Bugs
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## Bugs

### Implementation Bugs

Information on known bugs, details on efforts to fix them, and fixed bugs are all available as part of the GCC bug tracking system, with the category set to `libstdc++`.

### Standard Bugs

Everybody's got issues. Even the C++ Standard Library.

The Library Working Group, or LWG, is the ISO subcommittee responsible for making changes to the library. They periodically publish an Issues List containing problems and possible solutions. As they reach a consensus on proposed solutions, we often incorporate the solution.

Here are the issues which have resulted in code changes to the library. The links are to the specific defect reports from a partial copy of the Issues List. You can read the full version online at the ISO C++ Committee homepage, linked to on the GCC "Readings" page. If you spend a lot of time reading the issues, we recommend downloading the ZIP file and reading them locally.

(NB: partial copy means that not all links within the lwg-*.html pages will work. Specifically, links to defect reports that have not been accorded full DR status will probably break. Rather than trying to mirror the entire issues list on our overworked web server, we recommend you go to the LWG homepage instead.)

If a DR is not listed here, we may simply not have gotten to it yet; feel free to submit a patch. Search the include/bits and src directories for appearances of `_GLIBCXX_RESOLVE_LIB_DEFECTS` for examples of style. Note that we usually do not make changes to the code until an issue has reached DR status.

5: string::compare specification questionable

  This should be two overloaded functions rather than a single function.

17: Bad bool parsing

  Apparently extracting Boolean values was messed up...

19: "Noconv" definition too vague

  If `codecvt::do_in` returns `noconv` there are no changes to the values in `[to, to_limit)`.

22: Member open vs flags

  Re-opening a file stream does not clear the state flags.

23: Num_get overflow result

  Implement the proposed resolution.

25: String operator<< uses width() value wrong

  Padding issues.

48: Use of non-existent exception constructor

  An instance of `ios_base::failure` is constructed instead.

49: Underspecification of ios_base::sync_with_stdio

  The return type is the previous state of synchronization.

50: Copy constructor and assignment operator of ios_base

  These members functions are declared `private` and are thus inaccessible. Specifying the correct semantics of "copying stream state" was deemed too complicated.

60: What is a formatted input function?

  This DR made many widespread changes to `basic_istream` and `basic_ostream` all of which have been implemented.

63: Exception-handling policy for unformatted output

  Make the policy consistent with that of formatted input, unformatted input, and formatted output.

68: Extractors for char* should store null at end

  And they do now. An editing glitch in the last item in the list of [27.6.1.2.3]/7.

74: Garbled text for codecvt::do_max_length

  The text of the standard was gibberish. Typos gone rampant.

75: Contradiction in codecvt::length's argument types

  Change the first parameter to `stateT&` and implement the new effects paragraph.

83: string::npos vs. string::max_size()

  Safety checks on the size of the string should test against `max_size()` rather than `npos`.

90: Incorrect description of operator>> for strings

  The effect contain `isspace(c,getloc())` which must be replaced by `isspace(c,is.getloc())`.

91: Description of operator>> and getline() for string<> might cause endless loop

  They behave as a formatted input function and as an unformatted input function, respectively (except that `getline` is not required to set `gcount`).

103: set::iterator is required to be modifiable, but this allows modification of keys.

  For associative containers where the value type is the same as the key type, both `iterator` and `const_iterator` are constant iterators.

109: Missing binders for non-const sequence elements

  The `binder1st` and `binder2nd` didn't have an `operator()` taking a non-const parameter.

110: istreambuf_iterator::equal not const

  This was not a const member function. Note that the DR says to replace the function with a const one; we have instead provided an overloaded version with identical contents.

117: basic_ostream uses nonexistent num_put member functions

  `num_put::put()` was overloaded on the wrong types.

118: basic_istream uses nonexistent num_get member functions

  Same as 117, but for `num_get::get()`.

129: Need error indication from seekp() and seekg()

  These functions set `failbit` on error now.

130: Return type of container::erase(iterator) differs for associative containers

  Make member `erase` return iterator for `set`, `multiset`, `map`, `multimap`.

136: seekp, seekg setting wrong streams?

  `seekp` should only set the output stream, and `seekg` should only set the input stream.

167: Improper use of traits_type::length()

  `op<<` with a `const char*` was calculating an incorrect number of characters to write.

169: Bad efficiency of overflow() mandated

  Grow efficiently the internal array object.

171: Strange seekpos() semantics due to joint position

  Quite complex to summarize...

181: make_pair() unintended behavior

  This function used to take its arguments as reference-to-const, now it copies them (pass by value).

195: Should basic_istream::sentry's constructor ever set eofbit?

  Yes, it can, specifically if EOF is reached while skipping whitespace.

211: operator>>(istream&, string&) doesn't set failbit

  If nothing is extracted into the string, `op>>` now sets `failbit` (which can cause an exception, etc., etc.).

214: set::find() missing const overload

  Both `set` and `multiset` were missing overloaded find, lower_bound, upper_bound, and equal_range functions for const instances.

231: Precision in iostream?

  For conversion from a floating-point type, `str.precision()` is specified in the conversion specification.

233: Insertion hints in associative containers

  Implement N1780, first check before then check after, insert as close to hint as possible.

235: No specification of default ctor for reverse_iterator

  The declaration of `reverse_iterator` lists a default constructor. However, no specification is given what this constructor should do.

241: Does unique_copy() require CopyConstructible and Assignable?

  Add a helper for forward_iterator/output_iterator, fix the existing one for input_iterator/output_iterator to not rely on Assignability.

243: get and getline when sentry reports failure

  Store a null character only if the character array has a non-zero size.

251: basic_stringbuf missing allocator_type

  This nested typedef was originally not specified.

253: valarray helper functions are almost entirely useless

  Make the copy constructor and copy-assignment operator declarations public in gslice_array, indirect_array, mask_array, slice_array; provide definitions.

265: std::pair::pair() effects overly restrictive

  The default ctor would build its members from copies of temporaries; now it simply uses their respective default ctors.

266: bad_exception::~bad_exception() missing Effects clause

  The `bad_`* classes no longer have destructors (they are trivial), since no description of them was ever given.

271: basic_iostream missing typedefs

  The typedefs it inherits from its base classes can't be used, since (for example) `basic_iostream<T>::traits_type` is ambiguous.

275: Wrong type in num_get::get() overloads

  Similar to 118.

280: Comparison of reverse_iterator to const reverse_iterator

  Add global functions with two template parameters. (NB: not added for now a templated assignment operator)

292: Effects of a.copyfmt (a)

  If `(this == &rhs)` do nothing.

300: List::merge() specification incomplete

  If `(this == &x)` do nothing.

303: Bitset input operator underspecified

  Basically, compare the input character to `is.widen(0)` and `is.widen(1)`.

305: Default behavior of codecvt<wchar_t, char, mbstate_t>::length()

  Do not specify what `codecvt<wchar_t, char, mbstate_t>::do_length` must return.

328: Bad sprintf format modifier in money_put<>::do_put()

  Change the format string to "%.0Lf".

365: Lack of const-qualification in clause 27

  Add const overloads of `is_open`.

387: std::complex over-encapsulated

  Add the `real(T)` and `imag(T)` members; in C++11 mode, also adjust the existing `real()` and `imag()` members and free functions.

389: Const overload of valarray::operator[] returns by value

  Change it to return a `const T&`.

396: what are characters zero and one

  Implement the proposed resolution.

402: Wrong new expression in [some_]allocator::construct

  Replace "new" with "::new".

408: Is vector<reverse_iterator<char*> > forbidden?

  Tweak the debug-mode checks in _Safe_iterator.

409: Closing an fstream should clear the error state

  Have `open` clear the error flags.

431: Swapping containers with unequal allocators

  Implement Option 3, as per N1599.

432: stringbuf::overflow() makes only one write position available

  Implement the resolution, beyond DR 169.

434: bitset::to_string() hard to use

  Add three overloads, taking fewer template arguments.

438: Ambiguity in the "do the right thing" clause

  Implement the resolution, basically cast less.

453: basic_stringbuf::seekoff need not always fail for an empty stream

  Don't fail if the next pointer is null and newoff is zero.

455: cerr::tie() and wcerr::tie() are overspecified

  Initialize cerr tied to cout and wcerr tied to wcout.

464: Suggestion for new member functions in standard containers

  Add `data()` to `std::vector` and `at(const key_type&)` to `std::map`.

508: Bad parameters for ranlux64_base_01

  Fix the parameters.

512: Seeding subtract_with_carry_01 from a single unsigned long

  Construct a `linear_congruential` engine and seed with it.

526: Is it undefined if a function in the standard changes in parameters?

  Use &value.

538: 241 again: Does unique_copy() require CopyConstructible and Assignable?

  In case of input_iterator/output_iterator rely on Assignability of input_iterator' value_type.

539: partial_sum and adjacent_difference should mention requirements

  We were almost doing the right thing, just use std::move in adjacent_difference.

541: shared_ptr template assignment and void

  Add an auto_ptr<void> specialization.

543: valarray slice default constructor

  Follow the straightforward proposed resolution.

550: What should the return type of pow(float,int) be?

  In C++11 mode, remove the pow(float,int), etc., signatures.

586: string inserter not a formatted function

  Change it to be a formatted output function (i.e. catch exceptions).

596: 27.8.1.3 Table 112 omits "a+" and "a+b" modes

  Add the missing modes to fopen_mode.

630: arrays of valarray

  Implement the simple resolution.

660: Missing bitwise operations

  Add the missing operations.

691: const_local_iterator cbegin, cend missing from TR1

  In C++11 mode add cbegin(size_type) and cend(size_type) to the unordered containers.

693: std::bitset::all() missing

  Add it, consistently with the discussion.

695: ctype<char>::classic_table() not accessible

  Make the member functions table and classic_table public.

696: istream::operator>>(int&) broken

  Implement the straightforward resolution.

761: unordered_map needs an at() member function

  In C++11 mode, add at() and at() const.

775: Tuple indexing should be unsigned?

  Implement the int -> size_t replacements.

776: Undescribed assign function of std::array

  In C++11 mode, remove assign, add fill.

781: std::complex should add missing C99 functions

  In C++11 mode, add std::proj.

809: std::swap should be overloaded for array types

  Add the overload.

844: complex pow return type is ambiguous

  In C++11 mode, remove the pow(complex<T>, int) signature.

853: to_string needs updating with zero and one

  Update / add the signatures.

865: More algorithms that throw away information

  The traditional HP / SGI return type and value is blessed by the resolution of the DR.

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