asked on

Getting a CBitmap from a HBITMAP, using FromHandle()

I need to get a CBitmap from a HBITMAP, and to be able to delete my CBitmap again, when I need to.

My code looks like this:

class SomeClass
{
CBitmap *m_bmpBitmap;

SomeFunction();
~SomeClass();
};

SomeClass::SomeFunction()
{
HBITMAP hBitmap;

hBitmap=(HBITMAP) LoadImage(NULL, "BitmapName.Bmp", IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE | LR_CREATEDIBSECTION | LR_DEFAULTSIZE);
m_bmpBitmap=new CBitmap();
m_bmpBitmap=CBitmap::FromHandle(hBitmap);
}

SomeClass::SomeClass()
{
delete m_bmpBitmap;
}

My problem is that when I come to the Destructor, and want to delete the m_bmpBitmap again, my program crashes, becourse the CBitmap is attached to a HBITMAP, and I don't know how to detach it again.

How do delete my m_bmpBitmap in a proper way (So that it won't cause the program to crash) ?

Norbert

Not rearly clear what your problem is but
You should initialisize pointers to 'valid' value
Constructor:
SomeClass::SomeClass()
{
m_bmpBitmap=NULL;
}
Destructor:
SomeClass::~SomeClass()
{
if(m_bmpBitmap)
delete m_bmpBitmap;
}
now SomeFunction
SomeClass::SomeFunction()
{
HBITMAP hBitmap;

hBitmap=(HBITMAP) LoadImage(NULL, "BitmapName.Bmp", IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE | LR_CREATEDIBSECTION | LR_DEFAULTSIZE);
//m_bmpBitmap=new CBitmap(); NOT NEEDED and Produces MEMORY LEAKS !!!!
if(m_bmpBitmap)
delete m_bmpBitmap;
m_bmpBitmap=CBitmap::FromHandle(hBitmap);
}

Some OtherFunction
SomeClass::OtherFunction()
{
if(bmpNoMoreNeeded)
{
if(m_bmpBitmap)
{
delete m_bmpBitmap
m_bmpBitmap=NULL;
}
}
}

that should prevent double deleting the same pointer

chensu

Regarding Norbert's code, don't delete m_bmpBitmap returned by CBitmap::FromHandle. It will be deleted automatically at idle time. So, the pointer returned by CBitmap::FromHandle may be invalid outside SomeClass::SomeFunction(). You can do it in this way.

class SomeClass
{
CBitmap *m_bmpBitmap;

SomeFunction();
~SomeClass();
};

SomeClass::SomeFunction()
{
HBITMAP hBitmap;

hBitmap=(HBITMAP) LoadImage(NULL, "BitmapName.Bmp", IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE | LR_CREATEDIBSECTION | LR_DEFAULTSIZE);
m_bmpBitmap=new CBitmap();
m_bmpBitmap->Attach(hBitmap);
}

SomeClass::~SomeClass()
{
::DeleteObject(m_bmpBitmap->Detach());
delete m_bmpBitmap;
}

To be safer, remember to check the return value of each function called.

Morten from Eliten

ASKER

Hey, chensu !
Propose that as an answer, and you've earned yourself 30 points.

That was great !

ASKER CERTIFIED SOLUTION

chensu

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