> But like Colombo...'just one more thing..' >
Actually - you asked two more questions...!
> button->callback(button_cb);
>
> why only one argument in this?
Because the second argument is defined as being optional (you can do
that in C++) so if you don't pass it in here, the compiler defaults it
to whatever you defined in the declaration of the method - NULL in this
case I think...
> int when = 0;
> Fl_Input *input[5];
>
> void toggle_cb(Fl_Widget *o, long v) {
> if (((Fl_Toggle_Button*)o)->value()) when |= v; else when
> &= ~v; //this line! (from 'when', i understand the part in the if())
OK, here we go; this is all standard C though, so a little time with a
decent C manual would possibly help.
At the top of the code fragment, "when" is declared as an int and set to
zero.
Later, after the if() we see:
when |= v;
Which expands to:
when = when | v; ( the |= notation is a shorthand form for
that...)
Which says that when becomes equal to the binary OR of when and v. Here,
when and v are bitmasks, with each bit having a specific meaning, and we
are OR'ing in new bits from v into when.
The else condition says:
when &= ~v;
Which similarly expands to:
when = when & (~v);
This means that when becomes equal to the binary AND of when and the
1-compliment (binary inversion) of v (the ~v notation means every 1
flipped to 0 and v.v.)
What this does is to *remove* from when any bits that are set in v.
Though you might have to write that out on paper to see it working!
> for (int i=0; i<5; i++) input[i]->when(when);
And here we have two different "when" items - the "when" that is a
member of input[i] and the one we have just created locally.
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