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On 9/17/22 01:25 Greg Ercolano wrote:
On 9/16/22 14:48, roger tunnicliffe
wrote:
Thx for the reply (sorry can't see your name).
I am wondering then what would be the use cases for each
particular syntactical version. ie.
When and why would i use this code....
Fl_Button fltkButton(25, 20, 70, 50, "button1");
noting it requires fltkButton.labelsize(12);
as opposed to this code....
Fl_Button *fluidButton = new Fl_Button(25, 80, 70,
50, "button2");
noting it requires
fltkButton->labelsize(12);
Probably no good reason, other than it's shorter.
There may be cases where you want a C++ object to be deleted when
the current scope is left. One (mostly internal) FLTK example is
Fl_Widget_Tracker which is usually allocated on the stack (a local
variable) so it is automatically deleted at the end of the function
or method.
If
you're new to C++, I'd suggest always using 'new' to create
FLTK widgets so you don't have to worry about widgets going
out of scope prematurely.
It should be noted that the pointer you use when allocating with
`new` would also go out of scope eventually and thus it can't be
used later unless saved as Kevin described in another reply.
An important point here is that the "automatic parenting mode" of
FLTK usually adds a widget to the current group (window) so you can
"forget" the pointer because you will likely not use it later.
Working example code with comments below:
#include <FL/Fl.H> #include <FL/Fl_Window.H> #include <FL/Fl_Button.H>
int main(int argc, char **argv) { // allocate window on stack: scope/lifetime is main() Fl_Window window(240, 140, "main window");
{ // introduce a local block (scope)
// allocate button b with operator new Fl_Button *b = new Fl_Button(20, 20, 200, 100, "Hello, world!");
// use the pointer b b->color(FL_YELLOW);
// pointer b goes out of scope but the window keeps a pointer // to the button and the widget will not (yet) be destroyed }
window.end(); // end automatic parenting window.show(argc, argv); return Fl::run();
// the window 'window' will be deleted after main() and // its destructor will also delete the button }
If you would allocate the button on the stack in the local scope
rather than using `new` it would be deleted at the end of the block
and it would be removed from the window at that time (try this).
I didn't bother to add a button callback, you need to close the
window with the window's close ('X') button or hit the 'Esc' key to
end the program.
I hope this helps.
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