From: Jonathan Wakely <jwakely@redhat.com>
To: "Daniel Krügler" <daniel.kruegler@gmail.com>
Cc: libstdc++ <libstdc++@gcc.gnu.org>,
gcc-patches List <gcc-patches@gcc.gnu.org>
Subject: Re: [patch] Implement ISO/IEC TS 18822 C++ File system TS
Date: Fri, 01 May 2015 19:38:00 -0000 [thread overview]
Message-ID: <20150501193816.GJ3618@redhat.com> (raw)
In-Reply-To: <CAGNvRgCDMT3e6KA2oXL4BFZ2VLH3w=vRgRtK0+101=A0SA6eKQ@mail.gmail.com>
On 01/05/15 21:28 +0200, Daniel Krügler wrote:
>2015-05-01 20:22 GMT+02:00 Jonathan Wakely <jwakely@redhat.com>:
>> On 01/05/15 19:03 +0200, Daniel Krügler wrote:
>>>
>>> b/libstdc++-v3/src/filesystem/path.cc:
>>>
>>> - path::compare(const path& p) const noexcept:
>>>
>>> Shouldn't the implementation of this noexcept function not try to
>>> create copies of path objects? Couldn't _Cmpt just hold references to
>>> _M_pathname?
>>
>> All your other comments are definitely correct and I'll make the
>> relevant fixes soon, but I'm not sure what you mean here, could you
>> clarify?
>
>My remembrance of the difference in noexcept qualifications of
>
>int compare(const path& p) const noexcept;
>int compare(const string_type& s) const;
>int compare(const value_type* s) const;
>
>is that the latter are allowed to allocate memory to be implemented as
>the standard writes the corresponding functions for std::basic_string:
>
>int compare(const basic_string& str) const noexcept;
>int compare(const charT* s) const;
>
>Returns: compare(basic_string(s)).
>
>But if I read your implementation of path::compare(const path& p)
>correctly it *also* may allocate memory by copying _M_pathname into a
>_Cmpt object.
Yes, I agree that there's a bug here that could cause it to
std::terminate.
>I was wondering whether for this comparison there exists
>real need to *copy* _M_pathname (potentially exceeding the memory
>limits). Wouldn't it be possible to define a _CmptRef type that for
>the purpose of implementing compare(const path& p) just refers to
>references of the _M_pathname and therefore doesn't need to allocate
>any dynamic storage? (I should have spoken of a new type _CmptRef and
>not of your existing _Cmpt).
Ah, I see what you mean (I thought you were suggesting some
improvements to _Cmpt itself ... which might be possible so I'm glad
you made me think about it :-)
I think I wrote compare() like that because it was easier, and when I
first implemented this we had COW strings so it wouldn't throw when
copying. That isn't true now, so I need to change it.
next prev parent reply other threads:[~2015-05-01 19:38 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-30 17:42 Jonathan Wakely
2015-04-30 19:33 ` Jonathan Wakely
[not found] ` <CAFW6PZB9WvskzrKCsNKK4s-5oXWjcwkuZGMrWbrfgJ7fpJiCXQ@mail.gmail.com>
[not found] ` <20150501105351.GY3618@redhat.com>
2015-05-01 19:49 ` Jonathan Wakely
2015-05-02 9:52 ` Jonathan Wakely
2015-05-08 11:43 ` Rainer Orth
2015-05-13 10:56 ` Jonathan Wakely
2015-05-01 12:45 ` Rainer Orth
2015-05-01 15:11 ` Jonathan Wakely
2015-05-01 15:14 ` Rainer Orth
2015-05-01 17:03 ` Daniel Krügler
2015-05-01 17:55 ` Jonathan Wakely
2015-05-01 18:22 ` Jonathan Wakely
2015-05-01 19:28 ` Daniel Krügler
2015-05-01 19:38 ` Jonathan Wakely [this message]
2015-05-01 20:05 ` Jonathan Wakely
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