Pointer to QByteArray as LPBYTE

Rory_1

I am attempting to provide color management for my Qt image viewing app using the library lcms2. I have everything working except pulling the icc profile from a jpeg file. I have extracted the icc segment in a QByteArray called iccBuf.

lcms2 has a function:
cmsOpenProfileFromMem(const void * MemPtr, cmsUInt32Number dwSize);

"Opens an ICC profile which is entirely contained in a memory block. Useful for accessing embedded profiles. MemPtr must point to a buffer of at least dwSize bytes. This buffer must hold a full profile image. Memory must be contiguous."

I have seen code that supplies the MemPtr parameter as a LPBYTE but I cannot convert the QByteArray address to LPBYTE. I have tried:

reinterpret_cast<const void*>(&(iccBuf).data()[0])
and
(unsigned char*)G::iccBuf.data()

but these do not work.

It appears I need to convert char* to uchar*

Any advice would be greatly permitted.

Thanks in advance!

SGaist

Hi,

What exact error are you getting ?

Rory_1

@sgaist The function cmsOpenProfileFromMem is returning a nullptr indicating failure.

Snippet:

QByteArray iccBuf;
// load iccBuf with file icc data segment
quint32 iccLen = iccBuf.length();  
LPBYTE buf = (unsigned char*)iccBuf.data();
hInProfile = cmsOpenProfileFromMem(iccData, iccLen);
// output from qDebug:
iccBuf.data() = 0x7ff61053e5c0    buf = 0x1a2811400c8

Christian Ehrlicher

I've no documentation for cmsOpenProfileFromMem() but how should it suppose to work when you pass a pointer to data with a length of zero?

Rory_1

@christian-ehrlicher Apologies - I quickly threw together the use case. The variable iccLen is defined in the code as the length of iccBuf. I have tweaked the code above to show this.

Christian Ehrlicher

@rory_1 said in Pointer to QByteArray as LPBYTE:

The variable iccLen is defined in the code as the length of iccBuf.

... which is still zero since you have an empty QByteArray

Rory_1

@christian-ehrlicher Yes I know. I was trying to state in my comments that I obtained the byte array and was continuing. I agree that was not clear. I have solved the issue - my test jpg file had a non-compliant embedded profile.

Many thanks for taking the time to help!