Peek on QTextStream

peek, qt, qtextstream, seek

Solution

You peek from `QIODevice`, but then you read from `QTextStream`, that's why peek works only once. Try this:

while (!s.atEnd()) {
      ++i;
      qDebug() << "Peek" << i << s.device()->peek(3);
      QByteArray v = s.device()->readLine ();
      qDebug() << "Word" << i << v;
}

Unfortunately, `QIODevice` does not support reading single words, so you would have to do it yourself with a combination of peak and read.

Problem

I would like to peek the next characters of a QTextStream reading a QFile, in order to create an efficient tokenizer. However, I don't find any satisfying solution to do so. ``` QFile f("test.txt"); f.open(QIODevice::WriteOnly); f.write("Hello world\nHello universe\n"); f.close(); f.open(QIODevice::ReadOnly); QTextStream s(&f); int i = 0; while (!s.atEnd()) { ++i; qDebug() << "Peek" << i << s.device()->peek(3); QString v; s >> v; qDebug() << "Word" << i << v; } ``` Gives the following output: ``` Peek 1 "Hel" # it works only the first time Word 1 "Hello" Peek 2 "" Word 2 "world" Peek 3 "" Word 3 "Hello" Peek 4 "" Word 4 "universe" Peek 5 "" Word 5 "" ``` I tried several implementations, also with QTextStream::pos() and QTextStream::seek(). It works better, but pos() is buggy (returns -1 when the file is too big). Does anyone have a solution to this recurrent problem? Thank you in advance.

Original source