How to get the line height of a QTextBlock?

[therefore]

Windows 7 SP1
MSVS 2010
Qt 4.8.4

Given this code:

#include <QTGui>
 
    int main(int argc, char *argv[])
    {
    QTextDocument* text_document = new QTextDocument("testing");
    QTextBlock text_block = text_document->begin();
    qDebug() << text_block.text() << text_block.blockFormat().lineHeight()
    << text_block.blockFormat().lineHeightType();
    }

#include <QTGui>
     
    int main(int argc, char *argv[])
    {
    QTextDocument* text_document = new QTextDocument("testing");
    QTextBlock text_block = text_document->begin();
    qDebug() << text_block.text() << text_block.blockFormat().lineHeight()
    << text_block.blockFormat().lineHeightType();
    }

To copy to clipboard, switch view to plain text mode 

The console displays:

"testing" 0 0

Question: Why doesn't lineHeight return "the LineHeight property for the paragraph"? The lineHeightType is set for single spacing.

Even trying:

qDebug() << text_block.text() << text_block.layout()->boundingRect().height();

qDebug() << text_block.text() << text_block.layout()->boundingRect().height();

To copy to clipboard, switch view to plain text mode 

gives me zero.