Bug in Qt Quarterly 31 Matching Parentheses with QSyntaxHighlighter

netzlab

Hey guys,

I'm writing on a little code editor and I found this page:
http://developer.qt.nokia.com/doc/qt-4.8/widgets-codeeditor.html#suggestions-for-extending-the-code-editor

In the last paragraph stands a link to a parenthesis-matching-algo. So I included the algorithm to my application, but the algorithm has a bug. The function matchRightParenthesis occurs an error, because if it calls itself, it passed '0' as a second parameter, but that's wrong.

I've corrected the Algo quick and dirty:

@bool matchLeftRoundParenthesis(QTextBlock currentBlock, int index, int numRightParentheses);
bool matchRightRoundParenthesis(QTextBlock currentBlock, int index, int numLeftParentheses, bool firstTime = false);@
@void TabWidget::matchParentheses()
{
QListQTextEdit::ExtraSelection selections;
setExtraSelections(selections);

TextBlockData *data = static_cast<TextBlockData *>(textCursor().block().userData());

if (data) {
    QVector<ParenthesisInfo *> infos = data->parentheses();

    int pos = textCursor().block().position();
    for (int i = 0; i < infos.size(); ++i) {
        ParenthesisInfo *info = infos.at(i);

        int curPos = textCursor().position() - textCursor().block().position();
        if (info->position == curPos - 1 && info->character == '(') {
            if (matchLeftParenthesis(textCursor().block(), i + 1, 0))
                createParenthesisSelection(pos + info->position);
        }

else if (info->position == curPos - 1 && info->character == ')') {
if (matchRightParenthesis(textCursor().block(), i - 1, 0, true))
createParenthesisSelection(pos + info->position);
}
}
}
}

bool TabWidget::matchRightParenthesis(QTextBlock currentBlock, int i, int numRightParentheses, bool firstTime)
{
TextBlockData *data = static_cast<TextBlockData *>(currentBlock.userData());
QVector<ParenthesisInfo *> parentheses = data->parentheses();

if(!firstTime) //Set i to the end of the parentheses list.
i = parentheses.size()-1;
int docPos = currentBlock.position();
for (; i > -1 && parentheses.size() > 0; --i) {
ParenthesisInfo *info = parentheses.at(i);
if (info->character == ')') {
++numRightParentheses;
continue;
}
if (info->character == '(' && numRightParentheses == 0) {
createParenthesisSelection(docPos + info->position);
return true;
} else
--numRightParentheses;
}

currentBlock = currentBlock.previous();
if (currentBlock.isValid())
    return matchRightParenthesis(currentBlock, 0, numRightParentheses);

return false;

}@

Maybe it could be corrected in the example code?
Regards netzlab

dangelog

It can if you submit a patch with the correction. :-)

You can also simply leave a docnote on that specific page stating the correction, though. That'll be appreciated.

netzlab

I want to add a docnote, but I haben't enough points to do that. :)

dvillalobos

Nice post. Helps me a lot.

Wouldn't it be nice to have a Qt native Code Editor like the one in QtCreator?