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 12:25:37 +0100
>> From: Kai Tietz <ktietz70@googlemail.com>
>> Cc: binutils@sourceware.org, gdb-patches@sourceware.org,
>>       gcc-patches@gcc.gnu.org
>>
>> > 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.
>
> We are miscommunicating.  I was asking when would a program want to
> find the _first_ directory separator character in a file name.
> Searching for the last one is a frequent use case: when you want to
> create a file in the same directory as another, or when you are
> looking for a basename of a file.  But when do you need the first
> slash?

See for example remote-fileio.c in remote_fileio_extract_ptr_w_len()
as an example. There is more then one use-case.

>> >> +  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)
>
> But in strrchr-case, r2 cannot be greater than r1 if it is NULL,
> right?
It can. It is a matter of signness of pointer comparision.

Regards,
Kai