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Message-ID: <CAHktk4iYqdRPo01UpebvmmARPaTaDK0cvf8DOuThWv4uT4hp=A@mail.gmail.com>
Date: Fri, 27 Mar 2026 11:24:43 -0700
From: Charles Munger <clm@...gle.com>
To: Alejandro Colomar <une+c@...jandro-colomar.es>
Cc: sc22wg14@...n-std.org, Rich Felker <dalias@...c.org>, musl@...ts.openwall.com
Subject: Re: [SC22WG14.36006] N3849 - Memory allocation with size feedback v2,
request for feedback
If you prefer that macro, you can keep it like so:
https://godbolt.org/z/rb6s4j864
I was able to get the struct version of your macro working in clang, but
not gcc. But I think what's important is that if you like that style of API
and you are already defining a wrapper macro, you can get it at no overhead
with a static inline function; but I believe the struct is preferable as an
API to standardize for the reasons described in the doc.
On Mon, Mar 23, 2026 at 6:26 PM Alejandro Colomar <
une+c@...jandro-colomar.es> wrote:
> 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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