[Qt-interest] Passing QList<QStringList> as arguments

[John Weeks]

On Aug 24, 2010, at 2:50 PM, Eric Clark wrote:

> No because QStringList is not the same as QList<QString>.  
> QStringList inherits QList<QString>, it is not a typedef. If a  
> function expects a QStringList you need to use a QStringList because  
> up-casting (if that is a word) is not valid in c++. You can,  
> however, downcast a QStringList to a QList<QString> because it is a  
> QList<QString>. Hope this makes sense, it did to me…

I've always heard "down cast" as meaning getting a derived class  
pointer from a base class, and "up cast" as the opposite. But you  
don't hear "up cast" because a pointer to a derived class in C++  
simply *is* a pointer to the base class, no cast required.

C++ does have dynamic_cast<>() that allows you (if you have run-time  
type information enabled) to get a pointer to a derived class if you  
hold a pointer to the base class. You have to be ready for an  
exception to be thrown if the pointer you hold really isn't a pointer  
to the derived class, though.

Regards, John Weeks

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