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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: sizeof object got by dereferencing uniniitalized pointer
Date: Thu, 28 Nov 2019 17:47:24 -0800
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Ben Bacarisse <ben.usenet@bsb.me.uk> writes:

> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>
>> Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
>>
>>> Thiago Adams <thiago.adams@gmail.com> writes:
>>> <cut>
>>>
>>>> Only when applied to variably types, sizeof is in runtime.
>>>>
>>>>   int n = 10;
>>>>
>>>>   int(*buf)[n] = malloc(sizeof(int) * n);
>>>
>>> Why would you not write
>>>
>>>    int (*buf)[n] = malloc(sizof *buf);
>>>
>>> ?
>>
>> Perhaps because, technically speaking, the right-hand side here
>> has undefined behavior?
>
> Yes, it has.  That has always puzzled me.  Do you think that this usage
> was specifically being ruled out, or is it a casualty of having made an
> overly simple decision[1]?

Short answer:  overly simple decision casualty.  But that is just
a guess, if I have time I will try to give a more thoughtful
answer later.