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Date: Tue, 11 Aug 2015 22:31:11 +0000
From: Daniel Shahaf <d.s@daniel.shahaf.name>
To: dev@subversion.apache.org
Subject: Re: Review of sizeof usage
Message-ID: <20150811223111.GH1859@tarsus.local2>
References: 
 <CA+t0gk0QV_2mwEmK-OPjoP9BzXCPPiKccW3Wg3tBwPmQcLUgcQ@mail.gmail.com>
 <87pp2tvpfc.fsf@wandisco.com>
 <55CA5344.8090005@wandisco.com>
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In-Reply-To: <55CA5344.8090005@wandisco.com>
User-Agent: Mutt/1.5.21 (2010-09-15)

Branko Čibej wrote on Tue, Aug 11, 2015 at 21:55:48 +0200:
> On 11.08.2015 17:02, Philip Martin wrote:
> > Stefan Fuhrmann <stefan.fuhrmann@wandisco.com> writes:
> >
> >> way we use sizeof. In my opinion, we should take the
> >> size of the created or processed variable instead of its
> >> type, i.e.
> >>
> >>   abc_t *v = apr_pcalloc(pool, sizeof(*v));
> >>   apr_hash_set(hash, key, sizeof(*key), y);
> >>   z = apr_hash_get(hash, key, sizeof(*key));
> >>
> >> rather than
> >>
> >>   abc_t *v = apr_pcalloc(pool, sizeof(abc_t));
> >>   apr_hash_set(hash, key, sizeof(key_t), y);
> >>   z = apr_hash_get(hash, key, sizeof(key_t));

Both of these variants are redundant.  We could encapsulate the
redundancy in a macro:

    #define SVN__CALLOC(obj, pool) do { (obj) = apr_pcalloc((pool), sizeof(*(obj))); } while (0)
    {
      abc_t *v;
      SVN__CALLOC(v, pool);
    }

> > We have had problems with both styles in the past, so neither is immune
> > to bugs.  I prefer the explicit type as it is easier to grep.
> 
> The explicit type form is more accident-prone than the variable form
> because any change requires two modifications in the same statement
> instead of one.

Why doesn't the compiler or buildbot catch accidents?