How can I do the following..

**Dual-Catfish** · 04-29-2002

I have CDib Class here which loads DIBs (device independant bitmaps) It has a member funtion ::Load(const char *pszFilename) which takes a filename and loads the DIB from it.
I'm trying to modify the class to include a function ::LoadIndirect(const char *pszData) to load bitmaps based on character data sent.

The load function uses the following expression:
cf.Read( &BFH, sizeof( BITMAPFILEHEADER );
Where cf is of type CFile and BFH is BITMAPFILEHEADER.
How is it doing this, or shall I say, how can I do this with a chunk of data instead of a file?

It opens the file, and reads data in to the address of BFH. Alright. So I tried:

Code:

	BITMAPFILEHEADER BFH;
	unsigned char *pBFHTemp = new unsigned char[sizeof(BITMAPFILEHEADER)];
	for (int i = 0; i < sizeof(BITMAPFILEHEADER); i++)
	{
		pBFHTemp += pszData[i];
	}
	&BFH = pBFHTemp;
	delete[] pBFHTemp;

But I get the following error: DIB.cpp(188) : error C2440: '=' : cannot convert from 'unsigned char *' to 'struct tagBITMAPFILEHEADER *'
Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast

All I want to do is take data, and place it at the address of BFH, how can I do this?

**ygfperson** · 04-29-2002

the best i can come up with, with the information you provided, is a syntax error. chances are high it's not this, but it's all i could think of.
1) can char* be +=?
and btw, what is pszdata?
2) does &BFH = pBFHTemp work?

**Dual-Catfish** · 04-29-2002

1) can char* be +=?
and btw, what is pszdata?
2) does &BFH = pBFHTemp work?

1) That was a typo, it's actually string.
2) pszData is a bitmap file, passed to the function. It's just unsigned char, which I have to parse and load.
3) No, &BFH = pBFHTemp is the line that generates the error

**kwigibo** · 04-29-2002

I thought I read this already. Or has it changed since last time?

Anywayz

&BFH = pBFHTemp

is the operator overloaded? And how come the reference is at the front there?

kwigibo

**fyodor** · 04-29-2002

Are you sure that &BFH is an lvalue?

**ygfperson** · 04-29-2002

why not just make a pointer of type BITMAPFILEHEADER and use that instead of BFH?

**Dual-Catfish** · 04-30-2002

>is the operator overloaded?
I'm not sure.. I assume so, seeing as I get no error...
>And how come the reference is at the front there?
Because I wan't to put the data at 'the address of' BFH. Simply assigning it wouldn't work, as it has many member variables.

The data is structured in such a way, that if I could insert it into the memory space of BFH, all the member variables would get the correct value... but I've tried different variations of this and I cannot get this working

**swoopy** · 04-30-2002

Code:

	BITMAPFILEHEADER *BFH;
	unsigned char *pBFHTemp = new unsigned char[sizeof(BITMAPFILEHEADER)];
	for (int i = 0; i < sizeof(BITMAPFILEHEADER); i++)
	{
		pBFHTemp += pszData[i];
	}
	BFH = (BITMAPFILEHEADER *) pBFHTemp;

And the call would be:

cf.Read( BFH, sizeof( BITMAPFILEHEADER ));

**Sebastiani** · 04-30-2002

Well I dont know much about the BITMAPWHATEVERHEADER struct but you cannot do:

&BFH = pBFHTemp;

...because (a) that is an illegal assignment and (b) BFH is a structure ( or perhaps a typedef for a pointer to one ) and pBFHTemp is a char pointer!

So if it is the data ( the "chars" ) you want, then simply look at the definition of the BITMAPWHATEVERHEADER structure where you will most certainly find a "char *" ( or LPSTR, or similar ) which points directly to the data!

Now if the originators of windows were sensible folk, this variable would be named something like "unsigned char *data", but seeing how this is not usually the case, it will probably be named "LPSTR lCmfsHddlDibHerKraut" or similar.

**Dual-Catfish** · 04-30-2002

>cf.Read( BFH, sizeof( BITMAPFILEHEADER ));
But that's not the call :/
The call is cf.Read( &BFH, sizeof(BITMAPFILEHEADER));
The definition of BITMAPFILEHEADER can be found here:
http://msdn.microsoft.com/library/de...tmaps_62uq.asp

I have no idea how cf.Read() does it :/

**swoopy** · 04-30-2002

That's because it takes a pointer to a BITMAPFILEHEADER. Since:
BITMAPFILEHEADER *BFH;
is already a pointer to a BITMAPFILEHEADER, then:

cf.Read( BFH, sizeof( BITMAPFILEHEADER ));

**Dual-Catfish** · 04-30-2002

This is MY load function..
In the other load function, BFH was not a pointer, and it was used as cf.Read(&BFH, sizeof(BFH));

In my function, I need to replicate this behavior.. read data from a larger chunk of data, the size of BFH and store it at the address of BFH.

Allow me to post code..

Code:

BOOL CDib::Load( const char *pszFilename )
{

	CFile cf;

	// Attempt to open the Dib file for reading.
	if( !cf.Open( pszFilename, CFile::modeRead ) )
		return( FALSE );

	// Get the size of the file and store
	// in a local variable. Subtract the
	// size of the BITMAPFILEHEADER structure
	// since we won't keep that in memory.
	DWORD dwDibSize;
	dwDibSize =
		cf.GetLength() - sizeof( BITMAPFILEHEADER );

	// Attempt to allocate the Dib memory.
	unsigned char *pDib;
	pDib = new unsigned char [dwDibSize];
	if( pDib == NULL )
		return( FALSE );

	BITMAPFILEHEADER BFH;

	// Read in the Dib header and data.
	try{

		// Did we read in the entire BITMAPFILEHEADER?
		if( cf.Read( &BFH, sizeof( BITMAPFILEHEADER ) )
			!= sizeof( BITMAPFILEHEADER ) ||

			// Is the type 'MB'?
			BFH.bfType != 'MB' ||

			// Did we read in the remaining data?
			cf.Read( pDib, dwDibSize ) != dwDibSize ){

			// Delete the memory if we had any
			// errors and return FALSE.
			delete [] pDib;
			return( FALSE );
			}
		}

	// If we catch an exception, delete the
	// exception, the temporary Dib memory,
	// and return FALSE.
	catch( CFileException *e ){
		e->Delete();
		delete [] pDib;
		return( FALSE );
		}
	
	// If we got to this point, the Dib has been
	// loaded. If a Dib was already loaded into
	// this class, we must now delete it.
	if( m_pDib != NULL )
		delete m_pDib;

	// Store the local Dib data pointer and
	// Dib size variables in the class member
	// variables.
	m_pDib = pDib;
	m_dwDibSize = dwDibSize;

	// Pointer our BITMAPINFOHEADER and RGBQUAD
	// variables to the correct place in the Dib data.
	m_pBIH = (BITMAPINFOHEADER *) m_pDib;
	m_pPalette =
		(RGBQUAD *) &m_pDib[sizeof(BITMAPINFOHEADER)];

	// Calculate the number of palette entries.
	m_nPaletteEntries = 1 << m_pBIH->biBitCount;
	if( m_pBIH->biBitCount > 8 )
		m_nPaletteEntries = 0;
	else if( m_pBIH->biClrUsed != 0 )
		m_nPaletteEntries = m_pBIH->biClrUsed;

	// Point m_pDibBits to the actual Dib bits data.
	m_pDibBits =
		&m_pDib[sizeof(BITMAPINFOHEADER)+
			m_nPaletteEntries*sizeof(RGBQUAD)];

	// If we have a valid palette, delete it.
	if( m_Palette.GetSafeHandle() != NULL )
		m_Palette.DeleteObject();

	// If there are palette entries, we'll need
	// to create a LOGPALETTE then create the
	// CPalette palette.
	if( m_nPaletteEntries != 0 ){

		// Allocate the LOGPALETTE structure.
		LOGPALETTE *pLogPal = (LOGPALETTE *) new char
				[sizeof(LOGPALETTE)+
				m_nPaletteEntries*sizeof(PALETTEENTRY)];

		if( pLogPal != NULL ){

			// Set the LOGPALETTE to version 0x300
			// and store the number of palette
			// entries.
			pLogPal->palVersion = 0x300;
			pLogPal->palNumEntries = m_nPaletteEntries;

			// Store the RGB values into each
			// PALETTEENTRY element.
			for( int i=0; i<m_nPaletteEntries; i++ ){
				pLogPal->palPalEntry[i].peRed =
					m_pPalette[i].rgbRed;
				pLogPal->palPalEntry[i].peGreen =
					m_pPalette[i].rgbGreen;
				pLogPal->palPalEntry[i].peBlue =
					m_pPalette[i].rgbBlue;
				}

			// Create the CPalette object and
			// delete the LOGPALETTE memory.
			m_Palette.CreatePalette( pLogPal );
			delete [] pLogPal;
			}
		}
	
	return( TRUE );

}

My (not working) Load funtion..

Code:

BOOL CDib::LoadIndirect(const char *pszData)
{
	if (pszData == NULL)
	{
		return (FALSE);
	}

	// Get the size of the file and store
	// in a local variable. Subtract the
	// size of the BITMAPFILEHEADER structure
	// since we won't keep that in memory.

	DWORD dwDibSize;
	dwDibSize = strlen(pszData) - sizeof(BITMAPFILEHEADER);

	unsigned char *pDib;
	pDib = new unsigned char [dwDibSize];	// Attempt to allocate the Dib memory.

	if (pDib == NULL)
	{
		return (FALSE);
	}
	BITMAPFILEHEADER BFH;

	string sBmpHeader;
	for (int i = 0; i < sizeof(BITMAPFILEHEADER); i++)
	{
		sBmpHeader += pszData[i];
	}
	BFH = sBmpHeader;

	string sBmpData;
	for (i = sizeof(BITMAPFILEHEADER); i < strlen(pszData); i++)
	{
		sBmpData += pszData[i];
	}
	pDib = sBmpData.c_str();

	if (strlen(sBmpData) != dwDibSize || sBmpHeader != sizeof(BITMAPFILEHEADER) || BFH.bfType != 'MB')
	{
		delete [] pDib;
		return (FALSE);
	}

	// If we got to this point, the Dib has been
	// loaded. If a Dib was already loaded into
	// this class, we must now delete it.
	if (m_pDib != NULL)
	{
		delete m_pDib;
	}

	// Store the local Dib data pointer and
	// Dib size variables in the class member
	// variables.
	m_pDib = pDib;
	m_dwDibSize = dwDibSize;

	// Pointer our BITMAPINFOHEADER and RGBQUAD
	// variables to the correct place in the Dib data.
	m_pBIH = (BITMAPINFOHEADER *) m_pDib;
	m_pPalette =
		(RGBQUAD *) &m_pDib[sizeof(BITMAPINFOHEADER)];

	// Calculate the number of palette entries.
	m_nPaletteEntries = 1 << m_pBIH->biBitCount;
	if( m_pBIH->biBitCount > 8 )
		m_nPaletteEntries = 0;
	else if( m_pBIH->biClrUsed != 0 )
		m_nPaletteEntries = m_pBIH->biClrUsed;

	// Point m_pDibBits to the actual Dib bits data.
	m_pDibBits =
		&m_pDib[sizeof(BITMAPINFOHEADER)+
			m_nPaletteEntries*sizeof(RGBQUAD)];

	// If we have a valid palette, delete it.
	if( m_Palette.GetSafeHandle() != NULL )
		m_Palette.DeleteObject();

	// If there are palette entries, we'll need
	// to create a LOGPALETTE then create the
	// CPalette palette.
	if( m_nPaletteEntries != 0 ){

		// Allocate the LOGPALETTE structure.
		LOGPALETTE *pLogPal = (LOGPALETTE *) new char
				[sizeof(LOGPALETTE)+
				m_nPaletteEntries*sizeof(PALETTEENTRY)];

		if( pLogPal != NULL ){

			// Set the LOGPALETTE to version 0x300
			// and store the number of palette
			// entries.
			pLogPal->palVersion = 0x300;
			pLogPal->palNumEntries = m_nPaletteEntries;

			// Store the RGB values into each
			// PALETTEENTRY element.
			for( int i=0; i<m_nPaletteEntries; i++ ){
				pLogPal->palPalEntry[i].peRed =
					m_pPalette[i].rgbRed;
				pLogPal->palPalEntry[i].peGreen =
					m_pPalette[i].rgbGreen;
				pLogPal->palPalEntry[i].peBlue =
					m_pPalette[i].rgbBlue;
				}

			// Create the CPalette object and
			// delete the LOGPALETTE memory.
			m_Palette.CreatePalette( pLogPal );
			delete [] pLogPal;
			}
		}
	
	return( TRUE );


}

**swoopy** · 04-30-2002

I'm thinking this would work:

Code:

	BITMAPFILEHEADER *BFH;

	string sBmpHeader;
	for (int i = 0; i < sizeof(BITMAPFILEHEADER); i++)
	{
		sBmpHeader += pszData[i];
	}
	BFH = (BITMAPHEADER *) sBmpHeader.c_str();

	string sBmpData;
	for (i = sizeof(BITMAPFILEHEADER); i < strlen(pszData); i++)
	{
		sBmpData += pszData[i];
	}
	pDib = sBmpData.c_str();

	if (strlen(sBmpData) != dwDibSize || sBmpHeader != sizeof(BITMAPFILEHEADER) || BFH -> bfType != 'MB')

**swoopy** · 04-30-2002

> if (strlen(sBmpData) != dwDibSize || sBmpHeader != sizeof(BITMAPFILEHEADER) || BFH -> bfType != 'MB')

This part of the if() statement looks questionable though:
sBmpHeader != sizeof(BITMAPFILEHEADER)

sBmpHeader is a string, so you need the string length of sBmpHeader, right?

**Dual-Catfish** · 05-01-2002

Just ignore that part for now, it doesn't work yet, as I can't get get the data in the correct places anyway ;(

Once I can replicate the behaviour of that line, I'll be on my way... but until then, I'll sit and cry about it.

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