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Hi.
I am studying more advanced C++ via Scott Meyer's Effective STL. I have not read any of his previous books including the C++ series. He does an exceptional job introducing invaluable advices on the use of STL. I am still reading it.
He makes references to a term that I am not familiar with. He mentions "reference counting" about vector and string containers. What is it?
Thanks,
Kuphryn
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That means that every time you assign or copy a string, the string object does not copy the character data, instead it increments a count that keeps track of how many objects are using its buffer. For example:
string s1 = "foo";
string s2 (s1);
string s3;
s3 = s2; After making those three strings, there is only one copy of "foo" in memory, and all 3 string objects point to it. The string class only copies the character data if you modify a string, such as:
s3 += "bar";
--Mike--
Just released - 1ClickPicGrabber - Grab & organize pictures from your favorite web pages, with 1 click!
My really out-of-date homepage
Sonork-100.19012 Acid_Helm
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I have a quickie question for you:
On modern machines, especially with the memory typically available, how big a difference does it make to have a string class reference counted? Is it truly worth all the effort that goes into making the refcounting work correctly in all situations?
Just curious
¡El diablo está en mis pantalones! ¡Mire, mire!
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Yes depending on the circumstances. I can think of two scenarios where a string class with these features helps out.
Picture very large strings that are copied and moved around. I think there would be a very good increase in space and time savings.
Also think of a case where you will have a string that gets repeated 1000's of times. For instance an XML file that contains a set of records for peoples names, and the "name" tag is repeated over and over. Or even a home grown version of a large array of structs where the default entry is "default". New memory would only get allocated for the default string when the user changed the value.
Build a man a fire, and he will be warm for a day
Light a man on fire, and he will be warm for the rest of his life!
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Jim Crafton wrote:
On modern machines, especially with the memory typically available, how big a difference does it make to have a string class reference counted? Is it truly worth all the effort that goes into making the refcounting work correctly in all situations?
Oh, and it's not all about memory performance: Speed performance can be much improved with reference counting or COW (copy on write). It's much faster incrementing a counter than moving large blocks of memory; and still, in modern machines you can imagine building a typical dynamic HTML page at a server and you'll start seeing strings with 20k, 50k, 100k being moved around back and forward. This makes a great difference.
My latest articles:
XOR tricks for RAID data protection
Win32 process suspend/resume tool
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reference counting is where you keep track of how many variables hold a reference to a particular pointer.
Each time you set a variable to point to a pointer that is reference counted, you increment the reference count. Each time that variable is done with your object, and no longer uses that pointer, you decrement the reference count.
When the reference count reaches 0, it is safe to delete that pointer because nobody else is referencing that object.
Reference counting has become a very popular technique in safely managing dynamic memory when more than one object needs to hold a reference to a pointer.
COM uses reference counting extensively to manage its interface pointers.
Build a man a fire, and he will be warm for a day
Light a man on fire, and he will be warm for the rest of his life!
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Okay. Thanks everyone.
Kuphryn
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I wanted to display 10 bitmaps using CImageList
but why all the bitmaps were black
1.first ,I created a project "Cards",Imported 1,2,...,10
2.and I added variable in CCardsView
CImageList* m_pImageList
and the function
BOOL CCardsView::AddBitmap(UINT nResourceID)
{
CBitmap m_bmp;
if(m_bmp.LoadBitmap(nResourceID))
{
m_pImageList->Add(&m_bmp,RGB(256,256,256));
m_bmp.DeleteObject();
return TRUE;
}
return FALSE;
}
3.CCardsView::CCardsView()
{
// TODO: add construction code here
m_pImageList=new CImageList;
m_pImageList->Create(71,96,ILC_COLORDDB,256,1);
for(int i=1;i<11;i++)
{
AddBitmap(i);
}
}
4.CCardsView::~CCardsView()
{
if(m_pImageList!=NULL)
{
delete m_pImageList;
}
}
5.void CCardsView::OnDraw(CDC* pDC)
{
CCardsDoc* pDoc = GetDocument();
ASSERT_VALID(pDoc);
// TODO: add draw code for native data here
CPoint pos(0,0);
// m_pImageList->SetBkColor(CLR_NONE);
// m_pImageList->SetOverlayImage(0,1);
for(int i=0;i<10;i++)
{
m_pImageList->Draw(pDC,i,pos,ILD_NORMAL);
pos.x+=50;
}
}
Why?
--oly--
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<quote>
m_pImageList->Add(&m_bmp,RGB(256,256,256));
This might be a problem. Try to change it to RGB(0,0,0),
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I have tryed
but it did not work
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<br />
BOOL CCardsView::AddBitmap(UINT nResourceID)<br />
the above method take in ResourceID!! but you said
for(int i =1; i<11; i++)
AddBitmap(i)
check whether i is the appropriate resource name!!!!
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yeah
I added 10 bitmaps with id 1 to 10
what is the matter?
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if u want i can have look at your code!!! Send it to my email.!!
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but I have wrote it down in my question
pls help me
It has puzzled me for 3 days
and no one could give me a correct answer
--oly--
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You must pass the resource ID to AddBitmap, not the index of the bitmap. The resource ID will be found in resource.h.
Gary R. Wheeler
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Hi
I'd like to get the user's input from the console, if the user put in some text, this information will be put in a buffer, if the user type in nothing in and press enter then the program is terminated. But how do i know if the user has type in something???
i've attempted to play around with this, first with cin.getline, cin.get ...and finally come up with gets(), however it still seem has not done the job.
this is the code that i've attempted
<br />
char input[MAX_PATH];<br />
char *pInput = input;<br />
<br />
cout << "Enter the text " << endl;
<br />
char delimeter =(char)gets(input);
<br />
while( delimeter != '\r' )<br />
{<br />
<br />
<br />
cout << "Enter the text " << endl;<br />
delimeter =(char)gets(input);<br />
}<br />
<br />
Any ideas, helps or suggestions are highly appreciated!!!
Regard,
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getchar maybe what you need instead of gets.
Roger Stewart
"I Owe, I Owe, it's off to work I go..."
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Try something like this:
char input[MAX_PATH];
do {
cout << "Enter the text " << endl;
gets(input);
if (strlen(input) != 0) {
}
} while (strlen(input) != 0);
Gary R. Wheeler
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You may have problems mixing cin/cout and gets/printf. For console hacks, I use gets/printf.
/ravi
Let's put "civil" back in "civilization"
http://www.ravib.com
ravib@ravib.com
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I created a Win32 Console Application with MFC support. Everything was working fine until I decided to add ADOX. I have the code for access database interaction in a separate static library from the console application itself. I can build the library fine, but when I try to link it in with the console app, I get several linker errors that look something like this:
\PATH_TO_VC98\comutil.h(562) : error C2668 : 'memcpy' : ambiguous call to overloaded function
From what I understand, when you get this kind of error, it is from a naming collision of some sort. The only problem is that I haven't written my own 'memcpy'. I can only assume that the compiler sees two different versions on the system somewhere. The really strange part about the whole things is that the application builds fine when I am using the exact same code on a button handler in a GUI. I do have the Platform SDK installed (not sure if that matters). Anyone heard of this kind of thing? Please help!!!
-Matt
------------------------------------------
The 3 great virtues of a programmer:
Laziness, Impatience, and Hubris.
--Larry Wall
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In a listbox I want to handle the on LButtonDown so that I can quickly select items in a listbox. The default is the curent selection is only updated on LButtonUp. Any ideas?
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I'm so use to a lot of quirks coming from ClassWizard, I'm beginning to wonder whether it's normal.
For example, I instructed ClassWizard to add a new class for me, chose "New" and continued to fill in the class name and its derived class name (etc.). Then I click OK and CW produced a message saying it couldn't open the file I had just asked it to add. I clicked OK again and it came back with a message about how it found remants of the class I had just asked it to add (that it earlier said it couldn't).
I checked the workspace, checked Explorer and even brought the newly created file into the Source Editor and made modifications to it (etc.), compiled and linked the program. Everything went well, 0 errors; 0 warnings.
Still, CW did not have the new class included in its list.
I deleted the ".ncb", the ".opt" (and some other files), compiled and linked the program again, and still the new class was not included in CW.
Finally, I deleted the ".clw" file, compiled and linked the program again, but this time CW asked if I wanted to create a new CW file. I clicked OK, and behold! the new CW file this time included the new class I had a few moments ago created.
Is this just another one of CW quirks that I'll have to live with, or did I do something wrong it didn't like?
Thanks.
William
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do you have any anti-virus apps running? i've seen this kind of thing with Norton. it makes life exciting.
-c
Green's Law of Debate:
Anything is possible if you don't know what you're talking about.
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Yes, I do have anti-virus software running continuously!
My machine is heavily equiped with anti-virus software, including Norton's enterprise edition.
Thanks for the tip. I appreciate it.
William
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According to MSDN, TransparentBlit is not supported in 95 (or i mis-read it  ).
Anyone know of a way to support this under 95? ie updates, dll etc
Thanks
Robert Cannell
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