Why is the lambda crashing my program?

[ayanda83]

Hi there guys, I am new to C++11 expressions. I got a lambda below and it crashes my program.

void Joburg_Page::connect_to_HTML_tags(bool ok)
{
    QString docTitle;
 
    this->runJavaScript("document.title"
                        "}", [&docTitle](const QVariant &data){docTitle = data.toString();});
 
    qDebug() << docTitle <<endl;
}
}

void Joburg_Page::connect_to_HTML_tags(bool ok)
{
    QString docTitle;
    
    this->runJavaScript("document.title"
                        "}", [&docTitle](const QVariant &data){docTitle = data.toString();});
    
    qDebug() << docTitle <<endl;
}
}

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Why is it necessary that I must declare docTitle is a member of the class before the above code works?

[anda_skoa]

runJavaScript is asynchronous, the scope of connect_to_HTML_tags() has ended before the lambda is being executed.
docTitle has ceased to exist by the time it is accessed.

Cheers,
_