Why does select(QTextCursor::BlockUnderCursor) include an extra junk character? - c++

Question

Windows 7 SP1
MSVS 2010
Qt 4.8.4
I am using QTextCursor to grab each block's text. I use select(QTextCursor::BlockUnderCursor) to grab the text and then go to the next block with movePosition(QTextCursor::NextBlock). But when I again select(QTextCursor::BlockUnderCursor) I get an extra junk character in the QString and the anchor has moved to the end of the previous block.
Using this for text.txt:
A
B
This code's comments walks through the issue and asks the questions:
#include <QTGui>
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QMainWindow* window = new QMainWindow;
QTextEdit* editor = new QTextEdit(window);
QTextDocument* document = new QTextDocument(window);
editor->setDocument(document);
QFile file("test.txt");
if (file.open(QFile::ReadOnly | QFile::Text))
editor->setPlainText(file.readAll());
QTextBlock block = document->begin();
QTextCursor* cursor = new QTextCursor(document);
int pos = cursor->position(); // = 0
int anchor = cursor->anchor(); // = 0
cursor->select(QTextCursor::BlockUnderCursor);
pos = cursor->position(); // = 1
anchor = cursor->anchor(); // = 0
QString text = cursor->selectedText(); // = "A"
int size = text.size(); // = 1
cursor->movePosition(QTextCursor::NextBlock);
pos = cursor->position(); // = 2
anchor = cursor->anchor(); // = 2
cursor->select(QTextCursor::BlockUnderCursor);
pos = cursor->position(); // = 3
anchor = cursor->anchor(); // = 1 Why not 2?
text = cursor->selectedText(); // "B" in debugger
// but text.at(0) = junk & test.at(1) = "B"
size = text.size(); // = 2 Why? Why not 1?
return app.exec();
}

Answer 1

It is not junk. The first character includes the U+2029 paragraph separator (HTML: 
 PSEP). In other words, selecting the block includes the starting paragraph separator. The first block doesn't have a starting SEP. Therefore, need to exclude the first character if one wants to extract the text alone of subsequent blocks.

Answer 2

The navigation values has to do with the nature of a QTextBlock, and how navigating by block and what is determined by BlockUnderCursor. The documentation gives some insight into this:
http://doc.qt.digia.com/main-snapshot/qtextblock.html#details
Here is another part of the documentation seemed helpful to me:
http://doc.qt.digia.com/main-snapshot/qtextblockformat.html#details
I haven't experimented with what you found, but here are some of my thoughts on it:
In some ways I think of it like pressing Ctrl+Up or Ctrl+Down in Windows in a MS Word document. Some of it may have to do with the line endings you are using. "\r\n" v. "\n". I know that sometimes the "eof" character is weird to work with. Some documents and formats require a new line before the end of file character.
Hope that helps.