Progress of reading the file

[ModeZt]

I read the input text file line by line.

dataFile = new QFile(fileName);
dataFile->open(QIODevice::ReadOnly | QIODevice::Text);
dataStream = new QTextStream(dataFile);
while( !dataStream->atEnd() ) {
    line = dataStream->readLine();
    ...
}

dataFile = new QFile(fileName);
dataFile->open(QIODevice::ReadOnly | QIODevice::Text);
dataStream = new QTextStream(dataFile);
while( !dataStream->atEnd() ) {
    line = dataStream->readLine();
    ...
}

To copy to clipboard, switch view to plain text mode 

The file is > 200Mb.
I need to update a progress bar while i analize the lines.
I was going to use

100 * currentLine / numberOfLines

100 * currentLine / numberOfLines

To copy to clipboard, switch view to plain text mode 

but how do i get the number of lines in the file?..

Thx!