Incompatible pointer type when referencing the method.

[artwaw]

@jsulm but how?
Sure, I can move that callback outside the class. That also means I'd need to somehow move the QDataStream outside... I am not sure if I know how to safely and correctly design that.
PdfWizard is of QMainWindow, so everything is in it.

[J.Hilk]

@artwaw

I think you could simply use a lambda stored in an auto and capture a reference to your QDataStream and/or class instance in general.

not the cleanest solution, but should work.

[artwaw]

@J-Hilk Thank you but I don't know how to do that. I use lambdas with connect when needed, but my c++ skill is not enough.

I could get away with making QDataStream a public member of QMainWindow but I feel dirty just thinking of it.

[J.Hilk]

@artwaw said in Incompatible pointer type when referencing the method.:

Thank you but I don't know how to do that. I use lambdas with connect when needed, but my c++ skill is not enough.

this is untested:

FPDF_FILEWRITE writer;
    writer.version = 1; 
    auto myFunction = [this](FPDF_FILEWRITE* pThis, const void* pData, unsigned long size)->int {
        Q_UNUSED(pThis)
        return writerStream.writeRawData(static_cast<const char*>(pData), size);
}
    writer.WriteBlock = &myFunction;
    bool result = FPDF_SaveAsCopy(document, &writer,FPDF_INCREMENTAL);

[artwaw]

@J-Hilk Thank you, will test.

[artwaw]

@J-Hilk
PdfWizard.cpp:358:25: error: incompatible pointer types assigning to 'int (*)(struct FPDF_FILEWRITE_ *, const void *, unsigned long)' from '(lambda at PdfWizard.cpp:350:24) *'

[jsulm]

@artwaw said in Incompatible pointer type when referencing the method.:

but how?

Well, you need to get access to the instance. One way is to make the class a singleton.

[artwaw]

@jsulm said in Incompatible pointer type when referencing the method.:

make the class a singleton

I went here https://www.oreilly.com/library/view/c-cookbook/0596007612/ch08s10.html

This is doable, I think, but at this point I am coming to the conclusion that it would be better to redesign my approach by wrapping all interactions with PDFium into a separate class and only expose methods that do stuff I need.

There is so much I don't know how to do yet...

[J.Hilk]

@artwaw oops, my bad, a lambda can only be converted to a function pointer if it does not capture

The closure type for a lambda-expression with no lambda-capture has a public non-virtual non-explicit const conversion function to pointer to function having the same parameter and return types as the closure type’s function call operator. The value returned by this conversion function shall be the address of a function that, when invoked, has the same effect as invoking the closure type’s function call operator.

Reference link

[artwaw]

I managed to construct a singleton class to handle the I/O and so it works. Thank you all for the input, it is always great to learn from you!

[mpergand]

I know nothing about Poppler but for defining a C callback method in C++, this method need to be static.
See this post

[artwaw]

@mpergand thank you but:

• I stated previously that I work with PDFium this time, as Poppler doesn't offer edits;
• I managed to work around without using static method: maybe not the nicest solution around but works.

At any rate I made a note of your comment in case I need to revisit this godawful file format known as PDF in the future.