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The Testfunction returns myClass also.
newclass doesn't exist past the end of testfunction, so the function returns a copy of it... Temporary copy needs constructing, and (drumroll) destructing.
Try adding another member to myClass, and a constructor which assigns a random value to it. Then also spit it out in the destructor. See how its actually different myClass instances getting killed.
As to the avoidance? That all depends on what you were really trying to do. What you have posted is a very artificial example to show the "double" destructing, it doesn't show what you were trying to do when you ran into this issue.
And just in case this is homework, as least I've only done 50% of your work.
Iain.
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well, no it's no homework. I'm well aware of the fact that the copy-call is run for the object that went out of scope...
To make my example less artificial:
In gsl a matrix need allocation of memory (alloc) and freeing the memory, of course.
I tried to write a matrix-class which does the allocation in the constructor and which does the freeing in the destructor.
Now I wrote an operator function for the multiplication:
CMatrix CMatrix::operator *(const CMatrix& factorMatrix);
when I try to return the resulting matrix the destructor is called and the memory freed thus the matrix deleted and cannot be assigned with any operation like the operator=...
better?
zqueezy
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The "extra" destructor you're getting is because you're being nice and elegant and writing a * operator, which (quite correctly) returns an instance (albeit a temporary one) on CMatrix.
If the constructor / destructor is "expensive", then you're going to have to do it a different way.
class CMatrix
{
public:
....
BOOL Multiply (CMatrix const &lhs, CMatrix const &rhs)
{
if (!ValidToDoThisMaths (lhs, rhs))
return FALSE;
....
return TRUE;
}
....
};
void main ()
{
CMatrix A,B,C;
A.Create (blah);
B.Set (blah);
C.Multiply (A,B);
C.DoStuff ();
}
Its less elegant, but it would solve your problem.
It would also lose the ability to do:
D = A * B * C
but frankly, matrices are enough of a pain to work with [ (n x m) * (m x n) etc ] that that's probably not a huge loss.
I hope that helped,
Iain.
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zqueezy wrote: Allright... actually there shouldn't be any destructor called BEFORE the cin.get().
Of course it should.
zqueezy wrote: The Destructor is somehow called for the return value and I don't know why...
Because newClass went out of scope, and the destructor must be called in that case.
zqueezy wrote: is there a way of not calling the destructor here?
Rewrite the function like this:
void myClass::Testfunction(myClass& obj)
{
obj.val = 7;
}
Create the object before calling it, and pass it as the argument.
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when I do the whole thing as reference... why is the destructor called anyways... isn't the reference just an address?
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zqueezy wrote: when I do the whole thing as reference... why is the destructor called anyways
No, it is not.
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Ach, I'm weak.
Below is a copy of a =operator function, where you can see the return type is a reference to object, rather than the object. This allows you to dasiy chain loads of =s together.
RgbQuad &operator=(RgbQuad &r)
{
rgbRed = r.rgbRed;
rgbGreen= r.rgbGreen;
rgbBlue = r.rgbBlue;
return *this;
};
I hope that steers you in the right direction.
Iain.
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zqueezy wrote: The Destructor is somehow called for the return value and I don't know why...
The newClass object in your test function is created on the stack and so cannot be used by anyone once the function exits. So the compiler has to copy it into your B variable, then destroy the newClass object. I think you're getting two calls to the destructor because the compiler is copying the newClass object into a temporary "return value" object and then copying this one into the B variable. Google for something called "return value optimization" for info on how to get rid of this.
zqueezy wrote: is there a way of not calling the destructor here?
Nope. The newClass object *must* be destroyed (since it's on the stack).
zqueezy wrote: because I actually free some memory in my prog in the destructor
This is usually not the best way of designing things but if you absolutely have to do it like this, allocate the newClass object from the heap (using "new") and return a pointer to that.
I enjoy occasionally wandering around randomly, and often find that when I do so, I get to where I wanted to be [^].
Awasu 2.3 [^]: A free RSS/Atom feed reader with support for Code Project. 50% discount on the paid editions for CP members!
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I didn't want to do a heap allocation... for the reason of the easy-user interface (see my first reply) but perhaps... that's the only possibility.
thanx for all your help
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To give my end-solution:
I didn't know I had to create a Copy-Constructor for my class,
you need a copy-constructor for classes that allocate memory dynamically...
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Im using this method needless to say is not working and need some help.
void rotateb(Bitmap* image, HDC dc){<br />
Graphics graphics(dc);<br />
Bitmap* SrcBitmap1 = image;<br />
Color mc;<br />
<br />
int angle=45;
float radians=(2*3.1416*angle)/360; <br />
<br />
float cosine=(float)cos(radians); <br />
float sine=(float)sin(radians); <br />
<br />
float Point1x=(-SrcBitmap1->GetHeight()*sine); <br />
float Point1y=(SrcBitmap1->GetHeight()*cosine); <br />
float Point2x=(SrcBitmap1->GetWidth()*cosine-SrcBitmap1->GetHeight()*sine); <br />
float Point2y=(SrcBitmap1->GetHeight()*cosine+SrcBitmap1->GetWidth()*sine); <br />
float Point3x=(SrcBitmap1->GetWidth()*cosine); <br />
float Point3y=(SrcBitmap1->GetWidth()*sine); <br />
<br />
<br />
float minx=min(0,min(Point1x,min(Point2x,Point3x))); <br />
float miny=min(0,min(Point1y,min(Point2y,Point3y))); <br />
float maxx=max(Point1x,max(Point2x,Point3x)); <br />
float maxy=max(Point1y,max(Point2y,Point3y)); <br />
<br />
int DestBitmapWidth=(int)ceil(fabs(maxx)-minx); <br />
int DestBitmapHeight=(int)ceil(fabs(maxy)-miny);<br />
<br />
Bitmap* DestBitmap = new Bitmap(DestBitmapWidth, DestBitmapHeight);<br />
<br />
for(int x=0;x<DestBitmapWidth;x++) <br />
{ <br />
for(int y=0;y<DestBitmapHeight;y++) <br />
{ <br />
int SrcBitmapx=(int)((x+minx)*cosine+(y+miny)*sine); <br />
int SrcBitmapy=(int)((y+miny)*cosine-(x+minx)*sine); <br />
if(SrcBitmapx>=0&&SrcBitmapx<SrcBitmap1->GetWidth() && SrcBitmapy>= 0 && <br />
SrcBitmapy<SrcBitmap1->GetHeight()) <br />
{ <br />
SrcBitmap1->GetPixel(SrcBitmapx,SrcBitmapy,&mc);<br />
DestBitmap->SetPixel(x,y,mc);<br />
} <br />
} <br />
} <br />
<br />
graphics.DrawImage(DestBitmap,0, 0); <-- this does not <br />
}
Thank you
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what does it display? Try to set some pixels in destination bmp with some constatnt color to check if there is problem in rotation alghoritm or displaying
rrrado
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Also, if you aren't required to write the rotation code yourself, GDI+ will do it for you 
Mark
"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder
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hi
the GDI+ i find is not very precise Mark i mean the image center shifts, and you have to draw the image then rotate the DC then draw it again you end up with two images and a rotated DC lol
the method i posted is skipping the second for loop for some reason 
thanks for your replies... back to digging
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hmm I've found it to be precise. Controlling the image center is easy handled.
I'm not sure what you mean by rotating a DC and ending up with two images - It uses pretty much
the same technique you are using.
Check this out (if you want to ). This spins an image (in a window, so you can watch) around
its center point (like a propellor LOL) at 5 degree increments...
Gdiplus::Bitmap SrcBitmap(L"C:\\test.bmp", FALSE);
Graphics DstGraphics(*this);
REAL angle = 0.0f;
for (int i = 0; i < 200; ++i)
{
DstGraphics.ResetTransform();
DstGraphics.RotateTransform(angle);
DstGraphics.TranslateTransform(SrcBitmap.GetWidth() / 2.0f, SrcBitmap.GetWidth() / 2.0f, MatrixOrderAppend);
DstGraphics.DrawImage(&SrcBitmap, -((INT)SrcBitmap.GetWidth() / 2), -((INT)SrcBitmap.GetHeight() / 2),
SrcBitmap.GetWidth(), SrcBitmap.GetHeight());
angle += 5.0f;
if (angle >= 360.0f)
angle -= 360.0f;
}
"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder
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I am working on a large codebase on VC++ 6.0, which contains many unused functions. i.e. functions that are never called from anywhere else in the code. I would like to delete these functions.
Without having to run every possible scenario with some sort of code coverage tool, is there any possible way to find these functions? Currently all I can do is do a Find In Files on the function name and work it out.
Thanks for your help...
Cheers
d3m0n
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do you want to do that for your personal order? I mean the compiler sees which functions you use...
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Yes... it's sometimes confusing if you're changing a file, and there's a function in there with an obvious bug. There's no point trying to fix the bug if that function is totally redundant. Better to just remove it.
So I was wondering if there was a way to find every redundant function, so I don't waste my time looking at them.
Thanks.
Cheers
d3m0n
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[d3m0n] wrote: So I was wondering if there was a way to find every redundant function...
Doesn't the profiler tell you this?
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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I could never get the profiler to work. Enabled the option in the project settings but the [Build->Profile] menu is always disabled.
Might try again though if you think it would be useful for what I'm trying to do.
Thanks.
Cheers
d3m0n
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[d3m0n] wrote: Enabled the option in the project settings...
On the Link tab, you checked the Enable profiling checkbox?
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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Interesting this profiler, I did not know its existence but do not see a profiler anywhere neither in Build menu nor in the settings.
I use VS 2003. could you help please?
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Yup, and rebuilt like it says in MSDN 
Cheers
d3m0n
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Hi all,
I am capturing video from device and then rendering it in a Dialog Box window using RenderStream function by using the following piece of code:
CHECK_HRESULT(UnInitializeGraph());
CHECK_HRESULT(InitializeGraph(enmCAPTURE_GRAPH, hParent, hPreview));
CComPtr pCaptureFilter;
CHECK_HRESULT(AddFilterByName( CLSID_VideoInputDeviceCategory, bstrDeviceName, &pCaptureFilter));
CHECK_HRESULT(RenderStream(pCaptureFilter, PIN_CATEGORY_PREVIEW, MEDIATYPE_Video));
CHECK_HRESULT(GetGraphInterfaces());
and it is working fine.
Now suppose i don't want to use RenderStream given above and get the same functionality.I want to connect the individual filters by AddFilter function.
Actually i am trying to do that but i am not getting anything.
Please help me how should i proceed.
Thanks and Regards,
Mayank
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