Re: [Opencxx-users] How to identify objects?

[Grzegorz J. <ja...@he...>]

Hi,

On Mon, 31 May 2004 ch...@da... wrote:

> Hello all,
>
> I=B4m a newbie that have just discovered this great tool and have a
> question: it is possible to identify an object of a class?
>
> Let me explain: I want to implement a "log-able" class which would be mor=
e
> or less like the BeforeClass in the examples but, additionaly to identify
> the methods that are called, I want to identify  the parameters passed an=
d
> the object that have made the invocation in order to be able to
> reconstruct the computation.
>
> Imagine that have a class A and two objects belonging to this class, let
> say a1 and a2, how can I differenciate the invocation of the same method
> in each object? Can someone recommend a reference or give an idea?

(1) Do you want to add logging code at caller site or at callee site?

(2) Do you want to log identity of caller or callee? (In the first
    paragraph you write about caller object, in the second about the
    callee object).

(1)-caller, (2)-caller: use 'this' at call site.

(1)-caller, (2)-callee: add code to take callee address just before
    the call is made, e.g. instrument

       p[14].fun->Foo();

    like this:

       __logging_utility_log(p[14].fun, "Foo", "a", 5)->Foo("a", 5);

    and add

       template <class T> T* __logging_utility(T* p, /* other stuff */)
       {
           /* do actual logging, 'p' has identity of callee */
           return p;
       }

(1)-callee, (2)-caller: here you want calee to know at runtime who is the
    caller; as far as I know this cannot be done portably in C++ itself,
    so you either need to add some code on the caller's side or you
    need to use non-portable code to inspect the stack and find
    out the address of calling function (from which you can later
    figure out if it is a method of an object; if so, then
    it is likely to have object address as one of its arguments;
    this is all highly non-portable in terms of compiler and
    hardware, also optimization in some cases may affect the stack
    layout)

(1)-callee, (2)-callee: use 'this' at callee site.

One additional thing to watch for is that in class hierarchies with
multiple inheritance or with virtual inheritance one object may have many
valid addresses, so you have to normalize address obtained from 'this' by
casting to one of the least derived base classes. (Finding such class is
of course doable with OpenC++.)

I hope one of above variants is what you meant. The thing you are trying
to do (computation reconstruction) seems very interesting. Could you
elaborate a little bit on the context where you want to apply it?

Please let me know if you need more info.

BR
Grzegorz

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# Grzegorz Jakacki                       Huada Electronic Design #
# Senior Engineer, CAD Dept.              1 Gaojiayuan, Chaoyang #
# tel. +86-10-64365577 x2074               Beijing 100015, China #
# Copyright (C) 2004 Grzegorz Jakacki, HED. All Rights Reserved. #
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