basic_string.h

Go to the documentation of this file.

// Components for manipulating sequences of characters -*- C++ -*-

// Copyright (C) 1997-2013 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file bits/basic_string.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{string}
 */

//
// ISO C++ 14882: 21 Strings library
//

#ifndef _BASIC_STRING_H
#define _BASIC_STRING_H 1

#pragma GCC system_header

#include <ext/atomicity.h>
#include <debug/debug.h>
#if __cplusplus >= 201103L
#include <initializer_list>
#endif

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  /**
   *  @class basic_string basic_string.h <string>
   *  @brief  Managing sequences of characters and character-like objects.
   *
   *  @ingroup strings
   *  @ingroup sequences
   *
   *  @tparam _CharT  Type of character
   *  @tparam _Traits  Traits for character type, defaults to
   *                   char_traits<_CharT>.
   *  @tparam _Alloc  Allocator type, defaults to allocator<_CharT>.
   *
   *  Meets the requirements of a <a href="tables.html#65">container</a>, a
   *  <a href="tables.html#66">reversible container</a>, and a
   *  <a href="tables.html#67">sequence</a>.  Of the
   *  <a href="tables.html#68">optional sequence requirements</a>, only
   *  @c push_back, @c at, and @c %array access are supported.
   *
   *  @doctodo
   *
   *
   *  Documentation?  What's that?
   *  Nathan Myers <[email protected]>.
   *
   *  A string looks like this:
   *
   *  @code
   *                                        [_Rep]
   *                                        _M_length
   *   [basic_string<char_type>]            _M_capacity
   *   _M_dataplus                          _M_refcount
   *   _M_p ---------------->               unnamed array of char_type
   *  @endcode
   *
   *  Where the _M_p points to the first character in the string, and
   *  you cast it to a pointer-to-_Rep and subtract 1 to get a
   *  pointer to the header.
   *
   *  This approach has the enormous advantage that a string object
   *  requires only one allocation.  All the ugliness is confined
   *  within a single %pair of inline functions, which each compile to
   *  a single @a add instruction: _Rep::_M_data(), and
   *  string::_M_rep(); and the allocation function which gets a
   *  block of raw bytes and with room enough and constructs a _Rep
   *  object at the front.
   *
   *  The reason you want _M_data pointing to the character %array and
   *  not the _Rep is so that the debugger can see the string
   *  contents. (Probably we should add a non-inline member to get
   *  the _Rep for the debugger to use, so users can check the actual
   *  string length.)
   *
   *  Note that the _Rep object is a POD so that you can have a
   *  static <em>empty string</em> _Rep object already @a constructed before
   *  static constructors have run.  The reference-count encoding is
   *  chosen so that a 0 indicates one reference, so you never try to
   *  destroy the empty-string _Rep object.
   *
   *  All but the last paragraph is considered pretty conventional
   *  for a C++ string implementation.
  */
  // 21.3  Template class basic_string
  template<typename _CharT, typename _Traits, typename _Alloc>
    class basic_string
    {
      typedef typename _Alloc::template rebind<_CharT>::other _CharT_alloc_type;

      // Types:
    public:
      typedef _Traits                       traits_type;
      typedef typename _Traits::char_type           value_type;
      typedef _Alloc                        allocator_type;
      typedef typename _CharT_alloc_type::size_type     size_type;
      typedef typename _CharT_alloc_type::difference_type   difference_type;
      typedef typename _CharT_alloc_type::reference     reference;
      typedef typename _CharT_alloc_type::const_reference   const_reference;
      typedef typename _CharT_alloc_type::pointer       pointer;
      typedef typename _CharT_alloc_type::const_pointer     const_pointer;
      typedef __gnu_cxx::__normal_iterator<pointer, basic_string>  iterator;
      typedef __gnu_cxx::__normal_iterator<const_pointer, basic_string>
                                                            const_iterator;
      typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
      typedef std::reverse_iterator<iterator>           reverse_iterator;

    private:
      // _Rep: string representation
      //   Invariants:
      //   1. String really contains _M_length + 1 characters: due to 21.3.4
      //      must be kept null-terminated.
      //   2. _M_capacity >= _M_length
      //      Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).
      //   3. _M_refcount has three states:
      //      -1: leaked, one reference, no ref-copies allowed, non-const.
      //       0: one reference, non-const.
      //     n>0: n + 1 references, operations require a lock, const.
      //   4. All fields==0 is an empty string, given the extra storage
      //      beyond-the-end for a null terminator; thus, the shared
      //      empty string representation needs no constructor.

      struct _Rep_base
      {
    size_type       _M_length;
    size_type       _M_capacity;
    _Atomic_word        _M_refcount;
      };

      struct _Rep : _Rep_base
      {
    // Types:
    typedef typename _Alloc::template rebind<char>::other _Raw_bytes_alloc;

    // (Public) Data members:

    // The maximum number of individual char_type elements of an
    // individual string is determined by _S_max_size. This is the
    // value that will be returned by max_size().  (Whereas npos
    // is the maximum number of bytes the allocator can allocate.)
    // If one was to divvy up the theoretical largest size string,
    // with a terminating character and m _CharT elements, it'd
    // look like this:
    // npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
    // Solving for m:
    // m = ((npos - sizeof(_Rep))/sizeof(CharT)) - 1
    // In addition, this implementation quarters this amount.
    static const size_type  _S_max_size;
    static const _CharT _S_terminal;

    // The following storage is init'd to 0 by the linker, resulting
        // (carefully) in an empty string with one reference.
        static size_type _S_empty_rep_storage[];

        static _Rep&
        _S_empty_rep()
        { 
      // NB: Mild hack to avoid strict-aliasing warnings.  Note that
      // _S_empty_rep_storage is never modified and the punning should
      // be reasonably safe in this case.
      void* __p = reinterpret_cast<void*>(&_S_empty_rep_storage);
      return *reinterpret_cast<_Rep*>(__p);
    }

        bool
    _M_is_leaked() const
        { return this->_M_refcount < 0; }

        bool
    _M_is_shared() const
        { return this->_M_refcount > 0; }

        void
    _M_set_leaked()
        { this->_M_refcount = -1; }

        void
    _M_set_sharable()
        { this->_M_refcount = 0; }

    void
    _M_set_length_and_sharable(size_type __n)
    {
#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0
      if (__builtin_expect(this != &_S_empty_rep(), false))
#endif
        {
          this->_M_set_sharable();  // One reference.
          this->_M_length = __n;
          traits_type::assign(this->_M_refdata()[__n], _S_terminal);
          // grrr. (per 21.3.4)
          // You cannot leave those LWG people alone for a second.
        }
    }

    _CharT*
    _M_refdata() throw()
    { return reinterpret_cast<_CharT*>(this + 1); }

    _CharT*
    _M_grab(const _Alloc& __alloc1, const _Alloc& __alloc2)
    {
      return (!_M_is_leaked() && __alloc1 == __alloc2)
              ? _M_refcopy() : _M_clone(__alloc1);
    }

    // Create & Destroy
    static _Rep*
    _S_create(size_type, size_type, const _Alloc&);

    void
    _M_dispose(const _Alloc& __a)
    {
#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0
      if (__builtin_expect(this != &_S_empty_rep(), false))
#endif
        {
          // Be race-detector-friendly.  For more info see bits/c++config.
          _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&this->_M_refcount);
          if (__gnu_cxx::__exchange_and_add_dispatch(&this->_M_refcount,
                             -1) <= 0)
        {
          _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&this->_M_refcount);
          _M_destroy(__a);
        }
        }
    }  // XXX MT

    void
    _M_destroy(const _Alloc&) throw();

    _CharT*
    _M_refcopy() throw()
    {
#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0
      if (__builtin_expect(this != &_S_empty_rep(), false))
#endif
            __gnu_cxx::__atomic_add_dispatch(&this->_M_refcount, 1);
      return _M_refdata();
    }  // XXX MT

    _CharT*
    _M_clone(const _Alloc&, size_type __res = 0);
      };

      // Use empty-base optimization: http://www.cantrip.org/emptyopt.html
      struct _Alloc_hider : _Alloc
      {
    _Alloc_hider(_CharT* __dat, const _Alloc& __a)
    : _Alloc(__a), _M_p(__dat) { }

    _CharT* _M_p; // The actual data.
      };

    public:
      // Data Members (public):
      // NB: This is an unsigned type, and thus represents the maximum
      // size that the allocator can hold.
      ///  Value returned by various member functions when they fail.
      static const size_type    npos = static_cast<size_type>(-1);

    private:
      // Data Members (private):
      mutable _Alloc_hider  _M_dataplus;

      _CharT*
      _M_data() const
      { return  _M_dataplus._M_p; }

      _CharT*
      _M_data(_CharT* __p)
      { return (_M_dataplus._M_p = __p); }

      _Rep*
      _M_rep() const
      { return &((reinterpret_cast<_Rep*> (_M_data()))[-1]); }

      // For the internal use we have functions similar to `begin'/`end'
      // but they do not call _M_leak.
      iterator
      _M_ibegin() const
      { return iterator(_M_data()); }

      iterator
      _M_iend() const
      { return iterator(_M_data() + this->size()); }

      void
      _M_leak()    // for use in begin() & non-const op[]
      {
    if (!_M_rep()->_M_is_leaked())
      _M_leak_hard();
      }

      size_type
      _M_check(size_type __pos, const char* __s) const
      {
    if (__pos > this->size())
      __throw_out_of_range(__N(__s));
    return __pos;
      }

      void
      _M_check_length(size_type __n1, size_type __n2, const char* __s) const
      {
    if (this->max_size() - (this->size() - __n1) < __n2)
      __throw_length_error(__N(__s));
      }

      // NB: _M_limit doesn't check for a bad __pos value.
      size_type
      _M_limit(size_type __pos, size_type __off) const
      {
    const bool __testoff =  __off < this->size() - __pos;
    return __testoff ? __off : this->size() - __pos;
      }

      // True if _Rep and source do not overlap.
      bool
      _M_disjunct(const _CharT* __s) const
      {
    return (less<const _CharT*>()(__s, _M_data())
        || less<const _CharT*>()(_M_data() + this->size(), __s));
      }

      // When __n = 1 way faster than the general multichar
      // traits_type::copy/move/assign.
      static void
      _M_copy(_CharT* __d, const _CharT* __s, size_type __n)
      {
    if (__n == 1)
      traits_type::assign(*__d, *__s);
    else
      traits_type::copy(__d, __s, __n);
      }

      static void
      _M_move(_CharT* __d, const _CharT* __s, size_type __n)
      {
    if (__n == 1)
      traits_type::assign(*__d, *__s);
    else
      traits_type::move(__d, __s, __n);   
      }

      static void
      _M_assign(_CharT* __d, size_type __n, _CharT __c)
      {
    if (__n == 1)
      traits_type::assign(*__d, __c);
    else
      traits_type::assign(__d, __n, __c);     
      }

      // _S_copy_chars is a separate template to permit specialization
      // to optimize for the common case of pointers as iterators.
      template<class _Iterator>
        static void
        _S_copy_chars(_CharT* __p, _Iterator __k1, _Iterator __k2)
        {
      for (; __k1 != __k2; ++__k1, ++__p)
        traits_type::assign(*__p, *__k1); // These types are off.
    }

      static void
      _S_copy_chars(_CharT* __p, iterator __k1, iterator __k2)
      { _S_copy_chars(__p, __k1.base(), __k2.base()); }

      static void
      _S_copy_chars(_CharT* __p, const_iterator __k1, const_iterator __k2)
      { _S_copy_chars(__p, __k1.base(), __k2.base()); }

      static void
      _S_copy_chars(_CharT* __p, _CharT* __k1, _CharT* __k2)
      { _M_copy(__p, __k1, __k2 - __k1); }

      static void
      _S_copy_chars(_CharT* __p, const _CharT* __k1, const _CharT* __k2)
      { _M_copy(__p, __k1, __k2 - __k1); }

      static int
      _S_compare(size_type __n1, size_type __n2)
      {
    const difference_type __d = difference_type(__n1 - __n2);

    if (__d > __gnu_cxx::__numeric_traits<int>::__max)
      return __gnu_cxx::__numeric_traits<int>::__max;
    else if (__d < __gnu_cxx::__numeric_traits<int>::__min)
      return __gnu_cxx::__numeric_traits<int>::__min;
    else
      return int(__d);
      }

      void
      _M_mutate(size_type __pos, size_type __len1, size_type __len2);

      void
      _M_leak_hard();

      static _Rep&
      _S_empty_rep()
      { return _Rep::_S_empty_rep(); }

    public:
      // Construct/copy/destroy:
      // NB: We overload ctors in some cases instead of using default
      // arguments, per 17.4.4.4 para. 2 item 2.

      /**
       *  @brief  Default constructor creates an empty string.
       */
      basic_string()
#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0
      : _M_dataplus(_S_empty_rep()._M_refdata(), _Alloc()) { }
#else
      : _M_dataplus(_S_construct(size_type(), _CharT(), _Alloc()), _Alloc()){ }
#endif

      /**
       *  @brief  Construct an empty string using allocator @a a.
       */
      explicit
      basic_string(const _Alloc& __a);

      // NB: per LWG issue 42, semantics different from IS:
      /**
       *  @brief  Construct string with copy of value of @a str.
       *  @param  __str  Source string.
       */
      basic_string(const basic_string& __str);
      /**
       *  @brief  Construct string as copy of a substring.
       *  @param  __str  Source string.
       *  @param  __pos  Index of first character to copy from.
       *  @param  __n  Number of characters to copy (default remainder).
       */
      basic_string(const basic_string& __str, size_type __pos,
           size_type __n = npos);
      /**
       *  @brief  Construct string as copy of a substring.
       *  @param  __str  Source string.
       *  @param  __pos  Index of first character to copy from.
       *  @param  __n  Number of characters to copy.
       *  @param  __a  Allocator to use.
       */
      basic_string(const basic_string& __str, size_type __pos,
           size_type __n, const _Alloc& __a);

      /**
       *  @brief  Construct string initialized by a character %array.
       *  @param  __s  Source character %array.
       *  @param  __n  Number of characters to copy.
       *  @param  __a  Allocator to use (default is default allocator).
       *
       *  NB: @a __s must have at least @a __n characters, &apos;\\0&apos;
       *  has no special meaning.
       */
      basic_string(const _CharT* __s, size_type __n,
           const _Alloc& __a = _Alloc());
      /**
       *  @brief  Construct string as copy of a C string.
       *  @param  __s  Source C string.
       *  @param  __a  Allocator to use (default is default allocator).
       */
      basic_string(const _CharT* __s, const _Alloc& __a = _Alloc());
      /**
       *  @brief  Construct string as multiple characters.
       *  @param  __n  Number of characters.
       *  @param  __c  Character to use.
       *  @param  __a  Allocator to use (default is default allocator).
       */
      basic_string(size_type __n, _CharT __c, const _Alloc& __a = _Alloc());

#if __cplusplus >= 201103L
      /**
       *  @brief  Move construct string.
       *  @param  __str  Source string.
       *
       *  The newly-created string contains the exact contents of @a __str.
       *  @a __str is a valid, but unspecified string.
       **/
      basic_string(basic_string&& __str) noexcept
      : _M_dataplus(__str._M_dataplus)
      {
#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0
    __str._M_data(_S_empty_rep()._M_refdata());
#else
    __str._M_data(_S_construct(size_type(), _CharT(), get_allocator()));
#endif
      }

      /**
       *  @brief  Construct string from an initializer %list.
       *  @param  __l  std::initializer_list of characters.
       *  @param  __a  Allocator to use (default is default allocator).
       */
      basic_string(initializer_list<_CharT> __l, const _Alloc& __a = _Alloc());
#endif // C++11

      /**
       *  @brief  Construct string as copy of a range.
       *  @param  __beg  Start of range.
       *  @param  __end  End of range.
       *  @param  __a  Allocator to use (default is default allocator).
       */
      template<class _InputIterator>
        basic_string(_InputIterator __beg, _InputIterator __end,
             const _Alloc& __a = _Alloc());

      /**
       *  @brief  Destroy the string instance.
       */
      ~basic_string() _GLIBCXX_NOEXCEPT
      { _M_rep()->_M_dispose(this->get_allocator()); }

      /**
       *  @brief  Assign the value of @a str to this string.
       *  @param  __str  Source string.
       */
      basic_string&
      operator=(const basic_string& __str) 
      { return this->assign(__str); }

      /**
       *  @brief  Copy contents of @a s into this string.
       *  @param  __s  Source null-terminated string.
       */
      basic_string&
      operator=(const _CharT* __s) 
      { return this->assign(__s); }

      /**
       *  @brief  Set value to string of length 1.
       *  @param  __c  Source character.
       *
       *  Assigning to a character makes this string length 1 and
       *  (*this)[0] == @a c.
       */
      basic_string&
      operator=(_CharT __c) 
      { 
    this->assign(1, __c); 
    return *this;
      }

#if __cplusplus >= 201103L
      /**
       *  @brief  Move assign the value of @a str to this string.
       *  @param  __str  Source string.
       *
       *  The contents of @a str are moved into this string (without copying).
       *  @a str is a valid, but unspecified string.
       **/
      basic_string&
      operator=(basic_string&& __str)
      {
    // NB: DR 1204.
    this->swap(__str);
    return *this;
      }

      /**
       *  @brief  Set value to string constructed from initializer %list.
       *  @param  __l  std::initializer_list.
       */
      basic_string&
      operator=(initializer_list<_CharT> __l)
      {
    this->assign(__l.begin(), __l.size());
    return *this;
      }
#endif // C++11

      // Iterators:
      /**
       *  Returns a read/write iterator that points to the first character in
       *  the %string.  Unshares the string.
       */
      iterator
      begin() _GLIBCXX_NOEXCEPT
      {
    _M_leak();
    return iterator(_M_data());
      }

      /**
       *  Returns a read-only (constant) iterator that points to the first
       *  character in the %string.
       */
      const_iterator
      begin() const _GLIBCXX_NOEXCEPT
      { return const_iterator(_M_data()); }

      /**
       *  Returns a read/write iterator that points one past the last
       *  character in the %string.  Unshares the string.
       */
      iterator
      end() _GLIBCXX_NOEXCEPT
      {
    _M_leak();
    return iterator(_M_data() + this->size());
      }

      /**
       *  Returns a read-only (constant) iterator that points one past the
       *  last character in the %string.
       */
      const_iterator
      end() const _GLIBCXX_NOEXCEPT
      { return const_iterator(_M_data() + this->size()); }

      /**
       *  Returns a read/write reverse iterator that points to the last
       *  character in the %string.  Iteration is done in reverse element
       *  order.  Unshares the string.
       */
      reverse_iterator
      rbegin() _GLIBCXX_NOEXCEPT
      { return reverse_iterator(this->end()); }

      /**
       *  Returns a read-only (constant) reverse iterator that points
       *  to the last character in the %string.  Iteration is done in
       *  reverse element order.
       */
      const_reverse_iterator
      rbegin() const _GLIBCXX_NOEXCEPT
      { return const_reverse_iterator(this->end()); }

      /**
       *  Returns a read/write reverse iterator that points to one before the
       *  first character in the %string.  Iteration is done in reverse
       *  element order.  Unshares the string.
       */
      reverse_iterator
      rend() _GLIBCXX_NOEXCEPT
      { return reverse_iterator(this->begin()); }

      /**
       *  Returns a read-only (constant) reverse iterator that points
       *  to one before the first character in the %string.  Iteration
       *  is done in reverse element order.
       */
      const_reverse_iterator
      rend() const _GLIBCXX_NOEXCEPT
      { return const_reverse_iterator(this->begin()); }

#if __cplusplus >= 201103L
      /**
       *  Returns a read-only (constant) iterator that points to the first
       *  character in the %string.
       */
      const_iterator
      cbegin() const noexcept
      { return const_iterator(this->_M_data()); }

      /**
       *  Returns a read-only (constant) iterator that points one past the
       *  last character in the %string.
       */
      const_iterator
      cend() const noexcept
      { return const_iterator(this->_M_data() + this->size()); }

      /**
       *  Returns a read-only (constant) reverse iterator that points
       *  to the last character in the %string.  Iteration is done in
       *  reverse element order.
       */
      const_reverse_iterator
      crbegin() const noexcept
      { return const_reverse_iterator(this->end()); }

      /**
       *  Returns a read-only (constant) reverse iterator that points
       *  to one before the first character in the %string.  Iteration
       *  is done in reverse element order.
       */
      const_reverse_iterator
      crend() const noexcept
      { return const_reverse_iterator(this->begin()); }
#endif

    public:
      // Capacity:
      ///  Returns the number of characters in the string, not including any
      ///  null-termination.
      size_type
      size() const _GLIBCXX_NOEXCEPT
      { return _M_rep()->_M_length; }

      ///  Returns the number of characters in the string, not including any
      ///  null-termination.
      size_type
      length() const _GLIBCXX_NOEXCEPT
      { return _M_rep()->_M_length; }

      ///  Returns the size() of the largest possible %string.
      size_type
      max_size() const _GLIBCXX_NOEXCEPT
      { return _Rep::_S_max_size; }

      /**
       *  @brief  Resizes the %string to the specified number of characters.
       *  @param  __n  Number of characters the %string should contain.
       *  @param  __c  Character to fill any new elements.
       *
       *  This function will %resize the %string to the specified
       *  number of characters.  If the number is smaller than the
       *  %string's current size the %string is truncated, otherwise
       *  the %string is extended and new elements are %set to @a __c.
       */
      void
      resize(size_type __n, _CharT __c);

      /**
       *  @brief  Resizes the %string to the specified number of characters.
       *  @param  __n  Number of characters the %string should contain.
       *
       *  This function will resize the %string to the specified length.  If
       *  the new size is smaller than the %string's current size the %string
       *  is truncated, otherwise the %string is extended and new characters
       *  are default-constructed.  For basic types such as char, this means
       *  setting them to 0.
       */
      void
      resize(size_type __n)
      { this->resize(__n, _CharT()); }

#if __cplusplus >= 201103L
      ///  A non-binding request to reduce capacity() to size().
      void
      shrink_to_fit()
      {
    if (capacity() > size())
      {
        __try
          { reserve(0); }
        __catch(...)
          { }
      }
      }
#endif

      /**
       *  Returns the total number of characters that the %string can hold
       *  before needing to allocate more memory.
       */
      size_type
      capacity() const _GLIBCXX_NOEXCEPT
      { return _M_rep()->_M_capacity; }

      /**
       *  @brief  Attempt to preallocate enough memory for specified number of
       *          characters.
       *  @param  __res_arg  Number of characters required.
       *  @throw  std::length_error  If @a __res_arg exceeds @c max_size().
       *
       *  This function attempts to reserve enough memory for the
       *  %string to hold the specified number of characters.  If the
       *  number requested is more than max_size(), length_error is
       *  thrown.
       *
       *  The advantage of this function is that if optimal code is a
       *  necessity and the user can determine the string length that will be
       *  required, the user can reserve the memory in %advance, and thus
       *  prevent a possible reallocation of memory and copying of %string
       *  data.
       */
      void
      reserve(size_type __res_arg = 0);

      /**
       *  Erases the string, making it empty.
       */
      void
      clear() _GLIBCXX_NOEXCEPT
      { _M_mutate(0, this->size(), 0); }

      /**
       *  Returns true if the %string is empty.  Equivalent to 
       *  <code>*this == ""</code>.
       */
      bool
      empty() const _GLIBCXX_NOEXCEPT
      { return this->size() == 0; }

      // Element access:
      /**
       *  @brief  Subscript access to the data contained in the %string.
       *  @param  __pos  The index of the character to access.
       *  @return  Read-only (constant) reference to the character.
       *
       *  This operator allows for easy, array-style, data access.
       *  Note that data access with this operator is unchecked and
       *  out_of_range lookups are not defined. (For checked lookups
       *  see at().)
       */
      const_reference
      operator[] (size_type __pos) const
      {
    _GLIBCXX_DEBUG_ASSERT(__pos <= size());
    return _M_data()[__pos];
      }

      /**
       *  @brief  Subscript access to the data contained in the %string.
       *  @param  __pos  The index of the character to access.
       *  @return  Read/write reference to the character.
       *
       *  This operator allows for easy, array-style, data access.
       *  Note that data access with this operator is unchecked and
       *  out_of_range lookups are not defined. (For checked lookups
       *  see at().)  Unshares the string.
       */
      reference
      operator[](size_type __pos)
      {
        // allow pos == size() as v3 extension:
    _GLIBCXX_DEBUG_ASSERT(__pos <= size());
        // but be strict in pedantic mode:
    _GLIBCXX_DEBUG_PEDASSERT(__pos < size());
    _M_leak();
    return _M_data()[__pos];
      }

      /**
       *  @brief  Provides access to the data contained in the %string.
       *  @param __n The index of the character to access.
       *  @return  Read-only (const) reference to the character.
       *  @throw  std::out_of_range  If @a n is an invalid index.
       *
       *  This function provides for safer data access.  The parameter is
       *  first checked that it is in the range of the string.  The function
       *  throws out_of_range if the check fails.
       */
      const_reference
      at(size_type __n) const
      {
    if (__n >= this->size())
      __throw_out_of_range(__N("basic_string::at"));
    return _M_data()[__n];
      }

      /**
       *  @brief  Provides access to the data contained in the %string.
       *  @param __n The index of the character to access.
       *  @return  Read/write reference to the character.
       *  @throw  std::out_of_range  If @a n is an invalid index.
       *
       *  This function provides for safer data access.  The parameter is
       *  first checked that it is in the range of the string.  The function
       *  throws out_of_range if the check fails.  Success results in
       *  unsharing the string.
       */
      reference
      at(size_type __n)
      {
    if (__n >= size())
      __throw_out_of_range(__N("basic_string::at"));
    _M_leak();
    return _M_data()[__n];
      }

#if __cplusplus >= 201103L
      /**
       *  Returns a read/write reference to the data at the first
       *  element of the %string.
       */
      reference
      front()
      { return operator[](0); }

      /**
       *  Returns a read-only (constant) reference to the data at the first
       *  element of the %string.
       */
      const_reference
      front() const
      { return operator[](0); }

      /**
       *  Returns a read/write reference to the data at the last
       *  element of the %string.
       */
      reference
      back()
      { return operator[](this->size() - 1); }

      /**
       *  Returns a read-only (constant) reference to the data at the
       *  last element of the %string.
       */
      const_reference
      back() const
      { return operator[](this->size() - 1); }
#endif

      // Modifiers:
      /**
       *  @brief  Append a string to this string.
       *  @param __str  The string to append.
       *  @return  Reference to this string.
       */
      basic_string&
      operator+=(const basic_string& __str)
      { return this->append(__str); }

      /**
       *  @brief  Append a C string.
       *  @param __s  The C string to append.
       *  @return  Reference to this string.
       */
      basic_string&
      operator+=(const _CharT* __s)
      { return this->append(__s); }

      /**
       *  @brief  Append a character.
       *  @param __c  The character to append.
       *  @return  Reference to this string.
       */
      basic_string&
      operator+=(_CharT __c)
      { 
    this->push_back(__c);
    return *this;
      }

#if __cplusplus >= 201103L
      /**
       *  @brief  Append an initializer_list of characters.
       *  @param __l  The initializer_list of characters to be appended.
       *  @return  Reference to this string.
       */
      basic_string&
      operator+=(initializer_list<_CharT> __l)
      { return this->append(__l.begin(), __l.size()); }
#endif // C++11

      /**
       *  @brief  Append a string to this string.
       *  @param __str  The string to append.
       *  @return  Reference to this string.
       */
      basic_string&
      append(const basic_string& __str);

      /**
       *  @brief  Append a substring.
       *  @param __str  The string to append.
       *  @param __pos  Index of the first character of str to append.
       *  @param __n  The number of characters to append.
       *  @return  Reference to this string.
       *  @throw  std::out_of_range if @a __pos is not a valid index.
       *
       *  This function appends @a __n characters from @a __str
       *  starting at @a __pos to this string.  If @a __n is is larger
       *  than the number of available characters in @a __str, the
       *  remainder of @a __str is appended.
       */
      basic_string&
      append(const basic_string& __str, size_type __pos, size_type __n);

      /**
       *  @brief  Append a C substring.
       *  @param __s  The C string to append.
       *  @param __n  The number of characters to append.
       *  @return  Reference to this string.
       */
      basic_string&
      append(const _CharT* __s, size_type __n);

      /**
       *  @brief  Append a C string.
       *  @param __s  The C string to append.
       *  @return  Reference to this string.
       */
      basic_string&
      append(const _CharT* __s)
      {
    __glibcxx_requires_string(__s);
    return this->append(__s, traits_type::length(__s));
      }

      /**
       *  @brief  Append multiple characters.
       *  @param __n  The number of characters to append.
       *  @param __c  The character to use.
       *  @return  Reference to this string.
       *
       *  Appends __n copies of __c to this string.
       */
      basic_string&
      append(size_type __n, _CharT __c);

#if __cplusplus >= 201103L
      /**
       *  @brief  Append an initializer_list of characters.
       *  @param __l  The initializer_list of characters to append.
       *  @return  Reference to this string.
       */
      basic_string&
      append(initializer_list<_CharT> __l)
      { return this->append(__l.begin(), __l.size()); }
#endif // C++11

      /**
       *  @brief  Append a range of characters.
       *  @param __first  Iterator referencing the first character to append.
       *  @param __last  Iterator marking the end of the range.
       *  @return  Reference to this string.
       *
       *  Appends characters in the range [__first,__last) to this string.
       */
      template<class _InputIterator>
        basic_string&
        append(_InputIterator __first, _InputIterator __last)
        { return this->replace(_M_iend(), _M_iend(), __first, __last); }

      /**
       *  @brief  Append a single character.
       *  @param __c  Character to append.
       */
      void
      push_back(_CharT __c)
      { 
    const size_type __len = 1 + this->size();
    if (__len > this->capacity() || _M_rep()->_M_is_shared())
      this->reserve(__len);
    traits_type::assign(_M_data()[this->size()], __c);
    _M_rep()->_M_set_length_and_sharable(__len);
      }

      /**
       *  @brief  Set value to contents of another string.
       *  @param  __str  Source string to use.
       *  @return  Reference to this string.
       */
      basic_string&
      assign(const basic_string& __str);

#if __cplusplus >= 201103L
      /**
       *  @brief  Set value to contents of another string.
       *  @param  __str  Source string to use.
       *  @return  Reference to this string.
       *
       *  This function sets this string to the exact contents of @a __str.
       *  @a __str is a valid, but unspecified string.
       */
      basic_string&
      assign(basic_string&& __str)
      {
    this->swap(__str);
    return *this;
      }
#endif // C++11

      /**
       *  @brief  Set value to a substring of a string.
       *  @param __str  The string to use.
       *  @param __pos  Index of the first character of str.
       *  @param __n  Number of characters to use.
       *  @return  Reference to this string.
       *  @throw  std::out_of_range if @a pos is not a valid index.
       *
       *  This function sets this string to the substring of @a __str
       *  consisting of @a __n characters at @a __pos.  If @a __n is
       *  is larger than the number of available characters in @a
       *  __str, the remainder of @a __str is used.
       */
      basic_string&
      assign(const basic_string& __str, size_type __pos, size_type __n)
      { return this->assign(__str._M_data()
                + __str._M_check(__pos, "basic_string::assign"),
                __str._M_limit(__pos, __n)); }

      /**
       *  @brief  Set value to a C substring.
       *  @param __s  The C string to use.
       *  @param __n  Number of characters to use.
       *  @return  Reference to this string.
       *
       *  This function sets the value of this string to the first @a __n
       *  characters of @a __s.  If @a __n is is larger than the number of
       *  available characters in @a __s, the remainder of @a __s is used.
       */
      basic_string&
      assign(const _CharT* __s, size_type __n);

      /**
       *  @brief  Set value to contents of a C string.
       *  @param __s  The C string to use.
       *  @return  Reference to this string.
       *
       *  This function sets the value of this string to the value of @a __s.
       *  The data is copied, so there is no dependence on @a __s once the
       *  function returns.
       */
      basic_string&
      assign(const _CharT* __s)
      {
    __glibcxx_requires_string(__s);
    return this->assign(__s, traits_type::length(__s));
      }

      /**
       *  @brief  Set value to multiple characters.
       *  @param __n  Length of the resulting string.
       *  @param __c  The character to use.
       *  @return  Reference to this string.
       *
       *  This function sets the value of this string to @a __n copies of
       *  character @a __c.
       */
      basic_string&
      assign(size_type __n, _CharT __c)
      { return _M_replace_aux(size_type(0), this->size(), __n, __c); }

      /**
       *  @brief  Set value to a range of characters.
       *  @param __first  Iterator referencing the first character to append.
       *  @param __last  Iterator marking the end of the range.
       *  @return  Reference to this string.
       *
       *  Sets value of string to characters in the range [__first,__last).
      */
      template<class _InputIterator>
        basic_string&
        assign(_InputIterator __first, _InputIterator __last)
        { return this->replace(_M_ibegin(), _M_iend(), __first, __last); }

#if __cplusplus >= 201103L
      /**
       *  @brief  Set value to an initializer_list of characters.
       *  @param __l  The initializer_list of characters to assign.
       *  @return  Reference to this string.
       */
      basic_string&
      assign(initializer_list<_CharT> __l)
      { return this->assign(__l.begin(), __l.size()); }
#endif // C++11

      /**
       *  @brief  Insert multiple characters.
       *  @param __p  Iterator referencing location in string to insert at.
       *  @param __n  Number of characters to insert
       *  @param __c  The character to insert.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *
       *  Inserts @a __n copies of character @a __c starting at the
       *  position referenced by iterator @a __p.  If adding
       *  characters causes the length to exceed max_size(),
       *  length_error is thrown.  The value of the string doesn't
       *  change if an error is thrown.
      */
      void
      insert(iterator __p, size_type __n, _CharT __c)
      { this->replace(__p, __p, __n, __c);  }

      /**
       *  @brief  Insert a range of characters.
       *  @param __p  Iterator referencing location in string to insert at.
       *  @param __beg  Start of range.
       *  @param __end  End of range.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *
       *  Inserts characters in range [__beg,__end).  If adding
       *  characters causes the length to exceed max_size(),
       *  length_error is thrown.  The value of the string doesn't
       *  change if an error is thrown.
      */
      template<class _InputIterator>
        void
        insert(iterator __p, _InputIterator __beg, _InputIterator __end)
        { this->replace(__p, __p, __beg, __end); }

#if __cplusplus >= 201103L
      /**
       *  @brief  Insert an initializer_list of characters.
       *  @param __p  Iterator referencing location in string to insert at.
       *  @param __l  The initializer_list of characters to insert.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       */
      void
      insert(iterator __p, initializer_list<_CharT> __l)
      {
    _GLIBCXX_DEBUG_PEDASSERT(__p >= _M_ibegin() && __p <= _M_iend());
    this->insert(__p - _M_ibegin(), __l.begin(), __l.size());
      }
#endif // C++11

      /**
       *  @brief  Insert value of a string.
       *  @param __pos1  Iterator referencing location in string to insert at.
       *  @param __str  The string to insert.
       *  @return  Reference to this string.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *
       *  Inserts value of @a __str starting at @a __pos1.  If adding
       *  characters causes the length to exceed max_size(),
       *  length_error is thrown.  The value of the string doesn't
       *  change if an error is thrown.
      */
      basic_string&
      insert(size_type __pos1, const basic_string& __str)
      { return this->insert(__pos1, __str, size_type(0), __str.size()); }

      /**
       *  @brief  Insert a substring.
       *  @param __pos1  Iterator referencing location in string to insert at.
       *  @param __str  The string to insert.
       *  @param __pos2  Start of characters in str to insert.
       *  @param __n  Number of characters to insert.
       *  @return  Reference to this string.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *  @throw  std::out_of_range  If @a pos1 > size() or
       *  @a __pos2 > @a str.size().
       *
       *  Starting at @a pos1, insert @a __n character of @a __str
       *  beginning with @a __pos2.  If adding characters causes the
       *  length to exceed max_size(), length_error is thrown.  If @a
       *  __pos1 is beyond the end of this string or @a __pos2 is
       *  beyond the end of @a __str, out_of_range is thrown.  The
       *  value of the string doesn't change if an error is thrown.
      */
      basic_string&
      insert(size_type __pos1, const basic_string& __str,
         size_type __pos2, size_type __n)
      { return this->insert(__pos1, __str._M_data()
                + __str._M_check(__pos2, "basic_string::insert"),
                __str._M_limit(__pos2, __n)); }

      /**
       *  @brief  Insert a C substring.
       *  @param __pos  Iterator referencing location in string to insert at.
       *  @param __s  The C string to insert.
       *  @param __n  The number of characters to insert.
       *  @return  Reference to this string.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *  @throw  std::out_of_range  If @a __pos is beyond the end of this
       *  string.
       *
       *  Inserts the first @a __n characters of @a __s starting at @a
       *  __pos.  If adding characters causes the length to exceed
       *  max_size(), length_error is thrown.  If @a __pos is beyond
       *  end(), out_of_range is thrown.  The value of the string
       *  doesn't change if an error is thrown.
      */
      basic_string&
      insert(size_type __pos, const _CharT* __s, size_type __n);

      /**
       *  @brief  Insert a C string.
       *  @param __pos  Iterator referencing location in string to insert at.
       *  @param __s  The C string to insert.
       *  @return  Reference to this string.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *  @throw  std::out_of_range  If @a pos is beyond the end of this
       *  string.
       *
       *  Inserts the first @a n characters of @a __s starting at @a __pos.  If
       *  adding characters causes the length to exceed max_size(),
       *  length_error is thrown.  If @a __pos is beyond end(), out_of_range is
       *  thrown.  The value of the string doesn't change if an error is
       *  thrown.
      */
      basic_string&
      insert(size_type __pos, const _CharT* __s)
      {
    __glibcxx_requires_string(__s);
    return this->insert(__pos, __s, traits_type::length(__s));
      }

      /**
       *  @brief  Insert multiple characters.
       *  @param __pos  Index in string to insert at.
       *  @param __n  Number of characters to insert
       *  @param __c  The character to insert.
       *  @return  Reference to this string.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *  @throw  std::out_of_range  If @a __pos is beyond the end of this
       *  string.
       *
       *  Inserts @a __n copies of character @a __c starting at index
       *  @a __pos.  If adding characters causes the length to exceed
       *  max_size(), length_error is thrown.  If @a __pos > length(),
       *  out_of_range is thrown.  The value of the string doesn't
       *  change if an error is thrown.
      */
      basic_string&
      insert(size_type __pos, size_type __n, _CharT __c)
      { return _M_replace_aux(_M_check(__pos, "basic_string::insert"),
                  size_type(0), __n, __c); }

      /**
       *  @brief  Insert one character.
       *  @param __p  Iterator referencing position in string to insert at.
       *  @param __c  The character to insert.
       *  @return  Iterator referencing newly inserted char.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *
       *  Inserts character @a __c at position referenced by @a __p.
       *  If adding character causes the length to exceed max_size(),
       *  length_error is thrown.  If @a __p is beyond end of string,
       *  out_of_range is thrown.  The value of the string doesn't
       *  change if an error is thrown.
      */
      iterator
      insert(iterator __p, _CharT __c)
      {
    _GLIBCXX_DEBUG_PEDASSERT(__p >= _M_ibegin() && __p <= _M_iend());
    const size_type __pos = __p - _M_ibegin();
    _M_replace_aux(__pos, size_type(0), size_type(1), __c);
    _M_rep()->_M_set_leaked();
    return iterator(_M_data() + __pos);
      }

      /**
       *  @brief  Remove characters.
       *  @param __pos  Index of first character to remove (default 0).
       *  @param __n  Number of characters to remove (default remainder).
       *  @return  Reference to this string.
       *  @throw  std::out_of_range  If @a pos is beyond the end of this
       *  string.
       *
       *  Removes @a __n characters from this string starting at @a
       *  __pos.  The length of the string is reduced by @a __n.  If
       *  there are < @a __n characters to remove, the remainder of
       *  the string is truncated.  If @a __p is beyond end of string,
       *  out_of_range is thrown.  The value of the string doesn't
       *  change if an error is thrown.
      */
      basic_string&
      erase(size_type __pos = 0, size_type __n = npos)
      { 
    _M_mutate(_M_check(__pos, "basic_string::erase"),
          _M_limit(__pos, __n), size_type(0));
    return *this;
      }

      /**
       *  @brief  Remove one character.
       *  @param __position  Iterator referencing the character to remove.
       *  @return  iterator referencing same location after removal.
       *
       *  Removes the character at @a __position from this string. The value
       *  of the string doesn't change if an error is thrown.
      */
      iterator
      erase(iterator __position)
      {
    _GLIBCXX_DEBUG_PEDASSERT(__position >= _M_ibegin()
                 && __position < _M_iend());
    const size_type __pos = __position - _M_ibegin();
    _M_mutate(__pos, size_type(1), size_type(0));
    _M_rep()->_M_set_leaked();
    return iterator(_M_data() + __pos);
      }

      /**
       *  @brief  Remove a range of characters.
       *  @param __first  Iterator referencing the first character to remove.
       *  @param __last  Iterator referencing the end of the range.
       *  @return  Iterator referencing location of first after removal.
       *
       *  Removes the characters in the range [first,last) from this string.
       *  The value of the string doesn't change if an error is thrown.
      */
      iterator
      erase(iterator __first, iterator __last);
 
#if __cplusplus >= 201103L
      /**
       *  @brief  Remove the last character.
       *
       *  The string must be non-empty.
       */
      void
      pop_back()
      { erase(size()-1, 1); }
#endif // C++11

      /**
       *  @brief  Replace characters with value from another string.
       *  @param __pos  Index of first character to replace.
       *  @param __n  Number of characters to be replaced.
       *  @param __str  String to insert.
       *  @return  Reference to this string.
       *  @throw  std::out_of_range  If @a pos is beyond the end of this
       *  string.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *
       *  Removes the characters in the range [__pos,__pos+__n) from
       *  this string.  In place, the value of @a __str is inserted.
       *  If @a __pos is beyond end of string, out_of_range is thrown.
       *  If the length of the result exceeds max_size(), length_error
       *  is thrown.  The value of the string doesn't change if an
       *  error is thrown.
      */
      basic_string&
      replace(size_type __pos, size_type __n, const basic_string& __str)
      { return this->replace(__pos, __n, __str._M_data(), __str.size()); }

      /**
       *  @brief  Replace characters with value from another string.
       *  @param __pos1  Index of first character to replace.
       *  @param __n1  Number of characters to be replaced.
       *  @param __str  String to insert.
       *  @param __pos2  Index of first character of str to use.
       *  @param __n2  Number of characters from str to use.
       *  @return  Reference to this string.
       *  @throw  std::out_of_range  If @a __pos1 > size() or @a __pos2 >
       *  __str.size().
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *
       *  Removes the characters in the range [__pos1,__pos1 + n) from this
       *  string.  In place, the value of @a __str is inserted.  If @a __pos is
       *  beyond end of string, out_of_range is thrown.  If the length of the
       *  result exceeds max_size(), length_error is thrown.  The value of the
       *  string doesn't change if an error is thrown.
      */
      basic_string&
      replace(size_type __pos1, size_type __n1, const basic_string& __str,
          size_type __pos2, size_type __n2)
      { return this->replace(__pos1, __n1, __str._M_data()
                 + __str._M_check(__pos2, "basic_string::replace"),
                 __str._M_limit(__pos2, __n2)); }

      /**
       *  @brief  Replace characters with value of a C substring.
       *  @param __pos  Index of first character to replace.
       *  @param __n1  Number of characters to be replaced.
       *  @param __s  C string to insert.
       *  @param __n2  Number of characters from @a s to use.
       *  @return  Reference to this string.
       *  @throw  std::out_of_range  If @a pos1 > size().
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *
       *  Removes the characters in the range [__pos,__pos + __n1)
       *  from this string.  In place, the first @a __n2 characters of
       *  @a __s are inserted, or all of @a __s if @a __n2 is too large.  If
       *  @a __pos is beyond end of string, out_of_range is thrown.  If
       *  the length of result exceeds max_size(), length_error is
       *  thrown.  The value of the string doesn't change if an error
       *  is thrown.
      */
      basic_string&
      replace(size_type __pos, size_type __n1, const _CharT* __s,
          size_type __n2);

      /**
       *  @brief  Replace characters with value of a C string.
       *  @param __pos  Index of first character to replace.
       *  @param __n1  Number of characters to be replaced.
       *  @param __s  C string to insert.
       *  @return  Reference to this string.
       *  @throw  std::out_of_range  If @a pos > size().
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *
       *  Removes the characters in the range [__pos,__pos + __n1)
       *  from this string.  In place, the characters of @a __s are
       *  inserted.  If @a __pos is beyond end of string, out_of_range
       *  is thrown.  If the length of result exceeds max_size(),
       *  length_error is thrown.  The value of the string doesn't
       *  change if an error is thrown.
      */
      basic_string&
      replace(size_type __pos, size_type __n1, const _CharT* __s)
      {
    __glibcxx_requires_string(__s);
    return this->replace(__pos, __n1, __s, traits_type::length(__s));
      }

      /**
       *  @brief  Replace characters with multiple characters.
       *  @param __pos  Index of first character to replace.
       *  @param __n1  Number of characters to be replaced.
       *  @param __n2  Number of characters to insert.
       *  @param __c  Character to insert.
       *  @return  Reference to this string.
       *  @throw  std::out_of_range  If @a __pos > size().
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *
       *  Removes the characters in the range [pos,pos + n1) from this
       *  string.  In place, @a __n2 copies of @a __c are inserted.
       *  If @a __pos is beyond end of string, out_of_range is thrown.
       *  If the length of result exceeds max_size(), length_error is
       *  thrown.  The value of the string doesn't change if an error
       *  is thrown.
      */
      basic_string&
      replace(size_type __pos, size_type __n1, size_type __n2, _CharT __c)
      { return _M_replace_aux(_M_check(__pos, "basic_string::replace"),
                  _M_limit(__pos, __n1), __n2, __c); }

      /**
       *  @brief  Replace range of characters with string.
       *  @param __i1  Iterator referencing start of range to replace.
       *  @param __i2  Iterator referencing end of range to replace.
       *  @param __str  String value to insert.
       *  @return  Reference to this string.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *
       *  Removes the characters in the range [__i1,__i2).  In place,
       *  the value of @a __str is inserted.  If the length of result
       *  exceeds max_size(), length_error is thrown.  The value of
       *  the string doesn't change if an error is thrown.
      */
      basic_string&
      replace(iterator __i1, iterator __i2, const basic_string& __str)
      { return this->replace(__i1, __i2, __str._M_data(), __str.size()); }

      /**
       *  @brief  Replace range of characters with C substring.
       *  @param __i1  Iterator referencing start of range to replace.
       *  @param __i2  Iterator referencing end of range to replace.
       *  @param __s  C string value to insert.
       *  @param __n  Number of characters from s to insert.
       *  @return  Reference to this string.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *
       *  Removes the characters in the range [__i1,__i2).  In place,
       *  the first @a __n characters of @a __s are inserted.  If the
       *  length of result exceeds max_size(), length_error is thrown.
       *  The value of the string doesn't change if an error is
       *  thrown.
      */
      basic_string&
      replace(iterator __i1, iterator __i2, const _CharT* __s, size_type __n)
      {
    _GLIBCXX_DEBUG_PEDASSERT(_M_ibegin() <= __i1 && __i1 <= __i2
                 && __i2 <= _M_iend());
    return this->replace(__i1 - _M_ibegin(), __i2 - __i1, __s, __n);
      }

      /**
       *  @brief  Replace range of characters with C string.
       *  @param __i1  Iterator referencing start of range to replace.
       *  @param __i2  Iterator referencing end of range to replace.
       *  @param __s  C string value to insert.
       *  @return  Reference to this string.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *
       *  Removes the characters in the range [__i1,__i2).  In place,
       *  the characters of @a __s are inserted.  If the length of
       *  result exceeds max_size(), length_error is thrown.  The
       *  value of the string doesn't change if an error is thrown.
      */
      basic_string&
      replace(iterator __i1, iterator __i2, const _CharT* __s)
      {
    __glibcxx_requires_string(__s);
    return this->replace(__i1, __i2, __s, traits_type::length(__s));
      }

      /**
       *  @brief  Replace range of characters with multiple characters
       *  @param __i1  Iterator referencing start of range to replace.
       *  @param __i2  Iterator referencing end of range to replace.
       *  @param __n  Number of characters to insert.
       *  @param __c  Character to insert.
       *  @return  Reference to this string.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *
       *  Removes the characters in the range [__i1,__i2).  In place,
       *  @a __n copies of @a __c are inserted.  If the length of
       *  result exceeds max_size(), length_error is thrown.  The
       *  value of the string doesn't change if an error is thrown.
      */
      basic_string&
      replace(iterator __i1, iterator __i2, size_type __n, _CharT __c)
      {
    _GLIBCXX_DEBUG_PEDASSERT(_M_ibegin() <= __i1 && __i1 <= __i2
                 && __i2 <= _M_iend());
    return _M_replace_aux(__i1 - _M_ibegin(), __i2 - __i1, __n, __c);
      }

      /**
       *  @brief  Replace range of characters with range.
       *  @param __i1  Iterator referencing start of range to replace.
       *  @param __i2  Iterator referencing end of range to replace.
       *  @param __k1  Iterator referencing start of range to insert.
       *  @param __k2  Iterator referencing end of range to insert.
       *  @return  Reference to this string.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *
       *  Removes the characters in the range [__i1,__i2).  In place,
       *  characters in the range [__k1,__k2) are inserted.  If the
       *  length of result exceeds max_size(), length_error is thrown.
       *  The value of the string doesn't change if an error is
       *  thrown.
      */
      template<class _InputIterator>
        basic_string&
        replace(iterator __i1, iterator __i2,
        _InputIterator __k1, _InputIterator __k2)
        {
      _GLIBCXX_DEBUG_PEDASSERT(_M_ibegin() <= __i1 && __i1 <= __i2
                   && __i2 <= _M_iend());
      __glibcxx_requires_valid_range(__k1, __k2);
      typedef typename std::__is_integer<_InputIterator>::__type _Integral;
      return _M_replace_dispatch(__i1, __i2, __k1, __k2, _Integral());
    }

      // Specializations for the common case of pointer and iterator:
      // useful to avoid the overhead of temporary buffering in _M_replace.
      basic_string&
      replace(iterator __i1, iterator __i2, _CharT* __k1, _CharT* __k2)
      {
    _GLIBCXX_DEBUG_PEDASSERT(_M_ibegin() <= __i1 && __i1 <= __i2
                 && __i2 <= _M_iend());
    __glibcxx_requires_valid_range(__k1, __k2);
    return this->replace(__i1 - _M_ibegin(), __i2 - __i1,
                 __k1, __k2 - __k1);
      }

      basic_string&
      replace(iterator __i1, iterator __i2,
          const _CharT* __k1, const _CharT* __k2)
      {
    _GLIBCXX_DEBUG_PEDASSERT(_M_ibegin() <= __i1 && __i1 <= __i2
                 && __i2 <= _M_iend());
    __glibcxx_requires_valid_range(__k1, __k2);
    return this->replace(__i1 - _M_ibegin(), __i2 - __i1,
                 __k1, __k2 - __k1);
      }

      basic_string&
      replace(iterator __i1, iterator __i2, iterator __k1, iterator __k2)
      {
    _GLIBCXX_DEBUG_PEDASSERT(_M_ibegin() <= __i1 && __i1 <= __i2
                 && __i2 <= _M_iend());
    __glibcxx_requires_valid_range(__k1, __k2);
    return this->replace(__i1 - _M_ibegin(), __i2 - __i1,
                 __k1.base(), __k2 - __k1);
      }

      basic_string&
      replace(iterator __i1, iterator __i2,
          const_iterator __k1, const_iterator __k2)
      {
    _GLIBCXX_DEBUG_PEDASSERT(_M_ibegin() <= __i1 && __i1 <= __i2
                 && __i2 <= _M_iend());
    __glibcxx_requires_valid_range(__k1, __k2);
    return this->replace(__i1 - _M_ibegin(), __i2 - __i1,
                 __k1.base(), __k2 - __k1);
      }
      
#if __cplusplus >= 201103L
      /**
       *  @brief  Replace range of characters with initializer_list.
       *  @param __i1  Iterator referencing start of range to replace.
       *  @param __i2  Iterator referencing end of range to replace.
       *  @param __l  The initializer_list of characters to insert.
       *  @return  Reference to this string.
       *  @throw  std::length_error  If new length exceeds @c max_size().
       *
       *  Removes the characters in the range [__i1,__i2).  In place,
       *  characters in the range [__k1,__k2) are inserted.  If the
       *  length of result exceeds max_size(), length_error is thrown.
       *  The value of the string doesn't change if an error is
       *  thrown.
      */
      basic_string& replace(iterator __i1, iterator __i2,
                initializer_list<_CharT> __l)
      { return this->replace(__i1, __i2, __l.begin(), __l.end()); }
#endif // C++11

    private:
      template<class _Integer>
    basic_string&
    _M_replace_dispatch(iterator __i1, iterator __i2, _Integer __n,
                _Integer __val, __true_type)
        { return _M_replace_aux(__i1 - _M_ibegin(), __i2 - __i1, __n, __val); }

      template<class _InputIterator>
    basic_string&
    _M_replace_dispatch(iterator __i1, iterator __i2, _InputIterator __k1,
                _InputIterator __k2, __false_type);

      basic_string&
      _M_replace_aux(size_type __pos1, size_type __n1, size_type __n2,
             _CharT __c);

      basic_string&
      _M_replace_safe(size_type __pos1, size_type __n1, const _CharT* __s,
              size_type __n2);

      // _S_construct_aux is used to implement the 21.3.1 para 15 which
      // requires special behaviour if _InIter is an integral type
      template<class _InIterator>
        static _CharT*
        _S_construct_aux(_InIterator __beg, _InIterator __end,
             const _Alloc& __a, __false_type)
    {
          typedef typename iterator_traits<_InIterator>::iterator_category _Tag;
          return _S_construct(__beg, __end, __a, _Tag());
    }

      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 438. Ambiguity in the "do the right thing" clause
      template<class _Integer>
        static _CharT*
        _S_construct_aux(_Integer __beg, _Integer __end,
             const _Alloc& __a, __true_type)
        { return _S_construct_aux_2(static_cast<size_type>(__beg),
                    __end, __a); }

      static _CharT*
      _S_construct_aux_2(size_type __req, _CharT __c, const _Alloc& __a)
      { return _S_construct(__req, __c, __a); }

      template<class _InIterator>
        static _CharT*
        _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a)
    {
      typedef typename std::__is_integer<_InIterator>::__type _Integral;
      return _S_construct_aux(__beg, __end, __a, _Integral());
        }

      // For Input Iterators, used in istreambuf_iterators, etc.
      template<class _InIterator>
        static _CharT*
         _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
              input_iterator_tag);

      // For forward_iterators up to random_access_iterators, used for
      // string::iterator, _CharT*, etc.
      template<class _FwdIterator>
        static _CharT*
        _S_construct(_FwdIterator __beg, _FwdIterator __end, const _Alloc& __a,
             forward_iterator_tag);

      static _CharT*
      _S_construct(size_type __req, _CharT __c, const _Alloc& __a);

    public:

      /**
       *  @brief  Copy substring into C string.
       *  @param __s  C string to copy value into.
       *  @param __n  Number of characters to copy.
       *  @param __pos  Index of first character to copy.
       *  @return  Number of characters actually copied
       *  @throw  std::out_of_range  If __pos > size().
       *
       *  Copies up to @a __n characters starting at @a __pos into the
       *  C string @a __s.  If @a __pos is %greater than size(),
       *  out_of_range is thrown.
      */
      size_type
      copy(_CharT* __s, size_type __n, size_type __pos = 0) const;

      /**
       *  @brief  Swap contents with another string.
       *  @param __s  String to swap with.
       *
       *  Exchanges the contents of this string with that of @a __s in constant
       *  time.
      */
      void
      swap(basic_string& __s);

      // String operations:
      /**
       *  @brief  Return const pointer to null-terminated contents.
       *
       *  This is a handle to internal data.  Do not modify or dire things may
       *  happen.
      */
      const _CharT*
      c_str() const _GLIBCXX_NOEXCEPT
      { return _M_data(); }

      /**
       *  @brief  Return const pointer to contents.
       *
       *  This is a handle to internal data.  Do not modify or dire things may
       *  happen.
      */
      const _CharT*
      data() const _GLIBCXX_NOEXCEPT
      { return _M_data(); }

      /**
       *  @brief  Return copy of allocator used to construct this string.
      */
      allocator_type
      get_allocator() const _GLIBCXX_NOEXCEPT
      { return _M_dataplus; }

      /**
       *  @brief  Find position of a C substring.
       *  @param __s  C string to locate.
       *  @param __pos  Index of character to search from.
       *  @param __n  Number of characters from @a s to search for.
       *  @return  Index of start of first occurrence.
       *
       *  Starting from @a __pos, searches forward for the first @a
       *  __n characters in @a __s within this string.  If found,
       *  returns the index where it begins.  If not found, returns
       *  npos.
      */
      size_type
      find(const _CharT* __s, size_type __pos, size_type __n) const;

      /**
       *  @brief  Find position of a string.
       *  @param __str  String to locate.
       *  @param __pos  Index of character to search from (default 0).
       *  @return  Index of start of first occurrence.
       *
       *  Starting from @a __pos, searches forward for value of @a __str within
       *  this string.  If found, returns the index where it begins.  If not
       *  found, returns npos.
      */
      size_type
      find(const basic_string& __str, size_type __pos = 0) const
    _GLIBCXX_NOEXCEPT
      { return this->find(__str.data(), __pos, __str.size()); }

      /**
       *  @brief  Find position of a C string.
       *  @param __s  C string to locate.
       *  @param __pos  Index of character to search from (default 0).
       *  @return  Index of start of first occurrence.
       *
       *  Starting from @a __pos, searches forward for the value of @a
       *  __s within this string.  If found, returns the index where
       *  it begins.  If not found, returns npos.
      */
      size_type
      find(const _CharT* __s, size_type __pos = 0) const
      {
    __glibcxx_requires_string(__s);
    return this->find(__s, __pos, traits_type::length(__s));
      }

      /**
       *  @brief  Find position of a character.
       *  @param __c  Character to locate.
       *  @param __pos  Index of character to search from (default 0).
       *  @return  Index of first occurrence.
       *
       *  Starting from @a __pos, searches forward for @a __c within
       *  this string.  If found, returns the index where it was
       *  found.  If not found, returns npos.
      */
      size_type
      find(_CharT __c, size_type __pos = 0) const _GLIBCXX_NOEXCEPT;

      /**
       *  @brief  Find last position of a string.
       *  @param __str  String to locate.
       *  @param __pos  Index of character to search back from (default end).
       *  @return  Index of start of last occurrence.
       *
       *  Starting from @a __pos, searches backward for value of @a
       *  __str within this string.  If found, returns the index where
       *  it begins.  If not found, returns npos.
      */
      size_type
      rfind(const basic_string& __str, size_type __pos = npos) const
    _GLIBCXX_NOEXCEPT
      { return this->rfind(__str.data(), __pos, __str.size()); }

      /**
       *  @brief  Find last position of a C substring.
       *  @param __s  C string to locate.
       *  @param __pos  Index of character to search back from.
       *  @param __n  Number of characters from s to search for.
       *  @return  Index of start of last occurrence.
       *
       *  Starting from @a __pos, searches backward for the first @a
       *  __n characters in @a __s within this string.  If found,
       *  returns the index where it begins.  If not found, returns
       *  npos.
      */
      size_type
      rfind(const _CharT* __s, size_type __pos, size_type __n) const;

      /**
       *  @brief  Find last position of a C string.
       *  @param __s  C string to locate.
       *  @param __pos  Index of character to start search at (default end).
       *  @return  Index of start of  last occurrence.
       *
       *  Starting from @a __pos, searches backward for the value of
       *  @a __s within this string.  If found, returns the index
       *  where it begins.  If not found, returns npos.
      */
      size_type
      rfind(const _CharT* __s, size_type __pos = npos) const
      {
    __glibcxx_requires_string(__s);
    return this->rfind(__s, __pos, traits_type::length(__s));
      }

      /**
       *  @brief  Find last position of a character.
       *  @param __c  Character to locate.
       *  @param __pos  Index of character to search back from (default end).
       *  @return  Index of last occurrence.
       *
       *  Starting from @a __pos, searches backward for @a __c within
       *  this string.  If found, returns the index where it was
       *  found.  If not found, returns npos.
      */
      size_type
      rfind(_CharT __c, size_type __pos = npos) const _GLIBCXX_NOEXCEPT;

      /**
       *  @brief  Find position of a character of string.
       *  @param __str  String containing characters to locate.
       *  @param __pos  Index of character to search from (default 0).
       *  @return  Index of first occurrence.
       *
       *  Starting from @a __pos, searches forward for one of the
       *  characters of @a __str within this string.  If found,
       *  returns the index where it was found.  If not found, returns
       *  npos.
      */
      size_type
      find_first_of(const basic_string& __str, size_type __pos = 0) const
    _GLIBCXX_NOEXCEPT
      { return this->find_first_of(__str.data(), __pos, __str.size()); }

      /**
       *  @brief  Find position of a character of C substring.
       *  @param __s  String containing characters to locate.
       *  @param __pos  Index of character to search from.
       *  @param __n  Number of characters from s to search for.
       *  @return  Index of first occurrence.
       *
       *  Starting from @a __pos, searches forward for one of the
       *  first @a __n characters of @a __s within this string.  If
       *  found, returns the index where it was found.  If not found,
       *  returns npos.
      */
      size_type
      find_first_of(const _CharT* __s, size_type __pos, size_type __n) const;

      /**
       *  @brief  Find position of a character of C string.
       *  @param __s  String containing characters to locate.
       *  @param __pos  Index of character to search from (default 0).
       *  @return  Index of first occurrence.
       *
       *  Starting from @a __pos, searches forward for one of the
       *  characters of @a __s within this string.  If found, returns
       *  the index where it was found.  If not found, returns npos.
      */
      size_type
      find_first_of(const _CharT* __s, size_type __pos = 0) const
      {
    __glibcxx_requires_string(__s);
    return this->find_first_of(__s, __pos, traits_type::length(__s));
      }

      /**
       *  @brief  Find position of a character.
       *  @param __c  Character to locate.
       *  @param __pos  Index of character to search from (default 0).
       *  @return  Index of first occurrence.
       *
       *  Starting from @a __pos, searches forward for the character
       *  @a __c within this string.  If found, returns the index
       *  where it was found.  If not found, returns npos.
       *
       *  Note: equivalent to find(__c, __pos).
      */
      size_type
      find_first_of(_CharT __c, size_type __pos = 0) const _GLIBCXX_NOEXCEPT
      { return this->find(__c, __pos); }

      /**
       *  @brief  Find last position of a character of string.
       *  @param __str  String containing characters to locate.
       *  @param __pos  Index of character to search back from (default end).
       *  @return  Index of last occurrence.
       *
       *  Starting from @a __pos, searches backward for one of the
       *  characters of @a __str within this string.  If found,
       *  returns the index where it was found.  If not found, returns
       *  npos.
      */
      size_type
      find_last_of(const basic_string& __str, size_type __pos = npos) const
    _GLIBCXX_NOEXCEPT
      { return this->find_last_of(__str.data(), __pos, __str.size()); }

      /**
       *  @brief  Find last position of a character of C substring.
       *  @param __s  C string containing characters to locate.
       *  @param __pos  Index of character to search back from.
       *  @param __n  Number of characters from s to search for.
       *  @return  Index of last occurrence.
       *
       *  Starting from @a __pos, searches backward for one of the
       *  first @a __n characters of @a __s within this string.  If
       *  found, returns the index where it was found.  If not found,
       *  returns npos.
      */
      size_type
      find_last_of(const _CharT* __s, size_type __pos, size_type __n) const;

      /**
       *  @brief  Find last position of a character of C string.
       *  @param __s  C string containing characters to locate.
       *  @param __pos  Index of character to search back from (default end).
       *  @return  Index of last occurrence.
       *
       *  Starting from @a __pos, searches backward for one of the
       *  characters of @a __s within this string.  If found, returns
       *  the index where it was found.  If not found, returns npos.
      */
      size_type
      find_last_of(const _CharT* __s, size_type __pos = npos) const
      {
    __glibcxx_requires_string(__s);
    return this->find_last_of(__s, __pos, traits_type::length(__s));
      }

      /**
       *  @brief  Find last position of a character.
       *  @param __c  Character to locate.
       *  @param __pos  Index of character to search back from (default end).
       *  @return  Index of last occurrence.
       *
       *  Starting from @a __pos, searches backward for @a __c within
       *  this string.  If found, returns the index where it was
       *  found.  If not found, returns npos.
       *
       *  Note: equivalent to rfind(__c, __pos).
      */
      size_type
      find_last_of(_CharT __c, size_type __pos = npos) const _GLIBCXX_NOEXCEPT
      { return this->rfind(__c, __pos); }

      /**
       *  @brief  Find position of a character not in string.
       *  @param __str  String containing characters to avoid.
       *  @param __pos  Index of character to search from (default 0).
       *  @return  Index of first occurrence.
       *
       *  Starting from @a __pos, searches forward for a character not contained
       *  in @a __str within this string.  If found, returns the index where it
       *  was found.  If not found, returns npos.
      */
      size_type
      find_first_not_of(const basic_string& __str, size_type __pos = 0) const
    _GLIBCXX_NOEXCEPT
      { return this->find_first_not_of(__str.data(), __pos, __str.size()); }

      /**
       *  @brief  Find position of a character not in C substring.
       *  @param __s  C string containing characters to avoid.
       *  @param __pos  Index of character to search from.
       *  @param __n  Number of characters from __s to consider.
       *  @return  Index of first occurrence.
       *
       *  Starting from @a __pos, searches forward for a character not
       *  contained in the first @a __n characters of @a __s within
       *  this string.  If found, returns the index where it was
       *  found.  If not found, returns npos.
      */
      size_type
      find_first_not_of(const _CharT* __s, size_type __pos,
            size_type __n) const;

      /**
       *  @brief  Find position of a character not in C string.
       *  @param __s  C string containing characters to avoid.
       *  @param __pos  Index of character to search from (default 0).
       *  @return  Index of first occurrence.
       *
       *  Starting from @a __pos, searches forward for a character not
       *  contained in @a __s within this string.  If found, returns
       *  the index where it was found.  If not found, returns npos.
      */
      size_type
      find_first_not_of(const _CharT* __s, size_type __pos = 0) const
      {
    __glibcxx_requires_string(__s);
    return this->find_first_not_of(__s, __pos, traits_type::length(__s));
      }

      /**
       *  @brief  Find position of a different character.
       *  @param __c  Character to avoid.
       *  @param __pos  Index of character to search from (default 0).
       *  @return  Index of first occurrence.
       *
       *  Starting from @a __pos, searches forward for a character
       *  other than @a __c within this string.  If found, returns the
       *  index where it was found.  If not found, returns npos.
      */
      size_type
      find_first_not_of(_CharT __c, size_type __pos = 0) const
    _GLIBCXX_NOEXCEPT;

      /**
       *  @brief  Find last position of a character not in string.
       *  @param __str  String containing characters to avoid.
       *  @param __pos  Index of character to search back from (default end).
       *  @return  Index of last occurrence.
       *
       *  Starting from @a __pos, searches backward for a character
       *  not contained in @a __str within this string.  If found,
       *  returns the index where it was found.  If not found, returns
       *  npos.
      */
      size_type
      find_last_not_of(const basic_string& __str, size_type __pos = npos) const
    _GLIBCXX_NOEXCEPT
      { return this->find_last_not_of(__str.data(), __pos, __str.size()); }

      /**
       *  @brief  Find last position of a character not in C substring.
       *  @param __s  C string containing characters to avoid.
       *  @param __pos  Index of character to search back from.
       *  @param __n  Number of characters from s to consider.
       *  @return  Index of last occurrence.
       *
       *  Starting from @a __pos, searches backward for a character not
       *  contained in the first @a __n characters of @a __s within this string.
       *  If found, returns the index where it was found.  If not found,
       *  returns npos.
      */
      size_type
      find_last_not_of(const _CharT* __s, size_type __pos,
               size_type __n) const;
      /**
       *  @brief  Find last position of a character not in C string.
       *  @param __s  C string containing characters to avoid.
       *  @param __pos  Index of character to search back from (default end).
       *  @return  Index of last occurrence.
       *
       *  Starting from @a __pos, searches backward for a character
       *  not contained in @a __s within this string.  If found,
       *  returns the index where it was found.  If not found, returns
       *  npos.
      */
      size_type
      find_last_not_of(const _CharT* __s, size_type __pos = npos) const
      {
    __glibcxx_requires_string(__s);
    return this->find_last_not_of(__s, __pos, traits_type::length(__s));
      }

      /**
       *  @brief  Find last position of a different character.
       *  @param __c  Character to avoid.
       *  @param __pos  Index of character to search back from (default end).
       *  @return  Index of last occurrence.
       *
       *  Starting from @a __pos, searches backward for a character other than
       *  @a __c within this string.  If found, returns the index where it was
       *  found.  If not found, returns npos.
      */
      size_type
      find_last_not_of(_CharT __c, size_type __pos = npos) const
    _GLIBCXX_NOEXCEPT;

      /**
       *  @brief  Get a substring.
       *  @param __pos  Index of first character (default 0).
       *  @param __n  Number of characters in substring (default remainder).
       *  @return  The new string.
       *  @throw  std::out_of_range  If __pos > size().
       *
       *  Construct and return a new string using the @a __n
       *  characters starting at @a __pos.  If the string is too
       *  short, use the remainder of the characters.  If @a __pos is
       *  beyond the end of the string, out_of_range is thrown.
      */
      basic_string
      substr(size_type __pos = 0, size_type __n = npos) const
      { return basic_string(*this,
                _M_check(__pos, "basic_string::substr"), __n); }

      /**
       *  @brief  Compare to a string.
       *  @param __str  String to compare against.
       *  @return  Integer < 0, 0, or > 0.
       *
       *  Returns an integer < 0 if this string is ordered before @a
       *  __str, 0 if their values are equivalent, or > 0 if this
       *  string is ordered after @a __str.  Determines the effective
       *  length rlen of the strings to compare as the smallest of
       *  size() and str.size().  The function then compares the two
       *  strings by calling traits::compare(data(), str.data(),rlen).
       *  If the result of the comparison is nonzero returns it,
       *  otherwise the shorter one is ordered first.
      */
      int
      compare(const basic_string& __str) const
      {
    const size_type __size = this->size();
    const size_type __osize = __str.size();
    const size_type __len = std::min(__size, __osize);

    int __r = traits_type::compare(_M_data(), __str.data(), __len);
    if (!__r)
      __r = _S_compare(__size, __osize);
    return __r;
      }

      /**
       *  @brief  Compare substring to a string.
       *  @param __pos  Index of first character of substring.
       *  @param __n  Number of characters in substring.
       *  @param __str  String to compare against.
       *  @return  Integer < 0, 0, or > 0.
       *
       *  Form the substring of this string from the @a __n characters
       *  starting at @a __pos.  Returns an integer < 0 if the
       *  substring is ordered before @a __str, 0 if their values are
       *  equivalent, or > 0 if the substring is ordered after @a
       *  __str.  Determines the effective length rlen of the strings
       *  to compare as the smallest of the length of the substring
       *  and @a __str.size().  The function then compares the two
       *  strings by calling
       *  traits::compare(substring.data(),str.data(),rlen).  If the
       *  result of the comparison is nonzero returns it, otherwise
       *  the shorter one is ordered first.
      */
      int
      compare(size_type __pos, size_type __n, const basic_string& __str) const;

      /**
       *  @brief  Compare substring to a substring.
       *  @param __pos1  Index of first character of substring.
       *  @param __n1  Number of characters in substring.
       *  @param __str  String to compare against.
       *  @param __pos2  Index of first character of substring of str.
       *  @param __n2  Number of characters in substring of str.
       *  @return  Integer < 0, 0, or > 0.
       *
       *  Form the substring of this string from the @a __n1
       *  characters starting at @a __pos1.  Form the substring of @a
       *  __str from the @a __n2 characters starting at @a __pos2.
       *  Returns an integer < 0 if this substring is ordered before
       *  the substring of @a __str, 0 if their values are equivalent,
       *  or > 0 if this substring is ordered after the substring of
       *  @a __str.  Determines the effective length rlen of the
       *  strings to compare as the smallest of the lengths of the
       *  substrings.  The function then compares the two strings by
       *  calling
       *  traits::compare(substring.data(),str.substr(pos2,n2).data(),rlen).
       *  If the result of the comparison is nonzero returns it,
       *  otherwise the shorter one is ordered first.
      */
      int
      compare(size_type __pos1, size_type __n1, const basic_string& __str,
          size_type __pos2, size_type __n2) const;

      /**
       *  @brief  Compare to a C string.
       *  @param __s  C string to compare against.
       *  @return  Integer < 0, 0, or > 0.
       *
       *  Returns an integer < 0 if this string is ordered before @a __s, 0 if
       *  their values are equivalent, or > 0 if this string is ordered after
       *  @a __s.  Determines the effective length rlen of the strings to
       *  compare as the smallest of size() and the length of a string
       *  constructed from @a __s.  The function then compares the two strings
       *  by calling traits::compare(data(),s,rlen).  If the result of the
       *  comparison is nonzero returns it, otherwise the shorter one is
       *  ordered first.
      */
      int
      compare(const _CharT* __s) const;

      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 5 String::compare specification questionable
      /**
       *  @brief  Compare substring to a C string.
       *  @param __pos  Index of first character of substring.
       *  @param __n1  Number of characters in substring.
       *  @param __s  C string to compare against.
       *  @return  Integer < 0, 0, or > 0.
       *
       *  Form the substring of this string from the @a __n1
       *  characters starting at @a pos.  Returns an integer < 0 if
       *  the substring is ordered before @a __s, 0 if their values
       *  are equivalent, or > 0 if the substring is ordered after @a
       *  __s.  Determines the effective length rlen of the strings to
       *  compare as the smallest of the length of the substring and
       *  the length of a string constructed from @a __s.  The
       *  function then compares the two string by calling
       *  traits::compare(substring.data(),__s,rlen).  If the result of
       *  the comparison is nonzero returns it, otherwise the shorter
       *  one is ordered first.
      */
      int
      compare(size_type __pos, size_type __n1, const _CharT* __s) const;

      /**
       *  @brief  Compare substring against a character %array.
       *  @param __pos  Index of first character of substring.
       *  @param __n1  Number of characters in substring.
       *  @param __s  character %array to compare against.
       *  @param __n2  Number of characters of s.
       *  @return  Integer < 0, 0, or > 0.
       *
       *  Form the substring of this string from the @a __n1
       *  characters starting at @a __pos.  Form a string from the
       *  first @a __n2 characters of @a __s.  Returns an integer < 0
       *  if this substring is ordered before the string from @a __s,
       *  0 if their values are equivalent, or > 0 if this substring
       *  is ordered after the string from @a __s.  Determines the
       *  effective length rlen of the strings to compare as the
       *  smallest of the length of the substring and @a __n2.  The
       *  function then compares the two strings by calling
       *  traits::compare(substring.data(),s,rlen).  If the result of
       *  the comparison is nonzero returns it, otherwise the shorter
       *  one is ordered first.
       *
       *  NB: s must have at least n2 characters, &apos;\\0&apos; has
       *  no special meaning.
      */
      int
      compare(size_type __pos, size_type __n1, const _CharT* __s,
          size_type __n2) const;
  };

  // operator+
  /**
   *  @brief  Concatenate two strings.
   *  @param __lhs  First string.
   *  @param __rhs  Last string.
   *  @return  New string with value of @a __lhs followed by @a __rhs.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    basic_string<_CharT, _Traits, _Alloc>
    operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
          const basic_string<_CharT, _Traits, _Alloc>& __rhs)
    {
      basic_string<_CharT, _Traits, _Alloc> __str(__lhs);
      __str.append(__rhs);
      return __str;
    }

  /**
   *  @brief  Concatenate C string and string.
   *  @param __lhs  First string.
   *  @param __rhs  Last string.
   *  @return  New string with value of @a __lhs followed by @a __rhs.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    basic_string<_CharT,_Traits,_Alloc>
    operator+(const _CharT* __lhs,
          const basic_string<_CharT,_Traits,_Alloc>& __rhs);

  /**
   *  @brief  Concatenate character and string.
   *  @param __lhs  First string.
   *  @param __rhs  Last string.
   *  @return  New string with @a __lhs followed by @a __rhs.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    basic_string<_CharT,_Traits,_Alloc>
    operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Alloc>& __rhs);

  /**
   *  @brief  Concatenate string and C string.
   *  @param __lhs  First string.
   *  @param __rhs  Last string.
   *  @return  New string with @a __lhs followed by @a __rhs.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline basic_string<_CharT, _Traits, _Alloc>
    operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
         const _CharT* __rhs)
    {
      basic_string<_CharT, _Traits, _Alloc> __str(__lhs);
      __str.append(__rhs);
      return __str;
    }

  /**
   *  @brief  Concatenate string and character.
   *  @param __lhs  First string.
   *  @param __rhs  Last string.
   *  @return  New string with @a __lhs followed by @a __rhs.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline basic_string<_CharT, _Traits, _Alloc>
    operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, _CharT __rhs)
    {
      typedef basic_string<_CharT, _Traits, _Alloc> __string_type;
      typedef typename __string_type::size_type     __size_type;
      __string_type __str(__lhs);
      __str.append(__size_type(1), __rhs);
      return __str;
    }

#if __cplusplus >= 201103L
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline basic_string<_CharT, _Traits, _Alloc>
    operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
          const basic_string<_CharT, _Traits, _Alloc>& __rhs)
    { return std::move(__lhs.append(__rhs)); }

  template<typename _CharT, typename _Traits, typename _Alloc>
    inline basic_string<_CharT, _Traits, _Alloc>
    operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
          basic_string<_CharT, _Traits, _Alloc>&& __rhs)
    { return std::move(__rhs.insert(0, __lhs)); }

  template<typename _CharT, typename _Traits, typename _Alloc>
    inline basic_string<_CharT, _Traits, _Alloc>
    operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
          basic_string<_CharT, _Traits, _Alloc>&& __rhs)
    {
      const auto __size = __lhs.size() + __rhs.size();
      const bool __cond = (__size > __lhs.capacity()
               && __size <= __rhs.capacity());
      return __cond ? std::move(__rhs.insert(0, __lhs))
                : std::move(__lhs.append(__rhs));
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    inline basic_string<_CharT, _Traits, _Alloc>
    operator+(const _CharT* __lhs,
          basic_string<_CharT, _Traits, _Alloc>&& __rhs)
    { return std::move(__rhs.insert(0, __lhs)); }

  template<typename _CharT, typename _Traits, typename _Alloc>
    inline basic_string<_CharT, _Traits, _Alloc>
    operator+(_CharT __lhs,
          basic_string<_CharT, _Traits, _Alloc>&& __rhs)
    { return std::move(__rhs.insert(0, 1, __lhs)); }

  template<typename _CharT, typename _Traits, typename _Alloc>
    inline basic_string<_CharT, _Traits, _Alloc>
    operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
          const _CharT* __rhs)
    { return std::move(__lhs.append(__rhs)); }

  template<typename _CharT, typename _Traits, typename _Alloc>
    inline basic_string<_CharT, _Traits, _Alloc>
    operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
          _CharT __rhs)
    { return std::move(__lhs.append(1, __rhs)); }
#endif

  // operator ==
  /**
   *  @brief  Test equivalence of two strings.
   *  @param __lhs  First string.
   *  @param __rhs  Second string.
   *  @return  True if @a __lhs.compare(@a __rhs) == 0.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
           const basic_string<_CharT, _Traits, _Alloc>& __rhs)
    { return __lhs.compare(__rhs) == 0; }

  template<typename _CharT>
    inline
    typename __gnu_cxx::__enable_if<__is_char<_CharT>::__value, bool>::__type
    operator==(const basic_string<_CharT>& __lhs,
           const basic_string<_CharT>& __rhs)
    { return (__lhs.size() == __rhs.size()
          && !std::char_traits<_CharT>::compare(__lhs.data(), __rhs.data(),
                            __lhs.size())); }

  /**
   *  @brief  Test equivalence of C string and string.
   *  @param __lhs  C string.
   *  @param __rhs  String.
   *  @return  True if @a __rhs.compare(@a __lhs) == 0.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator==(const _CharT* __lhs,
           const basic_string<_CharT, _Traits, _Alloc>& __rhs)
    { return __rhs.compare(__lhs) == 0; }

  /**
   *  @brief  Test equivalence of string and C string.
   *  @param __lhs  String.
   *  @param __rhs  C string.
   *  @return  True if @a __lhs.compare(@a __rhs) == 0.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator==(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
           const _CharT* __rhs)
    { return __lhs.compare(__rhs) == 0; }

  // operator !=
  /**
   *  @brief  Test difference of two strings.
   *  @param __lhs  First string.
   *  @param __rhs  Second string.
   *  @return  True if @a __lhs.compare(@a __rhs) != 0.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator!=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
           const basic_string<_CharT, _Traits, _Alloc>& __rhs)
    { return !(__lhs == __rhs); }

  /**
   *  @brief  Test difference of C string and string.
   *  @param __lhs  C string.
   *  @param __rhs  String.
   *  @return  True if @a __rhs.compare(@a __lhs) != 0.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator!=(const _CharT* __lhs,
           const basic_string<_CharT, _Traits, _Alloc>& __rhs)
    { return !(__lhs == __rhs); }

  /**
   *  @brief  Test difference of string and C string.
   *  @param __lhs  String.
   *  @param __rhs  C string.
   *  @return  True if @a __lhs.compare(@a __rhs) != 0.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator!=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
           const _CharT* __rhs)
    { return !(__lhs == __rhs); }

  // operator <
  /**
   *  @brief  Test if string precedes string.
   *  @param __lhs  First string.
   *  @param __rhs  Second string.
   *  @return  True if @a __lhs precedes @a __rhs.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
          const basic_string<_CharT, _Traits, _Alloc>& __rhs)
    { return __lhs.compare(__rhs) < 0; }

  /**
   *  @brief  Test if string precedes C string.
   *  @param __lhs  String.
   *  @param __rhs  C string.
   *  @return  True if @a __lhs precedes @a __rhs.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
          const _CharT* __rhs)
    { return __lhs.compare(__rhs) < 0; }

  /**
   *  @brief  Test if C string precedes string.
   *  @param __lhs  C string.
   *  @param __rhs  String.
   *  @return  True if @a __lhs precedes @a __rhs.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator<(const _CharT* __lhs,
          const basic_string<_CharT, _Traits, _Alloc>& __rhs)
    { return __rhs.compare(__lhs) > 0; }

  // operator >
  /**
   *  @brief  Test if string follows string.
   *  @param __lhs  First string.
   *  @param __rhs  Second string.
   *  @return  True if @a __lhs follows @a __rhs.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator>(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
          const basic_string<_CharT, _Traits, _Alloc>& __rhs)
    { return __lhs.compare(__rhs) > 0; }

  /**
   *  @brief  Test if string follows C string.
   *  @param __lhs  String.
   *  @param __rhs  C string.
   *  @return  True if @a __lhs follows @a __rhs.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator>(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
          const _CharT* __rhs)
    { return __lhs.compare(__rhs) > 0; }

  /**
   *  @brief  Test if C string follows string.
   *  @param __lhs  C string.
   *  @param __rhs  String.
   *  @return  True if @a __lhs follows @a __rhs.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator>(const _CharT* __lhs,
          const basic_string<_CharT, _Traits, _Alloc>& __rhs)
    { return __rhs.compare(__lhs) < 0; }

  // operator <=
  /**
   *  @brief  Test if string doesn't follow string.
   *  @param __lhs  First string.
   *  @param __rhs  Second string.
   *  @return  True if @a __lhs doesn't follow @a __rhs.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator<=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
           const basic_string<_CharT, _Traits, _Alloc>& __rhs)
    { return __lhs.compare(__rhs) <= 0; }

  /**
   *  @brief  Test if string doesn't follow C string.
   *  @param __lhs  String.
   *  @param __rhs  C string.
   *  @return  True if @a __lhs doesn't follow @a __rhs.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator<=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
           const _CharT* __rhs)
    { return __lhs.compare(__rhs) <= 0; }

  /**
   *  @brief  Test if C string doesn't follow string.
   *  @param __lhs  C string.
   *  @param __rhs  String.
   *  @return  True if @a __lhs doesn't follow @a __rhs.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator<=(const _CharT* __lhs,
           const basic_string<_CharT, _Traits, _Alloc>& __rhs)
    { return __rhs.compare(__lhs) >= 0; }

  // operator >=
  /**
   *  @brief  Test if string doesn't precede string.
   *  @param __lhs  First string.
   *  @param __rhs  Second string.
   *  @return  True if @a __lhs doesn't precede @a __rhs.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator>=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
           const basic_string<_CharT, _Traits, _Alloc>& __rhs)
    { return __lhs.compare(__rhs) >= 0; }

  /**
   *  @brief  Test if string doesn't precede C string.
   *  @param __lhs  String.
   *  @param __rhs  C string.
   *  @return  True if @a __lhs doesn't precede @a __rhs.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator>=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
           const _CharT* __rhs)
    { return __lhs.compare(__rhs) >= 0; }

  /**
   *  @brief  Test if C string doesn't precede string.
   *  @param __lhs  C string.
   *  @param __rhs  String.
   *  @return  True if @a __lhs doesn't precede @a __rhs.  False otherwise.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline bool
    operator>=(const _CharT* __lhs,
         const basic_string<_CharT, _Traits, _Alloc>& __rhs)
    { return __rhs.compare(__lhs) <= 0; }

  /**
   *  @brief  Swap contents of two strings.
   *  @param __lhs  First string.
   *  @param __rhs  Second string.
   *
   *  Exchanges the contents of @a __lhs and @a __rhs in constant time.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline void
    swap(basic_string<_CharT, _Traits, _Alloc>& __lhs,
     basic_string<_CharT, _Traits, _Alloc>& __rhs)
    { __lhs.swap(__rhs); }

  /**
   *  @brief  Read stream into a string.
   *  @param __is  Input stream.
   *  @param __str  Buffer to store into.
   *  @return  Reference to the input stream.
   *
   *  Stores characters from @a __is into @a __str until whitespace is
   *  found, the end of the stream is encountered, or str.max_size()
   *  is reached.  If is.width() is non-zero, that is the limit on the
   *  number of characters stored into @a __str.  Any previous
   *  contents of @a __str are erased.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    basic_istream<_CharT, _Traits>&
    operator>>(basic_istream<_CharT, _Traits>& __is,
           basic_string<_CharT, _Traits, _Alloc>& __str);

  template<>
    basic_istream<char>&
    operator>>(basic_istream<char>& __is, basic_string<char>& __str);

  /**
   *  @brief  Write string to a stream.
   *  @param __os  Output stream.
   *  @param __str  String to write out.
   *  @return  Reference to the output stream.
   *
   *  Output characters of @a __str into os following the same rules as for
   *  writing a C string.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline basic_ostream<_CharT, _Traits>&
    operator<<(basic_ostream<_CharT, _Traits>& __os,
           const basic_string<_CharT, _Traits, _Alloc>& __str)
    {
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 586. string inserter not a formatted function
      return __ostream_insert(__os, __str.data(), __str.size());
    }

  /**
   *  @brief  Read a line from stream into a string.
   *  @param __is  Input stream.
   *  @param __str  Buffer to store into.
   *  @param __delim  Character marking end of line.
   *  @return  Reference to the input stream.
   *
   *  Stores characters from @a __is into @a __str until @a __delim is
   *  found, the end of the stream is encountered, or str.max_size()
   *  is reached.  Any previous contents of @a __str are erased.  If
   *  @a __delim is encountered, it is extracted but not stored into
   *  @a __str.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    basic_istream<_CharT, _Traits>&
    getline(basic_istream<_CharT, _Traits>& __is,
        basic_string<_CharT, _Traits, _Alloc>& __str, _CharT __delim);

  /**
   *  @brief  Read a line from stream into a string.
   *  @param __is  Input stream.
   *  @param __str  Buffer to store into.
   *  @return  Reference to the input stream.
   *
   *  Stores characters from is into @a __str until &apos;\n&apos; is
   *  found, the end of the stream is encountered, or str.max_size()
   *  is reached.  Any previous contents of @a __str are erased.  If
   *  end of line is encountered, it is extracted but not stored into
   *  @a __str.
   */
  template<typename _CharT, typename _Traits, typename _Alloc>
    inline basic_istream<_CharT, _Traits>&
    getline(basic_istream<_CharT, _Traits>& __is,
        basic_string<_CharT, _Traits, _Alloc>& __str)
    { return getline(__is, __str, __is.widen('\n')); }

  template<>
    basic_istream<char>&
    getline(basic_istream<char>& __in, basic_string<char>& __str,
        char __delim);

#ifdef _GLIBCXX_USE_WCHAR_T
  template<>
    basic_istream<wchar_t>&
    getline(basic_istream<wchar_t>& __in, basic_string<wchar_t>& __str,
        wchar_t __delim);
#endif  

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#if ((__cplusplus >= 201103L) && defined(_GLIBCXX_USE_C99) \
     && !defined(_GLIBCXX_HAVE_BROKEN_VSWPRINTF))

#include <ext/string_conversions.h>

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  // 21.4 Numeric Conversions [string.conversions].
  inline int
  stoi(const string& __str, size_t* __idx = 0, int __base = 10)
  { return __gnu_cxx::__stoa<long, int>(&std::strtol, "stoi", __str.c_str(),
                    __idx, __base); }

  inline long
  stol(const string& __str, size_t* __idx = 0, int __base = 10)
  { return __gnu_cxx::__stoa(&std::strtol, "stol", __str.c_str(),
                 __idx, __base); }

  inline unsigned long
  stoul(const string& __str, size_t* __idx = 0, int __base = 10)
  { return __gnu_cxx::__stoa(&std::strtoul, "stoul", __str.c_str(),
                 __idx, __base); }

  inline long long
  stoll(const string& __str, size_t* __idx = 0, int __base = 10)
  { return __gnu_cxx::__stoa(&std::strtoll, "stoll", __str.c_str(),
                 __idx, __base); }

  inline unsigned long long
  stoull(const string& __str, size_t* __idx = 0, int __base = 10)
  { return __gnu_cxx::__stoa(&std::strtoull, "stoull", __str.c_str(),
                 __idx, __base); }

  // NB: strtof vs strtod.
  inline float
  stof(const string& __str, size_t* __idx = 0)
  { return __gnu_cxx::__stoa(&std::strtof, "stof", __str.c_str(), __idx); }

  inline double
  stod(const string& __str, size_t* __idx = 0)
  { return __gnu_cxx::__stoa(&std::strtod, "stod", __str.c_str(), __idx); }

  inline long double
  stold(const string& __str, size_t* __idx = 0)
  { return __gnu_cxx::__stoa(&std::strtold, "stold", __str.c_str(), __idx); }

  // NB: (v)snprintf vs sprintf.

  // DR 1261.
  inline string
  to_string(int __val)
  { return __gnu_cxx::__to_xstring<string>(&std::vsnprintf, 4 * sizeof(int),
                       "%d", __val); }

  inline string
  to_string(unsigned __val)
  { return __gnu_cxx::__to_xstring<string>(&std::vsnprintf,
                       4 * sizeof(unsigned),
                       "%u", __val); }

  inline string
  to_string(long __val)
  { return __gnu_cxx::__to_xstring<string>(&std::vsnprintf, 4 * sizeof(long),
                       "%ld", __val); }

  inline string
  to_string(unsigned long __val)
  { return __gnu_cxx::__to_xstring<string>(&std::vsnprintf,
                       4 * sizeof(unsigned long),
                       "%lu", __val); }

  inline string
  to_string(long long __val)
  { return __gnu_cxx::__to_xstring<string>(&std::vsnprintf,
                       4 * sizeof(long long),
                       "%lld", __val); }

  inline string
  to_string(unsigned long long __val)
  { return __gnu_cxx::__to_xstring<string>(&std::vsnprintf,
                       4 * sizeof(unsigned long long),
                       "%llu", __val); }

  inline string
  to_string(float __val)
  {
    const int __n = 
      __gnu_cxx::__numeric_traits<float>::__max_exponent10 + 20;
    return __gnu_cxx::__to_xstring<string>(&std::vsnprintf, __n,
                       "%f", __val);
  }

  inline string
  to_string(double __val)
  {
    const int __n = 
      __gnu_cxx::__numeric_traits<double>::__max_exponent10 + 20;
    return __gnu_cxx::__to_xstring<string>(&std::vsnprintf, __n,
                       "%f", __val);
  }

  inline string
  to_string(long double __val)
  {
    const int __n = 
      __gnu_cxx::__numeric_traits<long double>::__max_exponent10 + 20;
    return __gnu_cxx::__to_xstring<string>(&std::vsnprintf, __n,
                       "%Lf", __val);
  }

#ifdef _GLIBCXX_USE_WCHAR_T
  inline int 
  stoi(const wstring& __str, size_t* __idx = 0, int __base = 10)
  { return __gnu_cxx::__stoa<long, int>(&std::wcstol, "stoi", __str.c_str(),
                    __idx, __base); }

  inline long 
  stol(const wstring& __str, size_t* __idx = 0, int __base = 10)
  { return __gnu_cxx::__stoa(&std::wcstol, "stol", __str.c_str(),
                 __idx, __base); }

  inline unsigned long
  stoul(const wstring& __str, size_t* __idx = 0, int __base = 10)
  { return __gnu_cxx::__stoa(&std::wcstoul, "stoul", __str.c_str(),
                 __idx, __base); }

  inline long long
  stoll(const wstring& __str, size_t* __idx = 0, int __base = 10)
  { return __gnu_cxx::__stoa(&std::wcstoll, "stoll", __str.c_str(),
                 __idx, __base); }

  inline unsigned long long
  stoull(const wstring& __str, size_t* __idx = 0, int __base = 10)
  { return __gnu_cxx::__stoa(&std::wcstoull, "stoull", __str.c_str(),
                 __idx, __base); }

  // NB: wcstof vs wcstod.
  inline float
  stof(const wstring& __str, size_t* __idx = 0)
  { return __gnu_cxx::__stoa(&std::wcstof, "stof", __str.c_str(), __idx); }

  inline double
  stod(const wstring& __str, size_t* __idx = 0)
  { return __gnu_cxx::__stoa(&std::wcstod, "stod", __str.c_str(), __idx); }

  inline long double
  stold(const wstring& __str, size_t* __idx = 0)
  { return __gnu_cxx::__stoa(&std::wcstold, "stold", __str.c_str(), __idx); }

  // DR 1261.
  inline wstring
  to_wstring(int __val)
  { return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf, 4 * sizeof(int),
                        L"%d", __val); }

  inline wstring
  to_wstring(unsigned __val)
  { return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf,
                        4 * sizeof(unsigned),
                        L"%u", __val); }

  inline wstring
  to_wstring(long __val)
  { return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf, 4 * sizeof(long),
                        L"%ld", __val); }

  inline wstring
  to_wstring(unsigned long __val)
  { return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf,
                        4 * sizeof(unsigned long),
                        L"%lu", __val); }

  inline wstring
  to_wstring(long long __val)
  { return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf,
                        4 * sizeof(long long),
                        L"%lld", __val); }

  inline wstring
  to_wstring(unsigned long long __val)
  { return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf,
                        4 * sizeof(unsigned long long),
                        L"%llu", __val); }

  inline wstring
  to_wstring(float __val)
  {
    const int __n =
      __gnu_cxx::__numeric_traits<float>::__max_exponent10 + 20;
    return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf, __n,
                        L"%f", __val);
  }

  inline wstring
  to_wstring(double __val)
  {
    const int __n =
      __gnu_cxx::__numeric_traits<double>::__max_exponent10 + 20;
    return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf, __n,
                        L"%f", __val);
  }

  inline wstring
  to_wstring(long double __val)
  {
    const int __n =
      __gnu_cxx::__numeric_traits<long double>::__max_exponent10 + 20;
    return __gnu_cxx::__to_xstring<wstring>(&std::vswprintf, __n,
                        L"%Lf", __val);
  }
#endif

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif /* C++11 && _GLIBCXX_USE_C99 ... */

#if __cplusplus >= 201103L

#include <bits/functional_hash.h>

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  // DR 1182.

#ifndef _GLIBCXX_COMPATIBILITY_CXX0X
  /// std::hash specialization for string.
  template<>
    struct hash<string>
    : public __hash_base<size_t, string>
    {
      size_t
      operator()(const string& __s) const noexcept
      { return std::_Hash_impl::hash(__s.data(), __s.length()); }
    };

  template<>
    struct __is_fast_hash<hash<string>> : std::false_type
    { };

#ifdef _GLIBCXX_USE_WCHAR_T
  /// std::hash specialization for wstring.
  template<>
    struct hash<wstring>
    : public __hash_base<size_t, wstring>
    {
      size_t
      operator()(const wstring& __s) const noexcept
      { return std::_Hash_impl::hash(__s.data(),
                                     __s.length() * sizeof(wchar_t)); }
    };

  template<>
    struct __is_fast_hash<hash<wstring>> : std::false_type
    { };
#endif
#endif /* _GLIBCXX_COMPATIBILITY_CXX0X */

#ifdef _GLIBCXX_USE_C99_STDINT_TR1
  /// std::hash specialization for u16string.
  template<>
    struct hash<u16string>
    : public __hash_base<size_t, u16string>
    {
      size_t
      operator()(const u16string& __s) const noexcept
      { return std::_Hash_impl::hash(__s.data(),
                                     __s.length() * sizeof(char16_t)); }
    };

  template<>
    struct __is_fast_hash<hash<u16string>> : std::false_type
    { };

  /// std::hash specialization for u32string.
  template<>
    struct hash<u32string>
    : public __hash_base<size_t, u32string>
    {
      size_t
      operator()(const u32string& __s) const noexcept
      { return std::_Hash_impl::hash(__s.data(),
                                     __s.length() * sizeof(char32_t)); }
    };

  template<>
    struct __is_fast_hash<hash<u32string>> : std::false_type
    { };
#endif

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif // C++11

#endif /* _BASIC_STRING_H */