Re: Joy of this, Joy of that

On 27/11/2024 16:33, Rich wrote:

The Natural Philosopher <tnp@invalid.invalid> wrote:

On 27/11/2024 01:48, Rich wrote:

The only two guarantees given in that paragraph are:
>
1) if ptr was returned by one of the malloc's, the space referenced by
     ptr is deallocated (albeit only for the first call of free(ptr), per
     the second sentence);
and
2) if ptr is NULL, nothing occurs.

>
Exactly.  The result of anything else is implementation dependent on the
library.
>
One might write a free that says 'look at our list of allocated blocks,
compare with the pointer and if no match do nothing'
>
Or one that says  'look at our list of allocated block compare with the
pointer and if no match, segfault'
>
I am not au fait with the internal of 'free()' so I cannot comment as to
why the first is not always the case.

 I can hazzard a guess.  The time taken to perform the search, or the
effort needed to maintain an "index structure" to perform an optimized
search, plus the time for the optimized search, was felt to be
excessive and wasteful when the "spec" says "don't ever do this".
 

Look I don't know how memory allocation and de allocation is done
but my instinct would be to hold a long list of pointers to allocated blocks.  Possibly in order of the allocated addresses, which would make allocating a new block a case of finding the first gap in the list that is [required blocksize] and inserting a new list element, and de allocation a question of searching the list for a matching allocation, and deleting it from the list.
It would be trivial to get to the end of the list and discover that that was the end, and, with no match found simply ignore the free call
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Climate Change: Socialism wearing a lab coat.