Qt 5.5 setDevice() definition

Question

Okay, so I am writing a bit of software code (The it crowed guys will like that) using the Qt framework. I am curious if anyone out there can explain to me exactly how the setDevice() function within the QXmlStreamReader object class works. Using the Qt documentation I have come to the conclusion that it simply defines where the file that you want to stream is located, however; if this is the case, I am confused on why I need to open the file first before interacting with it. I am looking for a detailed understanding of how this works, I know that I should be able to figure it out, but I'm simply not that proficient yet at low level functionality within the c++ language. Thank you for any insight into this, you will really be helping me understand "how" the function works, which is very important to me.

Answer 1

The QXmlStreamReader class is a parser, meaning it can be used for any input source. Therefore, the input stream can be a file, but does not have to be. It could also be a QBuffer, a QTextStream, a QDataStream, or a host of other QIODevice subclasses. You have to open the file before passing it to the QXmlStreamReader because the class knows nothing about files. Code:

QFile file("somefile");
QXmlStreamReader reader;
if (file.open(QIODevice::ReadOnly))
    reader.setDevice(&file);
else
    /*FAILURE*/