C / C++ / MFC

25-Nov-04 4:05

How do you find the Middle node of a string , without calculating the length of the string?
How would you test it ?
What if the length was “n” ?
How many pointer variables are used?
Is this done recursively ?

Thanks

toxcct25-Nov-04 5:37

toxcct

25-Nov-04 5:37

for the example, i use a CString :

<font color=#0000FF>char</font> ExtractMiddleNode(<font color=#0000FF>const</font> CString& str) {
    <font color=#0000FF>return</font> str[(<font color=#0000FF>int</font>)(str.GetLength() / 2)];
}

i explain.
GetLength() gives the length of str.
GetLength()/2 so gives the middle of the string.
if the string contain 2n characters (where n is an integer), so, GetLength()/2 gives an integer, that is the position of the middle character.
if the string contains 2n+1 characters (with n still an integer), GetLength()/2 gives an integer+0.5. that's why a truncated the result with the (int) cast.

understand ? Smile | :)

TOXCCT >>> GEII power
[VisualCalc]

John R. Shaw25-Nov-04 6:37

25-Nov-04 6:37

When did they start calling a character a node?

GetLenghth() returns and interger and is divided by an interger. The result is an interger. Therefor, there is no need for the int cast.

int i = 11/2;
Result: i = 5;
double d = 11/2;
Result: d = 5.0

INTP
"The more help VB provides VB programmers, the more miserable your life as a C++ programmer becomes."
Andrew W. Troelsen

toxcct25-Nov-04 6:41

toxcct

25-Nov-04 6:41

John R. Shaw wrote:
When did they start calling a character a node?

don't know, i just used what dmxdmxdmx... said.

TOXCCT >>> GEII power
[VisualCalc]

dmxdmxdmx0525-Nov-04 7:28

25-Nov-04 7:28

I'm not allowed to do a GetLength ...!!!

Anyways, Can I use a binary search Tree?

John R. Shaw25-Nov-04 5:43

25-Nov-04 5:43

dmxdmxdmx05 wrote:
Middle node of a string

What does this mean?

Is it a C string "c-string"?
Is it a standard C++ string?
Is it a CString?

There are to many ways to manipulate strings inorder to answer this question with more information.

INTP
"The more help VB provides VB programmers, the more miserable your life as a C++ programmer becomes."
Andrew W. Troelsen

dmxdmxdmx0525-Nov-04 7:29

25-Nov-04 7:29

C string I guess.
like a char*

John R. Shaw25-Nov-04 7:44

25-Nov-04 7:44

Well if toxcct is correct and you want the middle character, then you will have to use strlen(), which counts the characters.

char* s = "any string of characters";
int len = strlen(s);
char mc = s[len/2];

This assumes single-byte character coding (like ASCII). Multi-byte character is a whole nother story.

Note: Both std::string and CString both store the length, so getting the length is faster then character counting.

INTP
"The more help VB provides VB programmers, the more miserable your life as a C++ programmer becomes."
Andrew W. Troelsen

dmxdmxdmx0525-Nov-04 9:18

25-Nov-04 9:18

I'm not allowed to get the length of the string.

I think this can be done using a Binary Search Tree. and using a recursive function.

Anyhow it was an interview question, in reality all your answers are acceptable otherwise.

John R. Shaw25-Nov-04 9:39

MFC Application Installation Problem

25-Nov-04 9:39

We sill want to know what a Middle Node is, strings do not have nodes. If I was asked that at an interview, that is what I would tell them.

The question does not realy make any since!

Now if the string was not a string but a series text objects (aka. nodes) strung together to represent a string (like a rich-text document), then yes a binary search would probably be best.

Note: All the text in a rich-text document (I believe internaly) is in one node. Until you change the color or font of part of the text, then is must be split up into more than one node. Each of those nodes can be accessed individualy (via code) and the attributs changed.

Oh well! If you know what a Middle Node in a string is please tell us!

INTP
"The more help VB provides VB programmers, the more miserable your life as a C++ programmer becomes."
Andrew W. Troelsen

Pradeep Samji25-Nov-04 3:50

Pradeep Samji

25-Nov-04 3:50

Hi! All

I dont know if this question is relevant to this forum but I have no other options. I have an MFC application for which I have created an installion using Install Shield. Iam installing the application on a Windows XP System. If I login under an administrator account, the software installs and runs properly. However when I login as any other user who does not have administrator privileges, the software refuses to run. I thought this might be a problem with registration of some of the related dll files and tried to register them manually but I get an error message saying "DllRegisterServer failed Error code 0x80040200". Some of these dlls have been created using ATL and some are the standard Microsoft dlls like Capicom.dll. Can anyone please help Cry | :((

. Thanks in advance.

Regards
Pradeep.

Re: MFC Application Installation Problem

Antony M Kancidrowski25-Nov-04 4:08

Antony M Kancidrowski

25-Nov-04 4:08

Unfortunately you have no choice. If the registration requires administative privileges then you must install with an account that has such privileges.

After installation you will be able to use the software under the other accounts that do not posess administrative privileges.

Ant.

I'm hard, yet soft.
I'm coloured, yet clear.
I'm fruity and sweet.
I'm jelly, what am I? Muse on it further, I shall return! - David Walliams (Little Britain)

Re: MFC Application Installation Problem

david_gilmour25-Nov-04 17:18

david_gilmour

25-Nov-04 17:18

Hi!

Thanks for the reply. I tried to login as a non-administrator and debug the application source code to see where it is crashing. The application object gets created but the control never reaches InitInstance. It crashes midway showing error in Kernel32.dll

Any ideas?

Thanks
Pradeep.

Help needed in MFC

Ibana25-Nov-04 3:01

Ibana

25-Nov-04 3:01

Hello,

I have a problem where I want to update two varibales in my View class through a dialog class CModalmodeDlg. When I press the "OK" button in the dialog I want two separate const char * members to be updated.

The first case is when I select a Cstring from a dropdown and sends it to a const char * member (m_Vectorname) in the view class. That works great,but It doesnt work for the secondview member (m_Modefreq). When a try to display m_Modefreq in the view class it gets all corrupted. But it gets it right when I display it in a messagebox through the dialog.

example.

m_Modefreq in messagebox= "45.23 Hz"

m_Modefreq in ViewClass = "^''*´"

Another observation is that when I in the dialogs OnBnClickedOk() set the second variable (m_Modefreq) to always be the same static value it displays it correct in the view.

below is a code snibbet,

[code]

void CModalmodeDlg::OnBnClickedOk()
{

//get the active view
CFrameWnd* wnd = (CFrameWnd*) AfxGetMainWnd();
if(wnd) m_pView = (CVtkSDIView*) wnd->GetActiveView();

//get the selected string from the dropdown.
CString str;
m_DropDown.GetLBText( idx,str);

const TCHAR *ptr;
ptr = str;

//update the first view member const char *m_Vectorname
//works fine
m_pView->m_Vectorname=(LPCTSTR)str;

int idx = m_DropDown2.GetCurSel();
m_pView->m_Modeindex=idx;

//the method ReturnMode returns a string depending on which index is selected
//from the DropDown.

Currentstring =m_pView->ReturnMode(idx);

//Here I want the other const char * member (m_Modefreq) to be updated.
//it prints out the right in a messagebox but as soon as I try to display it in the view //class it gets all corrupted.

m_pView->m_Modefreq=Currentstring.c_str();

[/code]

When I set it to a static value

[code]

like this:
m_pView->m_Modefreq="45.2 Hz" it manage to update it right.

[/code]

I dont really know what to do about this, please letme know if you have any ideas!

Regards Peter

Niklas L25-Nov-04 3:13

Niklas L

25-Nov-04 3:13

m_pView->m_Modefreq=Currentstring.c_str();

This is the error. Currentstring is dialog local std::string. You are just doing a shallow copy of its internal pointer. When the dialog ends, the strings destructor destroys its contents.

You need a deep copy.

If you use a std::string or a CString in your view class, it will be ok. Otherwise you'll have to do the memory management yourself with new, strcpy and delete, which also works.

Joaquín M López Muñoz25-Nov-04 3:21

Joaquín M López Muñoz

25-Nov-04 3:21

The problem most likely lies here:

m_pView->m_Modefreq=Currentstring.c_str();

You are storing a pointer to the internal contents of Currentstring into m_pView->m_Modefreq, but this internal contents can change (or be deleted) as soon as Currentstring is modified or destroyed. In your snippet it is not clear whether Currentstring is a local variable or not: if the former, then the char buffer pointed to by m_Modefreq will be destroyed as soon as CModalmodeDlg::OnBnClickedOk exists.

As a general rule of thumb, never store the pointer returned by std::string::c_string. To solve your particular problem, change the type of m_Modefreq to a std::string.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo
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Ibana25-Nov-04 7:23

Ibana

25-Nov-04 7:23

Hi,

Thanks for your quick replys, to bad that I didn't notice until now Smile | :)

I will try both of the tips that has been suggested. Niklas you suggested that I should do a deepcopy, I suppose you mean create a new, strcpy, and then pass it, then delete it.

I realized that the buffer that the m_Modefreq points to will be destroyed but how come the other passing of data works.If you remember from my first thread I converted an CString str and passed it to a const char * m_Vectorname. Shouldn't that pointer also be corrupted as the other one since it points to a buffer that is being destroyed when it exists the metohd?

//get the selected string from the dropdown.
CString str;
m_DropDown.GetLBText( idx,str);

const TCHAR *ptr;
ptr = str;

//update the first view member const char *m_Vectorname
//works fine
m_pView->m_Vectorname=(LPCTSTR)str;