Hi Ben, Please see my responses below:
On Mon, Aug 22, 2011 at 3:01 PM, Ben Stott <[email protected]> wrote: > > > > On Mon, Aug 22, 2011 at 1:36 PM, asif saeed > > > > > I read the following tutorial yesterday - it creates class > > > > members on stack > > > > > - that is, it does not make them pointers and allocate them > > > > using new(): > > > > > > > > > > http://www.fltk.org/doc-2.0/html/example3.html > > > > > > > > > > I have also gone through examples that create members on > > > > heap - that is, > > > > > the members are pointers - not values/objects. I have read > > > > in docs that > > > > > Fl_Group automatically deletes the children, that you add, > > > > upon exit. What > > > > > is the difference between creating members on stack and on > > > > heap? Don't you > > > > > think creating them on stack will automatically release > > > > them that could > > > > > cause Fl_Group to release non-existing memory? > > > > > > Why do you think that would happen? > > > > The docs say that the groups automatically add whatever children get > created > > after them - they automatically issue a begin or something like that - > > apparently each widget adds itself to the group in its constructor. I > read > > that while reading about creating members on heap using new(). I also > read > > that the groups automatically delete the children. Now if you create > > children on stack then they will first be released via stack pop and then > > the group will delete them - and here the group will delete something > that > > will have already been deallocated through stack unwinding. > > > > So, two things: > 1) You've posted a link to fltk2.0 documentation -- and judging by some of > your comments in a few threads, seem to be referencing 2.0 classes -- but > are talking about Fl_Group and the 1.3 counterparts. Yes, you're right. I posted an fltk-2.0 link but the example applies to 1.3 as well. The really cool thing about C++ is that you can't call operator delete on > any variable that's not dynamically allocated. { int i; delete &i; //this works but blows up big-time, of course. But compiler doesn't check it at compile time. } > You also don't have your deallocation ordering strictly correct. The stack > unwind will always be the last-constructed order - so if you declare a > Fl_Group above a Fl_Widget, the Fl_Widget will be destructed *before* the > Fl_Group. > Ya, I know - I call it DMB (DUMB) destruction - (D)erived classes, (M)embers and (B)ase. I probably mis-typed something in a hurry. Hopefully this answers your question. The group will never delete anything > that has been deallocated via the stack, and vice versa. That's exactly what I wanted to know. But the question remans: when should I create member widgets as pointers and when should I create them as direct object members (non pointers, that is)? Ben > Best, Asif _______________________________________________ fltk mailing list [email protected] http://lists.easysw.com/mailman/listinfo/fltk
