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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: "Why the C Language Will Never Stop You from Making Mistakes" by JeanHeyd Meneide
Date: Thu, 13 Aug 2020 00:41:04 -0700
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Scott Newman <scott69@gmail.com> writes:
>> Of course the initialization of p_dog is a constraint violation.  There
>> is no implicit conversion between incompatible pointer types (other than
>> the special case of void*).
>
> No, that's perfectl legal code.

I suppose that depends on what you mean by "legal" (the C standard
doesn't use that word to refer to code).  But it's definitely a
constraint violation.

Here's the full program:

#include <stdlib.h>

struct Meow {
 int a;
};

struct Bark {
 double b;
 void* c;
};

int main (int argc, char* argv[]) {
 (void)argc;
 (void)argv;

 struct Meow* p_cat = (struct Meow*)malloc(sizeof(struct Meow));
 struct Bark* p_dog = p_cat;
 // :3
 
 return 0;
}

struct Meo and struct Bark are not compatible types, so the
initialization violates the constraint in N1570 6.5.16.1p1,
referenced in 6.7.9p11.

(Either that, or I've misunderstood something and the authors of
gcc and clang made the same mistake.)

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips Healthcare
void Void(void) { Void(); } /* The recursive call of the void */