how come I can not use the Release( ) methord of CComPtr? - C / C++ / MFC Discussion Boards

bob1697217-Apr-06 5:46

17-Apr-06 5:46

I was flipping through Meyer's "Effective C++" this morning trying to remember how to do something and I noticed he's not directly concerned with "efficiency" (per se) but he does get to the heart of portable C++ and mentions "efficiency" quite a bit as a secondary argument for many program design recommendations. I remembered your post and thought I'd add this comment in hindsight.

Some tips will yield you more efficient code directly and some will point out where designing for robustness, clarity, and caution will yield more maintainable code at the cost of efficiency but these same tips can be reversed to point you to places where you could squeeze out some more speed.

The book is a keeper in so many ways it isn't funny so if you don't already have it. Get it. It's also listed here at CP as a recommended book by the masses (or at least whoever put that list together)

Take care and good luck in your competition.

Re: Optimizing

El Corazon16-Apr-06 15:30

El Corazon

16-Apr-06 15:30

hint_54 wrote:
I need a few c++ code optimizing tips. Anybody knows where I can find good ones?

As already mentioned, measure first. Always keep in mind the 80/20 rule (depending on who is talking this might even be referred to as a 90/10 rule -- I prefer 80/20 because that usually assumes you have not optimized yet, Wink | ;)

): 80% of the time is spent in 20% of the code, when you have optimized you might actually reach the 90/10.

Optimize the code that is A) called the most often B) more time is spent in the code. These could be two different areas, "A" could be a short module that even saving 2% of the overhead within will make a difference because of how often it is called. "B" could be a long routine that could be redesigned to spend less time within.

Reduce redundancy. If you call cos(angle) 10 times for the same angle, consider making a local variable to hold the result and reuse the result 10 times rather than calculate the cosine of the angle 10 different times for the same angle.

That may sound obvious, but you would be surprised at how many people don't think about it. Also don't replace a single point of reduncany without a check, usually it is still faster to allocate the local variable and store the result, but for some CPU math instructions it is easier to calculate twice than to allocate the memory use it and deallocate at the end.

That is why measuring is extremely important. You will discover faster ways yourself, especially in algorithms, because you will get to know your own code better.

_________________________
Asu no koto o ieba, tenjo de nezumi ga warau.
Talk about things of tomorrow and the mice in the ceiling laugh. (Japanese Proverb)

Bitmap pixels

nikhilsai16-Apr-06 3:06

nikhilsai

16-Apr-06 3:06

How to calculate the Red, gree, Blue values of each and every pixel (of say around 50000 pixles) in a bitmap?

Re: Bitmap pixels

eli1502197916-Apr-06 3:24

eli15021979

16-Apr-06 3:24

Hi,

You should use CDC::GetPixel() which returns the RGB value of a specific
pixel of the bitmap.

Regards,
Eli

Re: Bitmap pixels

bob1697216-Apr-06 15:49

bob16972

16-Apr-06 15:49

that should be your last resort as it is very slow

Re: Bitmap pixels

Hamid_RT16-Apr-06 6:33

Hamid_RT

16-Apr-06 6:33

Hi nikhilsai,
maybe it is some helpful to you

You can use CImage for load bitmap and use GetPixel that retun COLORREF

Re: Bitmap pixels

MANISH RASTOGI16-Apr-06 18:39

MANISH RASTOGI

16-Apr-06 18:39

GetRValue(rgb value)
GetGVaiue(rgb value)
GetBValue(rgb value)

how come I can not use the Release( ) methord of CComPtr?

ewighell16-Apr-06 2:41

ewighell

16-Apr-06 2:41

whenever I use it, following "build error" shows up:

F:\hu\DD\DetailDesign\ProfileFeatureCmd.cpp(2850) : error C2248: 'Release' : cannot access private member declared in class 'ATL::_NoAddRefReleaseOnCComPtr<struct sketchpoint="">'
d:\program files\microsoft visual studio\vc98\atl\include\atlbase.h(420) : see declaration of 'Release'

Thank you very much!!!

-------------------
I am learning C++ and English

Re: how come I can not use the Release( ) methord of CComPtr?

RChin16-Apr-06 3:06

RChin

16-Apr-06 3:06

Instead of calling the underlying interface's Release function, call the class's Release method.

So, instead of :

<br />
pMyInterface->Release();<br />

Try:

<br />
pMyInterface.Release();<br />

<EDIT>
But the ATL class will do this automatically for you when it goes out of scope, so you don't need to explicitly do this<
;EDIT>

I Dream of Absolute Zero

-- modified at 9:07 Sunday 16th April, 2006

Re: how come I can not use the Release( ) methord of CComPtr?

Stephen Hewitt16-Apr-06 4:21

Stephen Hewitt

16-Apr-06 4:21

This is by design. The reason in that when you call Release through a smart pointer you've probably just introduced a bug into your code - So ATL disallows it. He's some code which shows why this is the case:

{
     CComPtr<IDispatch> spDisp;
     CoCreateInstance(CLSID_SomeObject, NULL, CLSCTX_ALL, IID_IDispatch, reinterpret_cast<void**>(&spDisp));
     // At this point there is one reference to the object held by our smart pointer.
     spDisp->Release();
     // ATL will not allow this. If it did, after this the reference count is zero but the
     // smart pointer still "thinks" it owns a reference.
}
// At this point the smart pointer will attempt to <code>Release</code> its reference.
// As mentioned earlier the reference count is actually zero so this will probably end
// in disaster (if you're lucky, quickly).

Steve

Re: how come I can not use the Release( ) methord of CComPtr?

ewighell16-Apr-06 15:25

ewighell

16-Apr-06 15:25

The reason why I have been using the operator "->" is that I always treat a smart pointer as a pointer, now I think it through that it is a object class CComPtr<...>

Thank you all very much!!!

-------------------
I am learning C++ and English

Multiple instances of a DLL

Virtek16-Apr-06 2:38

Virtek

16-Apr-06 2:38

Hi.

I was wonder how can I set multiple instances of one dll file,

see the following:

<br />
<br />
typedef void type_SetX(int x);<br />
typedef int type_GetX();<br />
<br />
type_SetX *SetX;<br />
type_GetX *GetX;<br />
<br />
HINSTANCE h1 = LoadLibrary("foo.dll");<br />
HINSTANCE h2 = LoadLibrary("foo.dll");<br />
<br />
SetX = (type_SetX *)GetProcAddress(h1, "SetX");<br />
GetX = (type_GetX *)GetProcAddress(h1, "GetX");<br />
<br />
SetX(5);<br />
Print( GetX() ); // GetX returns 5 as it should.<br />
<br />
// Now i'll set X on h2 instance<br />
<br />
SetX = (type_SetX *)GetProcAddress(h2, "SetX");<br />
<br />
SetX(8); // It's OVERWRITING h1, because h1=h2, they point to the same instace !!!<br />
<br />
Print( GetX() ); // Because of the overwrite, GetX returns 8, as I wanted it to return 5...<br />

The var X inside the dll is not static of course.
Any idia how can I manage multiple instances of the same dll ?

Thanks,

David

-- modified at 8:39 Sunday 16th April, 2006

Re: Multiple instances of a DLL

eli1502197916-Apr-06 3:21

eli15021979

16-Apr-06 3:21

Hi David,

I'm not sure , but have you tried to use different function pointers for each instance of the DLL?

Regards,
Eli

Re: Multiple instances of a DLL

Virtek16-Apr-06 4:19

Virtek

16-Apr-06 4:19

Hi Eli.

Yes, but it doesn't matters because LoadLibrary() always return a pointer to the same instance.
I wrote a simple test code:

<br />
<br />
HINSTANCE h1 = LoadLibrary("Foo.dll");<br />
HINSTANCE h2 = LoadLibrary("Foo.dll");<br />
<br />
bool IsSame = (h1 == h2);<br />
<br />

well, IsSame = true...
Maybe the rule states: One instance of a DLL-File per process.
And my only way is to inject it to a thread...

Thanks,

David

Re: Multiple instances of a DLL

Michael Dunn16-Apr-06 6:14

Michael Dunn

16-Apr-06 6:14

Virtek wrote:
HINSTANCE h1 = LoadLibrary("Foo.dll");
HINSTANCE h2 = LoadLibrary("Foo.dll");

bool IsSame = (h1 == h2);

You're seeing the correct behavior, that's how DLLs work. The second LoadLibrary() sees that the DLL is already loaded, so it just increments the reference count.

--Mike--
Visual C++ MVP Cool | :cool:

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finding files with a certain extension

SWDevil16-Apr-06 2:26

SWDevil

16-Apr-06 2:26

Hi,

I need to find all files in a certain directory that are in the format of: file.001, file.002, etc (the numbers in the file extensions can go up to infinity...).
I am using the functions FindFile and FindNextFile to do this (my code is below). The problem is that in the same directory there might also be files named file.x or file.y (for example) which I don't need to find.
I only need the files with the number extensions.
Is there a way to do this?

this is my code:
sSearchPath.Format("file.*");
BOOL bWorking = f.FindFile(sSearchPath);
while (bWorking)
{
bWorking = f.FindNextFile();
CString strFileName = f.GetFileName();
}

Thanks

Re: finding files with a certain extension

shortwave16-Apr-06 2:51

shortwave

16-Apr-06 2:51

I dont know if this code work with but this what I used
int i=0;
WIN32_FIND_DATA info;
HANDLE hp;
sprintf(fileFound, "%s\\*.tga", folderPath);
hp = FindFirstFile(fileFound, &info);
if(hp== INVALID_HANDLE_VALUE)
return;
do
{
sprintf(fileFound,"%s\\%s", folderPath, info.cFileName);
// DeleteFile(fileFound);

i++;
}while(FindNextFile(hp, &info));
FindClose(hp);
ShowMessage(i);

Re: finding files with a certain extension

SWDevil16-Apr-06 2:58

SWDevil

16-Apr-06 2:58

I don't understand, are u looking for all files that have a .tga extension?

Re: finding files with a certain extension

shortwave16-Apr-06 3:03

shortwave

16-Apr-06 3:03

yes I do

Re: finding files with a certain extension

SWDevil16-Apr-06 3:09

SWDevil

16-Apr-06 3:09

Thanks for your help - but that's not what I need...
I need to look for a files that have the same file name each time, but have different extensions.
For Example, in my directory there are the files:
file.001
file.002
file.x
file.y

so, I don't need to find the files file.x or file.y. I only need to find the files that have an extension that consists of numbers.
The problem is that when I search for files in the format: "file.*", it finds the files named file.x and file.y which I don't need.

Re: finding files with a certain extension

shortwave16-Apr-06 3:19

shortwave

16-Apr-06 3:19

ok for(.............etc.)
sprintf(fileFound, "%s\\file.00%.1d
",ARRAYOFCONST((folderPath,i)) );
now you can search for ectintions
from 001 to 009

-- modified at 9:20 Sunday 16th April, 2006

Re: finding files with a certain extension

SWDevil16-Apr-06 3:32

SWDevil

16-Apr-06 3:32

yes - but I don't know what the maximum number the extension could have. There could be a file named file.9999 for instance..
so I can't search until infinity. That's my problem.

Maybe there is a way to check if the extension contains only numbers or something like that. Do you know?

Re: finding files with a certain extension

shortwave16-Apr-06 3:57

shortwave

16-Apr-06 3:57

I dont remember the function name but try this

sSearchPath.Format("file.*");
BOOL bWorking = f.FindFile(sSearchPath);
int j = 0, i++;
while (bWorking)
{
CString strFileEx = ExtractFileExt(f.GetFileName());
while(strFileEx [j] != '\0' )
{
if(!((int)strFileEx [j] >= (int)'0' && (int)strFileEx [j]<='9'))
i++;
}
if(i>0)
//do what you want to do
bWorking = f.FindNextFile();

}

-- modified at 9:57 Sunday 16th April, 2006

Re: finding files with a certain extension

SWDevil16-Apr-06 4:07

SWDevil

16-Apr-06 4:07

Thanks!
But what is the function "ExtractFileExt"? my code doesn't recognise it. do I need an include for it or something?

Re: finding files with a certain extension

David Crow17-Apr-06 3:51

David Crow

17-Apr-06 3:51

Why not just use PathFindExtension()?

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