Re: Can the new generic string functions accept void* arguments?

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From	Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups	comp.std.c
Subject	Re: Can the new generic string functions accept void* arguments?
Date	Fri, 02 Jun 2023 15:11:30 -0700
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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>> The latest draft of the upcoming C23 standard is:
>>     https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3096.pdf
>> It introduces several type-generic functions in <string.h>, replacing
>> normal functions of the same names: memchr, strchr, strpbrk, strrchr,
>> strstr.
>>
>> I'll use strchr() as an example; the same applies to the other str*()
>> generic functions (but not to memchr()).
> [...]
>
> Just after I posted the above, I thought of a potential issue with
> memchr() that just might affect real code.
[snip]

And I think I've found an even more serious issue with bsearch().

In C17 and earlier, bsearch() is declared as:

    void *bsearch(const void *key, const void *base,
         size_t nmemb, size_t size,
         int (*compar)(const void *, const void *));

`base` points to the object being searched.  The returned value is a
pointer to non-const void pointing to an element of the searched object.

C23 (as of N3096) has:

    QVoid *bsearch(const void *key, QVoid *base, size_t nmemb, size_t size,
          int (*compar)(const void *, const void *));

where QVoid is either void or const void, depending on the type of the
base argument.

The obvious implementation using _Generic will reject a base argument of
a type other than `void* or `const void*`.

(I see Ben posted a followup with a possible solution.  I haven't
studied it yet.)

I've been discussing this by email with the editors (listed on the first
page of N3096).

https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3096.pdf

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Will write code for food.
void Void(void) { Void(); } /* The recursive call of the void */

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Thread

Can the new generic string functions accept void* arguments? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-06-01 21:41 -0700
  Re: Can the new generic string functions accept void* arguments? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-06-01 22:18 -0700
    Re: Can the new generic string functions accept void* arguments? Jakob Bohm <jb-usenet@wisemo.com.invalid> - 2023-06-02 15:03 +0200
      Re: Can the new generic string functions accept void* arguments? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-06-02 11:52 -0700
    Re: Can the new generic string functions accept void* arguments? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-06-02 22:01 +0100
      Re: Can the new generic string functions accept void* arguments? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-06-04 21:37 -0700
        Re: Can the new generic string functions accept void* arguments? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-06-04 21:50 -0700
    Re: Can the new generic string functions accept void* arguments? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-06-02 15:11 -0700

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