[Qt-interest] binaries in Ubuntu versions

[Oliver.Knoll at comit.ch]

Harald Fernengel wrote on Monday, December 01, 2008 1:25 PM:

>> ...
>> Generally? I remember one "glitch" where the Trolls accidentally made
>> a default argument (something like "int foo = 0") non-default. That
>> broke the binary compatibility in the early 4.x days between two Qt
>> versions (or was it even in the late 3.3.x days? Can't remember).
>
> Default arguments are not part of the ABI.
>
> If you know about any ABI changes in the Qt 4 series, please let us
> know.

I obviously seem to remeber the same "binary incompatibility" as Arnold has in mind, see his post:

"Apart from one minor release in the Qt4 cycle, Qt is binary compatible."

And AFAIK it had to to with an argument in some Qt method had a default value, as in:

  QFoo::theMethod(int bar = 42);

which was accidentally removed in the next minor release, as in:

  QFoo::theMethod(int bar);

Now older Qt applications which relied on the default value of '42' now would provide "random memory garbage" for the argument 'bar' at best, which clearly breaks binary compatibility. So I don't quite understand what you meant with "Default arguments are not part of the ABI", because they clearly are.

And it had been Trolltech itself notifying people on this list about this issue ;) I think it was between 4.0.1 to 4.0.2 or so, can't remember (and can't remember which class was affected).

Cheers, Oliver