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If you create them at the top of a method and then at some point during the method you return without using the variable, then you have created it for no reason. This could be expensive if the creation takes a long time, or uses a lot of memory, or if the object has several base classes for example.
Typically you should only create a variable at the point you are going to use it, this an help the compiler perform its optimisations too.
It also makes the code easier to use and less prone to bugs as you cannot accidentally change the variable before first use if you create it only where you need it.
You can also control the scope of the variable so it only exists for as long as it needs to.
regards,
Darka [ Xanya]
"I am not a slave to a god that doesn't exist."
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I guess I need to answer.
As has been said, in C, you have to do it at the top.
In C++, you don't, but some do, just because they learned from someone who does it that way, because they are used to it from C. Declaring the variable close to where you use it makes code more readable and less prone to bugs.
Christian Graus - Microsoft MVP - C++
Metal Musings - Rex and my new metal blog
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I learnt C++ first, then had to "backport" myself down to C when I got a job where the lead programmer was afraid of this new fangled OOP stuff.
You wouldn't believe how long it took me to realise that you had to pre-declare all your variables - there was much confusion before that! 
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Mr.Brainley wrote: Why is that ?
In C, you had to declare variables before any staments. In C++, you can declare variables at the point in which they are needed.
"Approved Workmen Are Not Ashamed" - 2 Timothy 2:15
"Judge not by the eye but by the heart." - Native American Proverb
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Hi all,
I am using VC++ 6.0 version. As a part of my project I had to use IHTMLInputElement Interface ( IHTMLInputElement *ptr ) . I added <mshtml.h> header file . But
Error is coming like this
"IHTMLInputElement' : undeclared identifier"
Why this is happening
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I hop you have checked this,
Header and IDL files Mshtml.h, Mshtml.idl
Minimum availability Internet Explorer 5.0
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Hello,
I am trying to examine MathType (Equations) OLE data.
My daughter Stav is totally blind. She is learning in the 10th grade and she needs books in Braille. I contacted the publisher of the Mathematics book she needs to learn from in order to produce it in Braille. I received a Word document containing embedded MathType equations.
This is a one time job, so if some of the steps should be done manually I do not care.
I finaly reached the conclusion that each equation data is kept in OLEDATA.MSO, MathType documents the binary data but I can not find it inside the file. Can someone help with the format of the file?
I saved the Word document as XML (Office 2003) and found all
//o:OLEObject[starts-with(@ProgID, 'Equation')]
But I do not know how to go from here
Thanks, Reuven
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Hello!
I have a problem with push-like checkboxes in my app under WinXP. When I embed manifest my push-like checkboxes look cute (round corners etc). But when mouse moves over that button it is hilighted. When mouse clicks it is still hilighted so the user cannot see check state (is button pushed or not). User is able to see the actual check state only when mouse is moved off the button. So in the case of push-like checkboxes this fancy hilighting is bad.
I want to turn off hilighting when button is in checked state.
The only way to do it (as I can see at the moment) is to subclass button window class. But the problem is I don't know to which messages to pay attention and what to do to stop hilghting.
What can you suggest?
------------
I love you
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How to declare checkbox and your problem is manifest ?
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I'm not sure I can understand your question.
By the way, I have mentioned manifest just to emphasize the fact that my buttons have native WinXP look-and-feel, including that evil (in my case of push-like checkboxes) hilighting.
------------
I love you
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Hello.
Im confused about const return types in functions.
To me it seems to say that the object that will be returned will be const, that is to say the object will not be modifiable. But I was messing around with it and I am able to modify the const return value  .
Could someone please explain const function return values.
Thank you.
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minkowski wrote: But I was messing around with it and I am able to modify the const return value .
Because you probably copied the return of the function into a local non-const variable. Something like this:
const int Fun()<br />
{<br />
return 10;<br />
}<br />
<br />
int main()<br />
{<br />
int Temp = Fun();<br />
Temp++;<br />
}
It is perfectly legal because you don't modify the return value of the function but you modify a copy of it (which is non-const).
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Thank you. Also is the same true for user defined objects? And also for returned references?
Thanks again.
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minkowski wrote: Also is the same true for user defined objects?
Yes, if you store it into another instance (the same way as in my previous example), you still make a copy of your object. And you can of course modify the copy without any problem (as it is constant).
minkowski wrote: And also for returned references?
A reference lets you return a member variable directly (for example in a function from a class, you return a reference to another member of your class). That lets you modify this variable directly. If you return a const reference, then you won't be able to modify the variable directly. Of course, you can still assign it into another variable (results in a copy of your member variable) that you can modify (it's a copy, so you can modify it, if it's non-const)
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minkowski wrote: But I was messing around with it and I am able to modify the const return value
Thats because, you must have removed its constness by assigning it to non-const variable.
OOps ! already answered by Cedric.
Same old thing, need to refresh frequently.
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Ok thanks guys. It makes sense now. I forgot about returning values makes a copy of the object (providing the return type is not a ptr or ref).
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Hi
How to print bitmaps in VC++ ?
thanks
KK
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One way is you can use of CreateDC or see StartDoc
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Hi everyone,
Now, if i will create a new MDI Child Window, i add a Template in the App
So, if i have 3 Child-Windows i must add 3 Templates ...
i add a template like this :
pDocTemplate = new CMultiDocTemplate(IDR_FCustomerSearch,
RUNTIME_CLASS(CMyProjectDoc), // I dont use Doc's
RUNTIME_CLASS(FCustomerSearch),
RUNTIME_CLASS(FCustomerSearchView));
if (!pDocTemplate)
return FALSE;
AddDocTemplate(pDocTemplate);
and i open the window like this:
void CMainFrame::OpenWindow(CString Name)
{
CString Cur;
CDocTemplate *Selected;
POSITION pos = theApp.GetFirstDocTemplatePosition();
while(pos != NULL) {
Selected = (CDocTemplate*)theApp.GetNextDocTemplate(pos);
ASSERT(Selected != NULL);
ASSERT(Selected->IsKindOf(RUNTIME_CLASS(CDocTemplate)));
Selected->GetDocString(Cur,CDocTemplate::docName);
if(Name == Cur) {
Selected->OpenDocumentFile(NULL);
}
}
}
Is it correct? or exists another, better possibility ?
Because if i have f.ex. 25 Child frames, i have a very long list of
Templates-Additions ...
Thanks 
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Are you confusing multiple documents with child frames ? Can you explain ?
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Thats possible LOL
Because i have all the programmation in my CFormView ( which is raccorded with a Dialog (
plus simplement) )
CMDIChildWnd with a CFormView and a CDocument ( not used )
So i have different CFormView's ... The CMDIChildWnd Object doesn't change normally
If i want open a new Child window, i need to do what?
Big thanks
-- modified at 7:15 Friday 20th October, 2006
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Hi,
I'm using the pdh library to monitor the allocated private bytes in order to find memory leaks in a big project. Now I realized that my class isn't leakfree itself, the constructor of my class does use up 104k, but the destructor only releases about 82k.
I copied the sources for my class to a new project and investigated the problem with Purify, and Purify tells me that there is a potentially memory leak of 16834 in one block allocated at the line
if(PdhAddCounter(m_hQuery,szCounterLine,0,&m_hCounter) != ERROR_SUCCESS)
and a memory leak of 2 blocks (I think that's for the 2 counters I monitor) for 314 bytes in the same line.
The help files of Visual C++ tell me that PdhCloseQuery(m_hQuery), which is called in the destructor, should free all resources belonging to the query and its contained counters, but even adding a loop with PdhRemoveCounter to remove the Counters (and freeing their memory) manually doesn't help. Purify still tells me of an potential memory leak of 16834 bytes in that line.
Now my question: what is causing this big amount of memory allocated at PdhAddCounter? I would have thought, that, if there's such a big amount associated to PdhQuery, it would be allocated at PdhOpenQuery. And how can this big memory block be freed again?
Hope anyone can help
Martin Dietz
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how to trim database items?
(trim left , right) or if you have any ideea please tell me !
Bravoone
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Did you ask this question on sql forum?
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