C / C++ / MFC

6-Apr-08 19:53

Hello everyone,

I read the code for class CComMultiThreadModelNoCS of ATL. What means,

--------------------
(Section Threading Model Support, Chapter 3 Objects in ATL, ATL Internals)
CComMultiThreadModelNoCS is designed for multi-threaded objects the eschew object-level locking in favor of a more fine-grained scehme?
--------------------

My understanding is the object designed could use other approaches other than critical section, like mutex/event to do synchronization. Not sure whether my understanding is correct?

thanks in advance,
George

ATL bug of CComPtr?

George_George6-Apr-08 19:42

6-Apr-08 19:42

Hello everyone,

In the ATL Internals book, one form of constructor of CComQIPtr is implemented as this,

CComQIPtr (IUnknown* lp)
{
    p = NULL; if (lp != NULL) lp -> QueryInterface (*piid, (void**)&p);
}

I think there is a bug when QueryInterface fails, and the original value of member variable p is overwritten.

I found the in MSVC 2008, the implementation is,

atlcomcli.h

	CComQIPtr(_In_opt_ IUnknown* lp) throw()
	{
		if (lp != NULL)
			lp->QueryInterface(*piid, (void **)&p);
	}

Seems the bug is fixed? Is it a bug in old version of ATL or a bug in the book? Smile | :)

thanks in advance,
George

CPallini6-Apr-08 22:14

CPallini

6-Apr-08 22:14

George_George wrote:
I think there is a bug when QueryInterface fails

I see no bug.

George_George wrote:
and the original value of member variable p is overwritten.

The original variable? It's a constructor George!
When QueryInterface fails, having a null pointer, IMHO, is the expected behaviour.

George_George wrote:
Seems the bug is fixed? Is it a bug in old version of ATL or a bug in the book?

The essence of the behaviour doesn't change here.
Smile | :)

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

George_George6-Apr-08 22:26

6-Apr-08 22:26

Thanks CPallini,

CPallini wrote:
When QueryInterface fails, having a null pointer, IMHO, is the expected behaviour.

You mean when QueryInterface fails, QueryInterface will set the input parameter pointer to null?

regards,
George

CPallini6-Apr-08 23:09

CPallini

6-Apr-08 23:09

George_George wrote:
You mean when QueryInterface fails, QueryInterface will set the input parameter pointer to null?

Yes. You know that.
Smile | :)

George_George6-Apr-08 23:12

Problem with Binary Tree Program [modified]

6-Apr-08 23:12

Thanks CPallini,

Question answered. I previously wrongly think it is assignment operator, other than constructor. Smile | :)

regards,
George

Member 42588976-Apr-08 17:58

Member 4258897

6-Apr-08 17:58

In my program, I pick a pivot p from a database S of strings, compute the median r of the distances of other string objects to p and then divide the other objects into roughly equal-sized subsets S1 and S2 as follows:
<pre>
S1={o e S \{p}|d(p,o)<r}
S2={o e S \{p}|d(p,o)>=r}
</pre>
where d(p,o) is the distance of the database object o to pivot p.Thus, the objects in S1 are inside the ball of radius r around p, while the objects in S2 are outside this ball. Applying this rule recursively leads to a binary tree,where a pivot object is stored in each internal node, with the left and right subtrees corresponding to the subsets inside and outside the corresponding ball,respectively.

Below I give the function for the above criteria but when I call the function from main and try to print the tree in preorder, nothing gets printed nor does the program terminate. I will really appreciate if someone can help me find the errors in my code and where I am going wrong:

<pre>
void query_ball()
{

string str;
int i=0,p;
int arr[1000];
char B[40];
char C[40];
vector<string> myStrings(1000);
int r;
int n1;

ifstream file("text.txt"); //this file is the database containing 1000 strings

for(p=0;p<1000;p++)
{
getline(file,str);
strcpy(B,str.c_str());
myStrings[p]=B; // copying the file strings to vector myStrings
}
srand(time(0));
int pos;
pos=rand()%1000;
strcpy(C,myStrings[pos].c_str()); // C is the pivot picked randomly

for(i=pos;i<=998;i++) // deleting element at myStrings[pos] which contains pivot C
myStrings[i]=myStrings[i+1];

myStrings[i]="";

for(p=0;p<999;p++)
{
strcpy(B,myStrings[p].c_str());
arr[p]=edit(B,C); // arr contains edit distances between other string objects and pivot C
}

/*edit function relates to edit distances of pivot from other string objects. An edit distance between 2 strings is found by changing one string to another with the minimum number of insertions, deletions and/or replacement of characters in the strings.*/

n1=(999+1)/2;
r=arr[n1]; // r is the median of the distances of other objects to pivot C

for (p=-1; p<999; p++) //p starts with -1 to check first if Root is Null
{

if (Root == NULL)
{
Root = new TreeNode();
Root->val = C;
}

else
{
TreeNode* temp = Root;
while(temp!=NULL)
{ strcpy(B,myStrings[p].c_str());

if (edit(B,C)<r) // checking distances inside ball of radius r
{
if (temp->LChild==NULL)
{ TreeNode* t = new TreeNode();
t->val = B;

temp->LChild=t;
}
else
{
TreeNode* t = new TreeNode();
t->val = B;
temp->LChild = temp->LChild->t;

}
}

if (edit(B,C)>=r) // checking distances outside ball of radius r
{

if (temp->RChild==NULL)
{ TreeNode* t = new TreeNode();
t->val = B;

temp->RChild=t;
}

else
{
TreeNode* t = new TreeNode();
t->val = B;
temp->RChild = temp->RChild->t;

}
}
}

}
}

}

</pre>

<div class="ForumMod">modified on Monday, April 7, 2008 12:18 AM</div>

Re: Problem with Binary Tree Program

Member 42588978-Apr-08 16:32

Member 4258897

8-Apr-08 16:32

Referring to the above codes, I see that when I print the children of the left tree, it gives me segmentation fault. Can somebody please point out why I am getting segmentation fault for the cout statement in the codes below:

 if (edit(B,C)<r)>
        {
 
           if (temp->LCh==NULL)
            { 
              t1->val = B;

              temp->LCh=t1;
           
            }
       else
           {         

                     TreeNode* t = new TreeNode();
                     t->val = B;
                                  
                     temp->LCh=temp->LCh->t;         
                     cout<<temp->LCh->val<<endl; // gives segmentation fault
           }
        }

</r)>

Any help much appreciated.

how to spy++ a windows which will hide when it lose focus?

code_discuss6-Apr-08 17:24

code_discuss

6-Apr-08 17:24

I'd like to use spy++ to watch on a window, but that window will hide automatically when it lose focus, which means it will hide as soon as I lauch/switch to spy++.

So how can I do that?

Re: how to spy++ a windows which will hide when it lose focus?

CPallini6-Apr-08 21:35

CPallini

6-Apr-08 21:35

Actually Spy++ shows hidden windows too.
Smile | :)

Re: how to spy++ a windows which will hide when it lose focus?

code_discuss6-Apr-08 21:55

code_discuss

6-Apr-08 21:55

Yes I know.
But now it's difficult for me to find that window using spy++.
The windows appears to be hidden, but it may already be destroyed. If it's destroyed when losing focus, I can't find it using spy++.

But I really want to find that window and find its class name, window text, ect, which info I can use to find them by code.
So.. Please help me out.

CStdioFile problem

lisoft6-Apr-08 16:24

lisoft

6-Apr-08 16:24

Hi all: I've got problem with CStdioFile::Open and need your help, below is the code sample:

<br />
CString m_filename="some absolute file path\name";<br />
CStdioFile m_file;<br />
if (!m_file.Open(m_filename,CFile::modeCreate|CFile::modeWrite))<br />
{<br />
     AfxMesageBox (_T("Can not open the file"));<br />
}<br />

I'm sure the absolute file path/name is correct and have read/write permission to the file location.

When I run this code from Visual Studio by press CTRL+F5, this code is OK and the file is opened sucessfully. But when running the program out of the studio, I got problem that get into the AfxMesageBox showing the file can not be open.

Lisoft

nisha000006-Apr-08 18:11

nisha00000

6-Apr-08 18:11

CString m_filename="some absolute file path\name";
CStdioFile m_file;
if (!m_file.fOpen(m_filename,CFile::modeCreate|CFile::modeWrite))
{
AfxMesageBox (_T("Can not open the file"));
}

Try this..
Actually CstdioFile used for creating file in runtime so u ll modify above ..

lisoft6-Apr-08 18:47

lisoft

6-Apr-08 18:47

You mean replace m_file.Open() with m_file.fOpen()? What is fOpen?

Lisoft

nisha000006-Apr-08 19:40

nisha00000

6-Apr-08 19:40

its just try ..if it is that create run time u may be add fopen

krmed7-Apr-08 1:50

krmed

7-Apr-08 1:50

The way you show your m_filename is not an absolute path, but a relative path.

When you run from within VS (Ctrl_F5) the default working directory is the same folder as your .sln/.vcproj file. Let's say it's "MyProg", thefore you would attempt to open the file in VS, the path would be

MyProg\some absolute file path\name

However, if you run it from the Windows Explorer (double click on it) the default directory would be the location of the .exe. In this case, it might be

MyProg\debug\some absolute file path\name

The CStdioFile.Open will not create directories if the don't exist, and that would cause it to fail.

Perhaps if you show the actual contents of your m_filename it may be helpful.

Hope that helps.

Karl - WK5M
PP-ASEL-IA (N43CS)
PGP Key: 0xDB02E193
PGP Key Fingerprint: 8F06 5A2E 2735 892B 821C 871A 0411 94EA DB02 E193

lisoft7-Apr-08 15:18

lisoft

7-Apr-08 15:18

Thanks for your help, but I'm always looking into the m_filename and I'm sure that was absolute. Something newly found today that when I call m_file.Open() I got an warnning message:

Warning: could not get volume information 'd:\Documents and Settings\mmn7xxl\My Documents\My Project\Program\WareHouseReport\"d:\'

. Can you figure this out for me?

Lisoft

krmed8-Apr-08 0:47

krmed

8-Apr-08 0:47

That string can't really be a file name.

lisoft wrote:
d:\Documents and Settings\mmn7xxl\My Documents\My Project\Program\WareHouseReport\"d:\

Show the actual code where you build that string and maybe we can help.

Karl - WK5M
PP-ASEL-IA (N43CS)
PGP Key: 0xDB02E193
PGP Key Fingerprint: 8F06 5A2E 2735 892B 821C 871A 0411 94EA DB02 E193