From: Philipp Fent <fent@in.tum.de>
To: Jonathan Wakely <jwakely@redhat.com>
Cc: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
Subject: Re: [PATCH 2/2] libstdc++: Add pretty printer for std::stringstream
Date: Mon, 12 Sep 2022 10:37:10 +0200 [thread overview]
Message-ID: <de37a579-b844-9265-346c-5beb71b20728@in.tum.de> (raw)
In-Reply-To: <CACb0b4kDhRyRBJ1szfDN3Ot8Kewwh8CsXBO+=Pj1P-+H1tojPg@mail.gmail.com>
Hi Jonathan,
I've sent an updated patch addressing your comments here:
https://gcc.gnu.org/pipermail/libstdc++/2022-September/054587.html
Details below.
On 06.09.22 13:27, Jonathan Wakely wrote:
>> + pbase = self.val['_M_out_beg']
>> + pptr = self.val['_M_out_cur']
>> + egptr = self.val['_M_in_end']
>
> It would be nice to encapsulate this into a generic helper for all
> streambufs, as this part isn't specific to basic_stringbuf. We could
> then reuse it for printing spanbufs and other types in future. It
> could be a function that takes a streambuf and returns a tuple of
> (pbase, pptr, egptr).
I factored this into a reusable access_streambuf_ptrs().
>> + # Logic from basic_stringbuf::_M_high_mark()
>> + if pptr:
>> + if not egptr or pptr > egptr:
>> + return pbase.string(length = pptr - pbase)
>> + else:
>> + return pbase.string(length = pptr - egptr)
>
> Shouldn't this be egptr - pbase?
>
> This suggests the tests are inadequate. I think this bug would have
> been found by a test something like:
>
> std::stringstream ssin("input", std::ios::in);
> // { dg-final { note-test ssin "\"input\"" } }
>
> The (egptr - pbase) case is also needed for printing an istringstream.
Good catch! I fixed that bug and added a test for this in the testsuite.
>
>> + return self.val['_M_string']
>> +
>> + def display_hint(self):
>> + return 'string'
>> +
>> +class StdStringStreamPrinter:
>> + "Print a std::basic_stringstream"
>> +
>> + def __init__(self, _, val):
>> + self.val = val
>> +
>> + def to_string(self):
>> + return self.val['_M_stringbuf']
>
> This assumes that the stream is still using its stringbuf, which is
> probably true 99% of the time, but isn't guaranteed. In the following
> situation, the printer would give potentially misleading output:
>
> std::stringstream ss("xxx");
> ss.rdbuf(std::cin.rdbuf());
>
> I wonder if we want to have a check that self.val['_M_streambuf'] ==
> self.val['_M_stringbuf'].address
>
> Alternatively, don't provide a printer for the stringstream at all,
> just for the stringbuf, and then when GDB uses its default display for
> the stringstream it will show that member.
I didn't know one could redirect a stringstream, since its rdbuf()
method hides the basic_ios rdbuf() methods. But of course, that's still
possible via the base class...
The Patch v2 checks that case in the StdStringStreamPrinter constructor,
and follows that redirect in to_string().
>
>> +
>> + def display_hint(self):
>> + return 'string'
>> +
>> class Tr1HashtableIterator(Iterator):
>> def __init__ (self, hashtable):
>> self.buckets = hashtable['_M_buckets']
>> @@ -2232,6 +2265,10 @@ def build_libstdcxx_dictionary ():
>> libstdcxx_printer.add_version('std::', 'initializer_list',
>> StdInitializerListPrinter)
>> libstdcxx_printer.add_version('std::', 'atomic', StdAtomicPrinter)
>> + libstdcxx_printer.add_version('std::', 'basic_stringbuf', StdStringBufPrinter)
>> + libstdcxx_printer.add_version('std::__cxx11::', 'basic_stringbuf', StdStringBufPrinter)
>> + libstdcxx_printer.add_version('std::', 'basic_stringstream', StdStringStreamPrinter)
>> + libstdcxx_printer.add_version('std::__cxx11::', 'basic_stringstream', StdStringStreamPrinter)
>
> Wouldn't we want it for ostringstream and istringstream too?
Indeed. The updated patch registers the pretty printer for all flavors.
next prev parent reply other threads:[~2022-09-12 8:37 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-04 18:47 [PATCH 1/2] libstdc++: Fix pretty printer tests of tuple indexes Philipp Fent
2022-09-04 18:47 ` [PATCH 2/2] libstdc++: Add pretty printer for std::stringstream Philipp Fent
2022-09-06 11:27 ` Jonathan Wakely
2022-09-06 21:24 ` [PATCH v2] libstdc++: Add pretty printer for std::stringstreams Philipp Fent
2022-09-14 12:45 ` Jonathan Wakely
2022-09-12 8:37 ` Philipp Fent [this message]
2022-09-06 1:06 ` [PATCH 1/2] libstdc++: Fix pretty printer tests of tuple indexes Will Hawkins
2022-09-06 11:12 ` Jonathan Wakely
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