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In addition to all the examples I gave in my answer to the linked post, all scenarios where p is a pointer to incomplete type fails. Not just the void* scenario, but also when p is a pointer to an ...
Answer
#1: Initial revision
by
Lundin
·
2022-02-14T14:58:33Z (almost 3 years ago)
In addition to all the examples I gave in my answer to the linked post, all scenarios where `p` is a pointer to incomplete type fails. Not just the `void*` scenario, but also when `p` is a pointer to an array of incomplete type:
int (*p)[] = malloc(n * sizeof *p); // will not compile cleanly
And also when using forward-declared structs/unions:
struct fwd_declared* p;
p = malloc(n * sizeof *p); // will not compile cleanly
And when using function pointers:
void (*p)(void);
p = malloc(n * sizeof *p); // will not compile cleanly
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All of these examples (including de-referencing `void` pointers) are invalid C as per C17 6.5.3.4:
> **Constraints**
>
> The `sizeof` operator shall not be applied to an expression that has function type or an incomplete type
Regarding "compile cleanly" please see [What must a C compiler do when it finds an error?](https://software.codidact.com/posts/277340)
And please note that gcc/clang are by default in a non-standard mode until you pass along `-std=c17 -pedantic-errors` to tell them to become conforming implementations.
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These are weak arguments against using a certain `malloc` style though.