Am 23.06.2014 um 19:13 schrieb Till Oliver Knoll <till.oliver.kn...@gmail.com>:
> ...
> And I /still/ think that was exactly one of the (many) selling points of
> using the Qt Meta Object over the RTTI, because the later is /not/ guaranteed
> to work "across DLLs" when it comes to dynamic casting... it even sais (said)
> so in the Qt docs, IIRC.
Here's a link that I quickly found which seems to confirm that at least at
/some/ point in the past /some/ compilers did not support "dynamic casting
across library boundaries using RTTI":
http://stackoverflow.com/questions/21314557/why-does-qt-reimplement-rtti-in-qobject-cast-event-type-etc
"Historically, with some compilersdynamic_cast failed across shared library
boundaries."
(And no, the Stack Overflow answer wasn't given by me ;))
I think what Thiago meant by the "single library constraint" was simply: "make
sure that the generated meta info code is only compiled and linked into one
library (preferably the one which also implements the class), and not into
several (-> multiple symbols!)" - E.g. by accidentally add the class header to
several *.pro HEADER entries, such that it gets mocced and compiled several
times (but why would you do that?).
Given the fact that the moccing is all automated with qmake (and assuming that
you don't rename or #include the generated files in some "funny way" which
might lead to pitfalls) I don't remember having ever problems with that.
The only problem I do remember however is that the generated code was not "DLL
exported": in order to keep the "export table" to a minimum I usually only
export the (public/protected) methods (members) of a class that I really want
to be callable from outside the library (you know, that "__dllexport /
__dllimport" stuff - which also provides somewhat another "module" level of
visibility, besides public/protected/private).
For QObject derived classes however using the Qt Meta Object system (and having
the Q_OBJECT macro properly defined in their class declaration) one needs to
export the /entire/ class. Otherwise the generated code (giving access to the
meta system) would not be "visible" from outside the library (-> linker error).
That's the only "pitfall" that I remember. But maybe I am just overlooking the
most obvious pitfall here?
Cheers,
Oliver
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