| From: | John Naylor <john(dot)naylor(at)enterprisedb(dot)com> |
|---|---|
| To: | Jelte Fennema <postgres(at)jeltef(dot)nl> |
| Cc: | Junwang Zhao <zhjwpku(at)gmail(dot)com>, Richard Guo <guofenglinux(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Should we use MemSet or {0} for struct initialization? |
| Date: | 2023-09-01 13:25:25 |
| Message-ID: | CAFBsxsEyj1nU96+_Gk0qHwt_Fe7ainRhKzX4ktU6PrnqM-EP2w@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Sep 1, 2023 at 7:48 PM Jelte Fennema <postgres(at)jeltef(dot)nl> wrote:
> The C standard says:
> > When a value is stored in an object of structure or union type,
including in a member object, the bytes of the object representation that
correspond to any padding bytes take unspecified values.
>
> So if you set any of the fields after a MemSet, the values of the
> padding bytes that were set to 0 are now unspecified. It seems much
> safer to actually spell out the padding fields of a hash key.
No, the standard is telling you why you need to memset if consistency of
padding bytes matters.
--
John Naylor
EDB: http://www.enterprisedb.com
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