QUrl (mis)usage: appendix, avoid automatic cast from QString

As I was introducing in the former entry QUrl (mis)usage, the direct creation of a QUrl from a QString should be avoided in any software that is not trying to smartly guess what a user input should lead to.

So, going directly to the ham, to avoid mistakes due to automatic conversions from QString to QUrl, I encourage the usage of the QT_NO_URL_CAST_FROM_STRING macro. The only thing you have to do is adding a line to your qmake project file like this:

# Avoid automatic casts from QString to QUrl. Dangerous!!!
DEFINES += QT_NO_URL_CAST_FROM_STRING

Or add it directly to the compilation line, like this

g++ ... -DQT_NO_URL_CAST_FROM_STRING ...

As I was pointing in my previous post, the usage of QUrl::fromLocalFile(QString) and QUrl::fromEncoded(QByteArray, QUrl::StrictMode) is recommended when dealing with QString and QUrl, but committing mistakes is a human condition so it is pretty easy to end passing a QString as a parameter to some API expecting a QUrl, or assigning a QString to a QUrl with the “=” operator through the C++ automatic cast mechanism which is implemented in the QUrl class. That’s why forbidding these automatic casts in our code is of such importantance.

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