Re: Simple question on Pointers
"Alan Carre" <alan@twilightgames.com> wrote in message
news:eqvVSieVJHA.4888@TK2MSFTNGP02.phx.gbl
See, there's actually 3 relevant objects involved here which I will
simply call:
A [an "inifile" wrapper class]
B [the map of filenames to actual inifiles (see below)]
C [the actual file data to be shared by instances of A
- cached in memory, copied via smart pointer]
Now when you create an instance of A, it will go and access a static
member of C which will in-turn call up B (the singleton) to try to
find a C* to bind with A. If a match is found it returns an existing
C*, otherwise creates a new one. Same old boring stuff everyone does.
So that means that B will certainly outlive the first instance of C,
but that's all we know so far.
No, we don't know that. Apparently, C is dynamically created with new.
It would have to be explicitly destroyed with delete. The compiler
doesn't enforce any particular destruction order between globals and
heap objects. Your code will have to arrange for that.
If A in this scenario is a global variable, then B will outlive A.
Perhaps this is what you were trying to say.
Here's the key difference: We can build ourselves a global A without
having to construct a B.
Didn't you just say: when you create an instance of A, it will go and
access a static member of C which will in-turn call up B. So which way
is it - does A require a B, or does it not?
Here are the 2 ways:
1. Declare an empty one (no lookups)
2. Invoke it's copy constructor through a "temporary 'A'"
So all you have to do is for A's constructor to request a B even if it
doesn't strictly need to at the time (that is, when constructed empty).
So as you can see, although 'sect' is a static global, it's creation
is invoked via a temporary 'A' (TwInifile) which in turn allocates (if
necessary) a 'C*' (pointer to data) which may (or may not) construct
'B'. If it happens that B gets constructed here, then it occurs
*before* the copy constructor is invoked and hence 'sect' is
scheduled to destruct *after* 'B' (the map of filenames to C*'s).
I don't follow. If B is constructed before sect, then it would be
destroyed after sect, no?
--
With best wishes,
Igor Tandetnik
With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925