Back in C++ I used to do:
Lets get this straight:
Qt IS C++ code!
Just like you don't differentiate between STL or boost and c++, so you don't with Qt.
Do you understand the concept of a library?

Should i do read it line by line or store it directly to variable.
Reading line by line is still just reading.
Storing in something else - they are not exclusive.

suppose in Qt there are lots of overloaded functions and classes that let you do this
What is 'this'?
Reading from a file?
Storing your data in an array?
All of the above?

And you are right - there are a lot of Classes in Qt.
but I haven't found them yet
Here is the full list:
http://doc.trolltech.com/4.7/classes.html

It seems you are aware of streams, as you have posted in your code.
So why not start for example by searching for streams in the Qt documentation?
If you are aware of streams, you probably are also aware of vectors, which you could also look in the Qt docs.
Usually the Qt classes have very sensible name, so searching for "file" in the class list will give you some good hits to what you might be looking for, if for example you need some file handling classes.
Qt has many STL classes reimplemented, take the time to read the documentation.