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From: Gennaro Prota (gennaro_prota_at_[hidden])
Date: 2002-11-17 13:09:26

On Sun, 17 Nov 2002 18:22:20 +0100, Thorsten Ottosen
<nesotto_at_[hidden]> wrote:

>Yes, but note that having both is less fortunate. Either we agree that
>library writers check preconditions and then
>clients don't or we agree that clients check preconditions and library
>writers don't. One reason that C is such
>a pain in the *** to use is because its the cliets responsibility to check
>conditions , e.g.
>int * i = malloc( sizeof( i ) );
>assert( i );

Well, apart from the C-style void*->int* conversion and the curious
sizeof(i) instead of sizeof(int), weren't you speaking of
preconditions? :-)

Anyhow one of the reasons why C++ (or C if you want to talk about it)
is the way we all know is that it does its best to avoid unnecessary
costs: "you do not pay for what you don't use". In a situation where
you are absolutely sure that no precondition is violated you don't
want the library to check that for you. C++ programmers are not the
kind of guys who like range-checking on vector::operator[] when they
have something like:

  for (std::size_t i = 0; i < v.size(); ++i)
      std::cout << vect[i] << '\n';

That's way generally libraries don't check in 'non-debug mode'. OTOH,
it's obvious that strictly speaking there's no "debug mode" built-in
into the language either so your problem of "over-checking" (if it is
a problem) is actually in the scope of the contract between the user
and the library itself (That is: library xyz can tell you that, when
NDEBUG is not defined, it asserts on precondition violations for you).

Maybe, we could encourage library writers to document such a fact?


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