Date: Tue, 12 Nov 2013 16:32:19 -0500 From: Eitan Adler <lists@eitanadler.com> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-current Current <freebsd-current@freebsd.org>, David Chisnall <theraven@freebsd.org>, Steve Kargl <sgk@troutmask.apl.washington.edu> Subject: Re: Are clang++ and libc++ compatible? Message-ID: <CAF6rxgn0YQT-PEKwNRds85EbXzh0S7uGCt918XzU5c9Fb8yzRA@mail.gmail.com> In-Reply-To: <201311121321.07330.jhb@freebsd.org> References: <20131112163219.GA2834@troutmask.apl.washington.edu> <20131112165422.GA2939@troutmask.apl.washington.edu> <CAF6rxgmRb3QALsSyVrpR683%2BVzcUnDN0VQja62xn8FTZaRxOKw@mail.gmail.com> <201311121321.07330.jhb@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Tue, Nov 12, 2013 at 1:21 PM, John Baldwin <jhb@freebsd.org> wrote:
> On Tuesday, November 12, 2013 1:11:04 pm Eitan Adler wrote:
>> On Tue, Nov 12, 2013 at 11:54 AM, Steve Kargl
>> <sgk@troutmask.apl.washington.edu> wrote:
>> > On Tue, Nov 12, 2013 at 04:38:17PM +0000, David Chisnall wrote:
>> >> On 12 Nov 2013, at 16:32, Steve Kargl <sgk@troutmask.apl.washington.edu>
> wrote:
>> >>
>> >>> Trying to build news/pan with clang++ dies with
>> >>>
>> >>> gmake[3]: Entering directory
> `/usr/ports/news/pan/work/pan-0.139/pan/general'
>> >>> CXX file-util.o
>> >>> In file included from file-util.cc:38:
>> >>> In file included from ./log.h:26:
>> >>> /usr/include/c++/v1/deque:907:49: error: invalid application of 'sizeof'
> to an
>> >>> incomplete type 'value_type' (aka 'pan::Log::Entry')
>> >>> static const difference_type __block_size = sizeof(value_type) < 256
> ? 4...
>> >>>
>> >>> Anyone know how to fix either clang++ or libc++?
>> >>
>> >> The error here does not appear to be in clang or libc++, but in the
>> >> use by the thing that you are compiling.
>> >> This is saying that you have tried to create a
> std::dequeu<pan::Log::Entry>,
>> >> but pan::Log::Entry is a forward declaration and so the template
>> >> instantiation fails.
>> >> The fix is to move the definition of pan::Log::Entry such that it
>> >> is visible at the time of its use.
>> >>
>> >
>> > I don't know C++, but it is at all like C, then the header files
>> > are normally placed at the top of a file before one's code. In
>> > this case, the code in news/pan/work/pan-0.139/pan/general/log.h
>> > looks like (where I've striped comment to keep it short)
>> >
>> > #ifndef __Log_h__
>> > #define __Log_h__
>> >
>> > #include <ctime>
>> > #include <set>
>> > #include <string>
>> > #include <deque>
>> >
>> > namespace pan
>> > {
>> > class Log
>> > {
>> > public:
>> > enum Severity {
>> > PAN_SEVERITY_INFO = 1,
>> > PAN_SEVERITY_ERROR = 2,
>> > PAN_SEVERITY_URGENT = (1<<10)
>> > };
>> >
>> > struct Entry {
>> > time_t date;
>> > Severity severity;
>> > std::deque<Entry> messages;
>> > std::string message;
>> > bool is_child;
>> > Entry() : is_child(false) { }
>> > };
>> >
>> > void add_entry(Entry& e, std::deque<Entry>& list);
>> >
>> >
>> > Are you saying that I need to move '#include <deque>' to
>> > the location above the 'void add_entry(...)' line?
>>
>> The problem here is that the code is trying to make a std::deque of
>> the type Entry before Entry is fully defined.
>> This is nearly identical to the problem in the simplified C code below:
>>
>> struct foo {
>> struct foo bar;
>> }
>
> Except it isn't. It's declaring the head of a container. This is more
> like:
>
> struct foo {
> TAILQ_HEAD(, foo) messages;
> };
>
> The problem is that unlike the queue macros (which are broken out into
> chunks), the compiler has to instantiate all of std::deque<> even though
> it will only use a portion of its definition. I understand why this is
> a limitation of C++, but it's not quite as brain damaged as your
> example.
Yes, I'm aware of this difference.
--
Eitan Adler
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAF6rxgn0YQT-PEKwNRds85EbXzh0S7uGCt918XzU5c9Fb8yzRA>