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Message-ID: <acHnnsjm3ngvwfnr@devuan>
Date: Tue, 24 Mar 2026 02:26:24 +0100
From: Alejandro Colomar <une+c@...jandro-colomar.es>
To: Charles Munger <clm@...gle.com>
Cc: sc22wg14@...n-std.org, Rich Felker <dalias@...c.org>,
musl@...ts.openwall.com
Subject: Re: [SC22WG14.35974] N3849 - Memory allocation with size feedback
v2, request for feedback
Hi Charles,
On 2026-03-23T17:58:55-0700, Charles Munger wrote:
> On Thu, Mar 19, 2026 at 4:16 PM Alejandro Colomar <une+c@...jandro-colomar.es> wrote:
> > | As far as developer ergonomics,
> > | there are costs and benefits to each approach.
> > | The functions that return a pointer
> > | (and use an out-param for the size)
> > | can assign the return value directly
> > | to where it’s likely to be consumed,
> > | to a non-`void` pointer.
> >
> > This is what makes it importantly safer.
> >
> > alx@...uan:~/tmp$ cat m.c
> > #include <stdlib.h>
> >
> > #define typeas(T) typeof((T){})
> > #define mallocarray(n, z) reallocarray(NULL, (n)?:1, z)
> > #define malloc_T(n, T) malloc_T_(n, typeas(T))
> > #define malloc_T_(n, T) ((void)0, (T *){mallocarray(n,
> > sizeof(T))})
> >
> > int
> > main(void)
> > {
> > long *p;
> >
> > p = malloc_T(42, long); // ok
> > free(p);
> >
> > p = malloc_T(42, int); // -Wincompatible-pointer-types
> > free(p);
> > }
> > alx@...uan:~/tmp$ gcc m.c
> > m.c: In function ‘main’:
> > m.c:16:11: error: assignment to ‘long int *’ from incompatible
> > pointer type ‘int *’ [-Wincompatible-pointer-types]
> > 16 | p = malloc_T(42, int); //
> > -Wincompatible-pointer-types
> > | ^
> >
> > Your variant is inherently unsafe, and can't be made type-safe in any
> > way. This is a non-starter, IMO.
> >
> If you're going to wrap it that way you can wrap it in a `static
> inline` function that uses any of the alternative structures you prefer,
> which would then permit this same macro for typing.
You'd need to have a different struct+function pair of wrappers for each
different type you need to allocate. My type-generic macro works for
all malloc(3) calls, so you only need to write it once.
Have a lovely night!
Alex
--
<https://www.alejandro-colomar.es>
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