Re: [patch libiberty include]: Add additional helper functions for directory-separator searching

[Kai Tietz <ktietz70@googlemail.com>]

2011/3/8 Eli Zaretskii <eliz@gnu.org>:
>> Date: Tue, 8 Mar 2011 11:56:45 +0100
>> From: Kai Tietz <ktietz70@googlemail.com>
>>
>> +@deftypefn Extension int filename_dirchr (const char *@var{p})
>> +
>> +The returned value is similar to what @code{strchr} would return for
>> +searching for a directory separator.
>> +
>> +This function does not normalize file name.  However, it does handle
>> +the fact that on DOS-like file systems, forward and backward slashes
>> +are directory separators.
>
> This is very mysterious.  The documentation should explain how this is
> "handled", or else the user will have no choice but to look in the
> sources.  And description "by similarity" doesn't help, because this
> function is obviously different from strchr in _some_ ways, but you
> don't say how.
>
> While at that, explain the problem this solves, or else the raison
> d'etre of this function will not be understood.  We do want this
> function to be used instead of just strchr, don't we?  For it to be
> used, its purpose and advantages should be well understood.
>
> Btw, why do we need filename_dirchr?  The use case for
> filename_dirrchr is clear, but in what situations will we need the
> other one?

As the comment notes. strchr/strrchr searches for one character. This
is for unix-file-system normally slash. On DOS based file-systems
there are two characters representing a directory-separator. Slash and
Backslash. Therefore this routine takes care that both are handled
similiar to a single character searching.

>> +  if (!r || (r2 && r2 < r))
>
> Why do you test for r2 being non-NULL?  You are not going to
> dereference it in the next comparison, and NULL is comparable as any
> other value.

As if we found slash, we don't want to override function's result by
backslash not found. If the null-check wouldn't be present condition
would be always true for r2 == NULL as, NULL is always less then a
pointer. But r shall be modified only if r2 (backslash) was found
before r (slash).
(same logic but here from right to left for the strrchr-case)

Regards,
Kai