric Moonen

23-Mar-04 23:26

Great

!
I found the same solution as you at the same time Big Grin | :-D

(but your explanation is simpler that mine Poke tongue | ;-P

)
Thanks

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