get size of malloc'd object

[Frank Adams]

In article <2233 at peora.UUCP> jer at peora.UUCP writes:
>[Frank Adams]
>> Depends on what you mean by "portable".  Certainly, it is possible to use
>> this number in an implementation-dependent way; but there are natural and
>> non-implementation-dependent ways to use the information.  E.g., if one is
>> allocating character strings and one of them grows, one can try to fit the
>> expanded string into the allocated size, and only reallocate (and reset all
>> the pointers to the data) if it won't fit.
>
>Well, actually it depends on some other factors, just fairly abstract ones
>(and thus debatable).  According to the System V manual, "Malloc returns a
>pointer to a block of at least _size_ bytes suitably aligned for any use."
>
>The problem is that, unless the definition is constrained more, it makes
>it impossible to prove a program that uses the "actual size allocated"
>correct.

So constrain the definition more.  It isn't written in stone.  I dare say
that there is no system in existence that would fail under the assumption
that the actual size allocated fits in a long -- probably none would fail
assuming an int.

Compared to the total task of dealing with the C environment in such a way
that correctness proofs become possible, this is a very tiny issue, easily
dealt with.

Frank Adams                           ihnp4!philabs!pwa-b!mmintl!franka
Multimate International    52 Oakland Ave North    E. Hartford, CT 06108