The sample code shows how dangerous it can be to blindly copy a QString to a QUrl. Tested with Qt 5.1.1 and Qt 5.2.0 on Ubuntu.

copy-qstring-to-qurl-trap.cpp

QUrl dst;
QUrl src = QUrl::fromLocalFile("aPictureFile.jpg");
qDebug() << "INITIAL STATE";
qDebug() << "Source: " << src;
qDebug() << "Destination URL: " << dst;
dst = src;
qDebug() << "END STATE 1";
qDebug() << "Destination URL: " << dst;
qDebug() << "Destination local file: " << dst.toLocalFile();
dst = src.toLocalFile();
qDebug() << "END STATE 2";
qDebug() << "Destination URL: " << dst;
qDebug() << "Destination local file: " << dst.toLocalFile();

// INITIAL STATE
// Source:   QUrl( "file:aPictureFile.jpg" )
// Destination URL:   QUrl( "" )
// END STATE 1
// Destination URL:   QUrl( "file:aPictureFile.jpg" )
// Destination local file:  "aPictureFile.jpg"
// END STATE 2
// Destination URL:   QUrl( "aPictureFile.jpg" )
// Destination local file:  ""