How to format the selected text in a QTextEdit by pressing a button

I want to format a selected text in a QTextEdit by clicking a button. For axample I want to make it bold if it is not-bold, or not-bold if it is bold. Please help me with an example.

EDIT:

Actually I have found already a code - qt demo for text editor which does what I need:

void
MyTextEdit::boldText(bool isBold) //this is the SLOT for the button trigger(bool)
{
    QTextCharFormat fmt;
    fmt.setFontWeight(isBold ? QFont::Bold : QFont::Normal);
    mergeFormatOnWordOrSelection(fmt);
}

void
MyTextEdit::mergeFormatOnWordOrSelection(const QTextCharFormat &format)
 {
     QTextCu开发者_如何学JAVArsor cursor = m_textEdit->textCursor();
     if (!cursor.hasSelection())
         cursor.select(QTextCursor::WordUnderCursor);
     cursor.mergeCharFormat(format);
     m_textEdit->mergeCurrentCharFormat(format);
 }

But I can't understand what returnes the textCursor() method, and how the merging of properties is being done? Just some formats are being changed, some of them stay constant. How mergeCharFormat function understands what to change and what to leave as is. Please explain me just these 2 things. Thanks.

The textCursor() returns a textCursor that contains the position of the cursor you use in the textEdit, see QTextCursor in Qt classes. So by selecting the text that is contained by the cursor start and end position, you have the text that is currently highlited.

As for the mergeCharFormat, I guess that it is used to apply a new state (bold, italic, underlined) and to keep the existing ones. Say your text is already underlined and you apply bold, you would want to keep both.

Hope this helps.