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Re: c++/3795: The "bitset" template from the STL doesn't work properly
- To: gcc-bugs at gcc dot gnu dot org, gcc-prs at gcc dot gnu dot org, martin dot rieger at mmr2 dot sianum dot de, nobody at gcc dot gnu dot org, pme at gcc dot gnu dot org
- Subject: Re: c++/3795: The "bitset" template from the STL doesn't work properly
- From: pme at gcc dot gnu dot org
- Date: 24 Jul 2001 19:05:33 -0000
Synopsis: The "bitset" template from the STL doesn't work properly
Responsible-Changed-From-To: unassigned->pme
Responsible-Changed-By: pme
Responsible-Changed-When: Tue Jul 24 12:05:33 2001
Responsible-Changed-Why:
Priority changed to low because there is a workaround.
State-Changed-From-To: open->analyzed
State-Changed-By: pme
State-Changed-When: Tue Jul 24 12:05:33 2001
State-Changed-Why:
Thank you for your bug report.
As far as (1) goes, this is not a bug. In fact,
this has already been reported to the ISO C++
committee with the note, "...the user cannot
pass this template constructor a const char* and
expect a conversion to basic_string. The reason
is "When you have a template constructor, it can
get used in contexts where type deduction can
be done. Type deduction basically comes up with
exact matches, not ones involving conversions.""
The LWG's response is, "Although the problem
is real, the standard is designed that way
so it is not a defect. Education is the
immediate workaround. A future standard may
wish to consider the Proposed Resolution as
an extension." The proposed resolution was to
add another constructor taking a const char*.
Okay, problem (2)... yeah, that does seem kinda
stupid, but I can understand the reasoning.
(This may not even be a defect in the standard,
in which case one of the people on the LWG can
close this PR.) The tricky part is that string
is a templated type, and bitset<> doesn't know
what parameters to use when instantiating the
string returned from to_string(). You need
to write
bs.to_string<char,char_traits<char>,allocator<char> >()
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
to instantiate the member template function.
Although I would argue that the signature
preceeding [23.3.5.2]/33 should allow the second
and third template arguments to have default
values, like basic_string<char> does, so that
bs.to_string<char>()
could work.
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view&pr=3795&database=gcc