basic_string.tcc

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

// Copyright (C) 1997-2026 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.tcc
 *  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
//

// Written by Jason Merrill based upon the specification by Takanori Adachi
// in ANSI X3J16/94-0013R2.  Rewritten by Nathan Myers to ISO-14882.
// Non-reference-counted implementation written by Paolo Carlini and
// updated by Jonathan Wakely for ISO-14882-2011.

#ifndef _BASIC_STRING_TCC
#define _BASIC_STRING_TCC 1

#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wc++11-extensions"

#include <bits/cxxabi_forced.h>

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

#if _GLIBCXX_USE_CXX11_ABI

  template<typename _CharT, typename _Traits, typename _Alloc>
    const typename basic_string<_CharT, _Traits, _Alloc>::size_type
    basic_string<_CharT, _Traits, _Alloc>::npos;

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX20_CONSTEXPR
    void
    basic_string<_CharT, _Traits, _Alloc>::
    swap(basic_string& __s) _GLIBCXX_NOEXCEPT
    {
      if (this == std::__addressof(__s))
        return;

      _Alloc_traits::_S_on_swap(_M_get_allocator(), __s._M_get_allocator());

      if (_M_is_local())
        if (__s._M_is_local())
          {
            if (length() && __s.length())
              {
                _CharT __tmp_data[_S_local_capacity + 1];
                traits_type::copy(__tmp_data, __s._M_local_buf,
                                  __s.length() + 1);
                traits_type::copy(__s._M_local_buf, _M_local_buf,
                                  length() + 1);
                traits_type::copy(_M_local_buf, __tmp_data,
                                  __s.length() + 1);
              }
            else if (__s.length())
              {
                _M_init_local_buf();
                traits_type::copy(_M_local_buf, __s._M_local_buf,
                                  __s.length() + 1);
                _M_length(__s.length());
                __s._M_set_length(0);
                return;
              }
            else if (length())
              {
                __s._M_init_local_buf();
                traits_type::copy(__s._M_local_buf, _M_local_buf,
                                  length() + 1);
                __s._M_length(length());
                _M_set_length(0);
                return;
              }
          }
        else
          {
            const size_type __tmp_capacity = __s._M_allocated_capacity;
            __s._M_init_local_buf();
            traits_type::copy(__s._M_local_buf, _M_local_buf,
                              length() + 1);
            _M_data(__s._M_data());
            __s._M_data(__s._M_local_buf);
            _M_capacity(__tmp_capacity);
          }
      else
        {
          const size_type __tmp_capacity = _M_allocated_capacity;
          if (__s._M_is_local())
            {
              _M_init_local_buf();
              traits_type::copy(_M_local_buf, __s._M_local_buf,
                                __s.length() + 1);
              __s._M_data(_M_data());
              _M_data(_M_local_buf);
            }
          else
            {
              pointer __tmp_ptr = _M_data();
              _M_data(__s._M_data());
              __s._M_data(__tmp_ptr);
              _M_capacity(__s._M_allocated_capacity);
            }
          __s._M_capacity(__tmp_capacity);
        }

      const size_type __tmp_length = length();
      _M_length(__s.length());
      __s._M_length(__tmp_length);
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX20_CONSTEXPR
    typename basic_string<_CharT, _Traits, _Alloc>::pointer
    basic_string<_CharT, _Traits, _Alloc>::
    _M_create(size_type& __capacity, size_type __old_capacity)
    {
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 83.  String::npos vs. string::max_size()
      if (__capacity > max_size())
        std::__throw_length_error(__N("basic_string::_M_create"));

      // The below implements an exponential growth policy, necessary to
      // meet amortized linear time requirements of the library: see
      // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
      if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)
        {
          __capacity = 2 * __old_capacity;
          // Never allocate a string bigger than max_size.
          if (__capacity > max_size())
            __capacity = max_size();
        }

      // NB: Need an array of char_type[__capacity], plus a terminating
      // null char_type() element.
      return _S_allocate(_M_get_allocator(), __capacity + 1);
    }

  // NB: This is the special case for Input Iterators, used in
  // istreambuf_iterators, etc.
  // Input Iterators have a cost structure very different from
  // pointers, calling for a different coding style.
  template<typename _CharT, typename _Traits, typename _Alloc>
    template<typename _InIterator>
      _GLIBCXX20_CONSTEXPR
      void
      basic_string<_CharT, _Traits, _Alloc>::
      _M_construct(_InIterator __beg, _InIterator __end,
                   std::input_iterator_tag)
      {
        size_type __len = 0;
        size_type __capacity = size_type(_S_local_capacity);

        _M_init_local_buf();

        while (__beg != __end && __len < __capacity)
          {
            _M_local_buf[__len++] = *__beg;
            ++__beg;
          }

        struct _Guard
        {
          _GLIBCXX20_CONSTEXPR
          explicit _Guard(basic_string* __s) : _M_guarded(__s) { }

          _GLIBCXX20_CONSTEXPR
          ~_Guard() { if (_M_guarded) _M_guarded->_M_dispose(); }

          basic_string* _M_guarded;
        } __guard(this);

        while (__beg != __end)
          {
            if (__len == __capacity)
              {
                // Allocate more space.
                __capacity = __len + 1;
                pointer __another = _M_create(__capacity, __len);
                this->_S_copy(__another, _M_data(), __len);
                _M_dispose();
                _M_data(__another);
                _M_capacity(__capacity);
              }
            traits_type::assign(_M_data()[__len++],
                                static_cast<_CharT>(*__beg));
            ++__beg;
          }

        __guard._M_guarded = 0;

        _M_set_length(__len);
      }

  template<typename _CharT, typename _Traits, typename _Alloc>
    template<typename _InIterator>
      _GLIBCXX20_CONSTEXPR
      void
      basic_string<_CharT, _Traits, _Alloc>::
      _M_construct(_InIterator __beg, _InIterator __end,
                   std::forward_iterator_tag)
      {
        size_type __dnew = static_cast<size_type>(std::distance(__beg, __end));

        if (__dnew > size_type(_S_local_capacity))
          {
            _M_data(_M_create(__dnew, size_type(0)));
            _M_capacity(__dnew);
          }
        else
          _M_init_local_buf();

        // Check for out_of_range and length_error exceptions.
        struct _Guard
        {
          _GLIBCXX20_CONSTEXPR
          explicit _Guard(basic_string* __s) : _M_guarded(__s) { }

          _GLIBCXX20_CONSTEXPR
          ~_Guard() { if (_M_guarded) _M_guarded->_M_dispose(); }

          basic_string* _M_guarded;
        } __guard(this);

        this->_S_copy_chars(_M_data(), __beg, __end);

        __guard._M_guarded = 0;

        _M_set_length(__dnew);
      }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX20_CONSTEXPR
    void
    basic_string<_CharT, _Traits, _Alloc>::
    _M_construct(size_type __n, _CharT __c)
    {
      if (__n > size_type(_S_local_capacity))
        {
          _M_data(_M_create(__n, size_type(0)));
          _M_capacity(__n);
        }
      else
        _M_init_local_buf();

      if (__n)
        this->_S_assign(_M_data(), __n, __c);

      _M_set_length(__n);
    }

  // Length of string constructed is easier to propagate inter-procedurally
  // than difference between iterators.
  template<typename _CharT, typename _Traits, typename _Alloc>
    template<bool _Terminated>
    _GLIBCXX20_CONSTEXPR 
    void
    basic_string<_CharT, _Traits, _Alloc>::
    _M_construct(const _CharT* __str, size_type __n)
    {
      if (__n > size_type(_S_local_capacity))
        {
          _M_data(_M_create(__n, size_type(0)));
          _M_capacity(__n);
        }
      else
        _M_init_local_buf();

      if (__n || _Terminated)
        this->_S_copy(_M_data(), __str, __n + _Terminated);

      _M_length(__n);
      if (!_Terminated)
        traits_type::assign(_M_data()[__n], _CharT());
    }

#if __cplusplus >= 202302L
  template<typename _CharT, typename _Traits, typename _Alloc>
    constexpr void
    basic_string<_CharT, _Traits, _Alloc>::
    _M_construct(basic_string&& __str, size_type __pos,  size_type __n)
    {
      const _CharT* __start = __str._M_data() + __pos;
      if (__n <= _S_local_capacity)
        {
          _M_init_local_buf();
          traits_type::copy(_M_local_buf, __start, __n);
          _M_set_length(__n);
          return;
        }

      if constexpr (!allocator_traits<_Alloc>::is_always_equal::value)
        if (get_allocator() != __str.get_allocator())
          {
            _M_construct<false>(__start, __n);
            return;
          }

      _M_data(__str._M_data());
      _M_capacity(__str._M_allocated_capacity);
      __str._M_data(__str._M_use_local_data());
      __str._M_set_length(0);

      _S_move(_M_data(), _M_data() + __pos, __n);
      _M_set_length(__n);
    }
#endif // C++23

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX20_CONSTEXPR
    void
    basic_string<_CharT, _Traits, _Alloc>::
    _M_assign(const basic_string& __str)
    {
      if (this != std::__addressof(__str))
        {
          const size_type __rsize = __str.length();
          const size_type __capacity = capacity();

          if (__rsize > __capacity)
            {
              size_type __new_capacity = __rsize;
              pointer __tmp = _M_create(__new_capacity, __capacity);
              _M_dispose();
              _M_data(__tmp);
              _M_capacity(__new_capacity);
            }

          if (__rsize)
            this->_S_copy(_M_data(), __str._M_data(), __rsize);

          _M_set_length(__rsize);
        }
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX20_CONSTEXPR
    void
    basic_string<_CharT, _Traits, _Alloc>::
    reserve(size_type __res)
    {
      const size_type __capacity = capacity();
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 2968. Inconsistencies between basic_string reserve and
      // vector/unordered_map/unordered_set reserve functions
      // P0966 reserve should not shrink
      if (__res <= __capacity)
        return;

      pointer __tmp = _M_create(__res, __capacity);
      this->_S_copy(__tmp, _M_data(), length() + 1);
      _M_dispose();
      _M_data(__tmp);
      _M_capacity(__res);
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX20_CONSTEXPR
    void
    basic_string<_CharT, _Traits, _Alloc>::
    _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
              size_type __len2)
    {
      const size_type __how_much = length() - __pos - __len1;

      size_type __new_capacity = length() + __len2 - __len1;
      pointer __r = _M_create(__new_capacity, capacity());

      if (__pos)
        this->_S_copy(__r, _M_data(), __pos);
      if (__s && __len2)
        this->_S_copy(__r + __pos, __s, __len2);
      if (__how_much)
        this->_S_copy(__r + __pos + __len2,
                      _M_data() + __pos + __len1, __how_much);

      _M_dispose();
      _M_data(__r);
      _M_capacity(__new_capacity);
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX20_CONSTEXPR
    void
    basic_string<_CharT, _Traits, _Alloc>::
    _M_erase(size_type __pos, size_type __n)
    {
      const size_type __how_much = length() - __pos - __n;

      if (__how_much && __n)
        this->_S_move(_M_data() + __pos, _M_data() + __pos + __n, __how_much);

      _M_set_length(length() - __n);
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX20_CONSTEXPR
    void
    basic_string<_CharT, _Traits, _Alloc>::
    reserve()
    {
      if (_M_is_local())
        return;

      const size_type __length = length();
      const size_type __capacity = _M_allocated_capacity;

      if (__length <= size_type(_S_local_capacity))
        {
          _M_init_local_buf();
          this->_S_copy(_M_local_buf, _M_data(), __length + 1);
          _M_destroy(__capacity);
          _M_data(_M_local_data());
        }
#if __cpp_exceptions
      else if (__length < __capacity)
        try
          {
            pointer __tmp = _S_allocate(_M_get_allocator(), __length + 1);
            this->_S_copy(__tmp, _M_data(), __length + 1);
            _M_dispose();
            _M_data(__tmp);
            _M_capacity(__length);
          }
        catch (const __cxxabiv1::__forced_unwind&)
          { throw; }
        catch (...)
          { /* swallow the exception */ }
#endif
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX20_CONSTEXPR
    void
    basic_string<_CharT, _Traits, _Alloc>::
    resize(size_type __n, _CharT __c)
    {
      const size_type __size = this->size();
      if (__size < __n)
        this->append(__n - __size, __c);
      else if (__n < __size)
        this->_M_set_length(__n);
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX20_CONSTEXPR
    basic_string<_CharT, _Traits, _Alloc>&
    basic_string<_CharT, _Traits, _Alloc>::
    _M_append(const _CharT* __s, size_type __n)
    {
      const size_type __len = __n + this->size();

      if (__len <= this->capacity())
        {
          if (__n)
            this->_S_copy(this->_M_data() + this->size(), __s, __n);
        }
      else
        this->_M_mutate(this->size(), size_type(0), __s, __n);

      this->_M_set_length(__len);
      return *this;
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    template<typename _InputIterator>
      _GLIBCXX20_CONSTEXPR
      basic_string<_CharT, _Traits, _Alloc>&
      basic_string<_CharT, _Traits, _Alloc>::
      _M_replace_dispatch(const_iterator __i1, const_iterator __i2,
                          _InputIterator __k1, _InputIterator __k2,
                          std::__false_type)
      {
        // _GLIBCXX_RESOLVE_LIB_DEFECTS
        // 2788. unintentionally require a default constructible allocator
        const basic_string __s(__k1, __k2, this->get_allocator());
        const size_type __n1 = __i2 - __i1;
        return _M_replace(__i1 - begin(), __n1, __s._M_data(),
                          __s.size());
      }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX20_CONSTEXPR
    basic_string<_CharT, _Traits, _Alloc>&
    basic_string<_CharT, _Traits, _Alloc>::
    _M_replace_aux(size_type __pos1, size_type __n1, size_type __n2,
                   _CharT __c)
    {
      _M_check_length(__n1, __n2, "basic_string::_M_replace_aux");

      const size_type __old_size = this->size();
      const size_type __new_size = __old_size + __n2 - __n1;

      if (__new_size <= this->capacity())
        {
          pointer __p = this->_M_data() + __pos1;

          const size_type __how_much = __old_size - __pos1 - __n1;
          if (__how_much && __n1 != __n2)
            this->_S_move(__p + __n2, __p + __n1, __how_much);
        }
      else
        this->_M_mutate(__pos1, __n1, 0, __n2);

      if (__n2)
        this->_S_assign(this->_M_data() + __pos1, __n2, __c);

      this->_M_set_length(__new_size);
      return *this;
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    __attribute__((__noinline__, __noclone__, __cold__)) void
    basic_string<_CharT, _Traits, _Alloc>::
    _M_replace_cold(pointer __p, size_type __len1, const _CharT* __s,
                    const size_type __len2, const size_type __how_much)
    {
      // Work in-place.
      if (__len2 && __len2 <= __len1)
        this->_S_move(__p, __s, __len2);
      if (__how_much && __len1 != __len2)
        this->_S_move(__p + __len2, __p + __len1, __how_much);
      if (__len2 > __len1)
        {
          if (__s + __len2 <= __p + __len1)
            this->_S_move(__p, __s, __len2);
          else if (__s >= __p + __len1)
            {
              // Hint to middle end that __p and __s overlap
              // (PR 98465).
              const size_type __poff = (__s - __p) + (__len2 - __len1);
              this->_S_copy(__p, __p + __poff, __len2);
            }
          else
            {
              const size_type __nleft = (__p + __len1) - __s;
              this->_S_move(__p, __s, __nleft);
              this->_S_copy(__p + __nleft, __p + __len2, __len2 - __nleft);
            }
        }
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX20_CONSTEXPR
    basic_string<_CharT, _Traits, _Alloc>&
    basic_string<_CharT, _Traits, _Alloc>::
    _M_replace(size_type __pos, size_type __len1, const _CharT* __s,
               const size_type __len2)
    {
      _M_check_length(__len1, __len2, "basic_string::_M_replace");

      const size_type __old_size = this->size();
      const size_type __new_size = __old_size + __len2 - __len1;

      if (__new_size <= this->capacity())
        {
          pointer __p = this->_M_data() + __pos;

          const size_type __how_much = __old_size - __pos - __len1;
#if __cpp_lib_is_constant_evaluated
          if (std::is_constant_evaluated())
            {
              auto __newp = _S_allocate(_M_get_allocator(), __new_size);
              _S_copy(__newp, this->_M_data(), __pos);
              _S_copy(__newp + __pos, __s, __len2);
              _S_copy(__newp + __pos + __len2, __p + __len1, __how_much);
              _S_copy(this->_M_data(), __newp, __new_size);
              this->_M_get_allocator().deallocate(__newp, __new_size);
            }
          else
#endif
          if (__builtin_expect(_M_disjunct(__s), true))
            {
              if (__how_much && __len1 != __len2)
                this->_S_move(__p + __len2, __p + __len1, __how_much);
              if (__len2)
                this->_S_copy(__p, __s, __len2);
            }
          else
            _M_replace_cold(__p, __len1, __s, __len2, __how_much);
        }
      else
        this->_M_mutate(__pos, __len1, __s, __len2);

      this->_M_set_length(__new_size);
      return *this;
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX20_CONSTEXPR
    typename basic_string<_CharT, _Traits, _Alloc>::size_type
    basic_string<_CharT, _Traits, _Alloc>::
    copy(_CharT* __s, size_type __n, size_type __pos) const
    {
      _M_check(__pos, "basic_string::copy");
      __n = _M_limit(__pos, __n);
      __glibcxx_requires_string_len(__s, __n);
      if (__n)
        _S_copy(__s, _M_data() + __pos, __n);
      // 21.3.5.7 par 3: do not append null.  (good.)
      return __n;
    }

#ifdef __glibcxx_string_resize_and_overwrite // C++ >= 23
  template<typename _CharT, typename _Traits, typename _Alloc>
  template<typename _Operation>
    [[__gnu__::__always_inline__]]
    constexpr void
    basic_string<_CharT, _Traits, _Alloc>::
    __resize_and_overwrite(const size_type __n, _Operation __op)
    { resize_and_overwrite<_Operation&>(__n, __op); }
#endif

#if __cplusplus >= 201103L
  template<typename _CharT, typename _Traits, typename _Alloc>
  template<typename _Operation>
    _GLIBCXX20_CONSTEXPR void
    basic_string<_CharT, _Traits, _Alloc>::
#ifdef __glibcxx_string_resize_and_overwrite // C++ >= 23
    resize_and_overwrite(const size_type __n, _Operation __op)
#else
    __resize_and_overwrite(const size_type __n, _Operation __op)
#endif
    {
      reserve(__n);
      _CharT* const __p = _M_data();
#if __cpp_lib_is_constant_evaluated
      if (std::__is_constant_evaluated() && __n > size())
        traits_type::assign(__p + size(), __n - size(), _CharT());
#endif
      struct _Terminator {
        _GLIBCXX20_CONSTEXPR ~_Terminator() { _M_this->_M_set_length(_M_r); }
        basic_string* _M_this;
        size_type _M_r;
      };
      _Terminator __term{this, 0};
      auto __r = std::move(__op)(__p + 0, __n + 0);
#ifdef __cpp_lib_concepts
      static_assert(ranges::__detail::__is_integer_like<decltype(__r)>);
#else
      static_assert(__gnu_cxx::__is_integer_nonstrict<decltype(__r)>::__value,
                    "resize_and_overwrite operation must return an integer");
#endif
      _GLIBCXX_DEBUG_ASSERT(__r >= 0 && size_type(__r) <= __n);
      __term._M_r = size_type(__r);
      if (__term._M_r > __n)
        __builtin_unreachable();
    }
#endif // C++11

#endif  // _GLIBCXX_USE_CXX11_ABI
   
#if __glibcxx_constexpr_string >= 201907L
# define _GLIBCXX_STRING_CONSTEXPR constexpr
#else
# define _GLIBCXX_STRING_CONSTEXPR
#endif
  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX_STRING_CONSTEXPR
    typename basic_string<_CharT, _Traits, _Alloc>::size_type
    basic_string<_CharT, _Traits, _Alloc>::
    find(const _CharT* __s, size_type __pos, size_type __n) const
    _GLIBCXX_NOEXCEPT
    {
      __glibcxx_requires_string_len(__s, __n);
      const size_type __size = this->size();

      if (__n == 0)
        return __pos <= __size ? __pos : npos;
      if (__pos >= __size)
        return npos;

      const _CharT __elem0 = __s[0];
      const _CharT* const __data = data();
      const _CharT* __first = __data + __pos;
      const _CharT* const __last = __data + __size;
      size_type __len = __size - __pos;

      while (__len >= __n)
        {
          // Find the first occurrence of __elem0:
          __first = traits_type::find(__first, __len - __n + 1, __elem0);
          if (!__first)
            return npos;
          // Compare the full strings from the first occurrence of __elem0.
          // We already know that __first[0] == __s[0] but compare them again
          // anyway because __s is probably aligned, which helps memcmp.
          if (traits_type::compare(__first, __s, __n) == 0)
            return __first - __data;
          __len = __last - ++__first;
        }
      return npos;
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX_STRING_CONSTEXPR
    typename basic_string<_CharT, _Traits, _Alloc>::size_type
    basic_string<_CharT, _Traits, _Alloc>::
    find(_CharT __c, size_type __pos) const _GLIBCXX_NOEXCEPT
    {
      size_type __ret = npos;
      const size_type __size = this->size();
      if (__pos < __size)
        {
          const _CharT* __data = _M_data();
          const size_type __n = __size - __pos;
          const _CharT* __p = traits_type::find(__data + __pos, __n, __c);
          if (__p)
            __ret = __p - __data;
        }
      return __ret;
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX_STRING_CONSTEXPR
    typename basic_string<_CharT, _Traits, _Alloc>::size_type
    basic_string<_CharT, _Traits, _Alloc>::
    rfind(const _CharT* __s, size_type __pos, size_type __n) const
    _GLIBCXX_NOEXCEPT
    {
      __glibcxx_requires_string_len(__s, __n);
      const size_type __size = this->size();
      if (__n <= __size)
        {
          __pos = std::min(size_type(__size - __n), __pos);
          const _CharT* __data = _M_data();
          do
            {
              if (traits_type::compare(__data + __pos, __s, __n) == 0)
                return __pos;
            }
          while (__pos-- > 0);
        }
      return npos;
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX_STRING_CONSTEXPR
    typename basic_string<_CharT, _Traits, _Alloc>::size_type
    basic_string<_CharT, _Traits, _Alloc>::
    rfind(_CharT __c, size_type __pos) const _GLIBCXX_NOEXCEPT
    {
      size_type __size = this->size();
      if (__size)
        {
          if (--__size > __pos)
            __size = __pos;
          for (++__size; __size-- > 0; )
            if (traits_type::eq(_M_data()[__size], __c))
              return __size;
        }
      return npos;
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX_STRING_CONSTEXPR
    typename basic_string<_CharT, _Traits, _Alloc>::size_type
    basic_string<_CharT, _Traits, _Alloc>::
    find_first_of(const _CharT* __s, size_type __pos, size_type __n) const
    _GLIBCXX_NOEXCEPT
    {
      __glibcxx_requires_string_len(__s, __n);
      for (; __n && __pos < this->size(); ++__pos)
        {
          const _CharT* __p = traits_type::find(__s, __n, _M_data()[__pos]);
          if (__p)
            return __pos;
        }
      return npos;
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX_STRING_CONSTEXPR
    typename basic_string<_CharT, _Traits, _Alloc>::size_type
    basic_string<_CharT, _Traits, _Alloc>::
    find_last_of(const _CharT* __s, size_type __pos, size_type __n) const
    _GLIBCXX_NOEXCEPT
    {
      __glibcxx_requires_string_len(__s, __n);
      size_type __size = this->size();
      if (__size && __n)
        {
          if (--__size > __pos)
            __size = __pos;
          do
            {
              if (traits_type::find(__s, __n, _M_data()[__size]))
                return __size;
            }
          while (__size-- != 0);
        }
      return npos;
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX_STRING_CONSTEXPR
    typename basic_string<_CharT, _Traits, _Alloc>::size_type
    basic_string<_CharT, _Traits, _Alloc>::
    find_first_not_of(const _CharT* __s, size_type __pos, size_type __n) const
    _GLIBCXX_NOEXCEPT
    {
      __glibcxx_requires_string_len(__s, __n);
      for (; __pos < this->size(); ++__pos)
        if (!traits_type::find(__s, __n, _M_data()[__pos]))
          return __pos;
      return npos;
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX_STRING_CONSTEXPR
    typename basic_string<_CharT, _Traits, _Alloc>::size_type
    basic_string<_CharT, _Traits, _Alloc>::
    find_first_not_of(_CharT __c, size_type __pos) const _GLIBCXX_NOEXCEPT
    {
      for (; __pos < this->size(); ++__pos)
        if (!traits_type::eq(_M_data()[__pos], __c))
          return __pos;
      return npos;
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX_STRING_CONSTEXPR
    typename basic_string<_CharT, _Traits, _Alloc>::size_type
    basic_string<_CharT, _Traits, _Alloc>::
    find_last_not_of(const _CharT* __s, size_type __pos, size_type __n) const
    _GLIBCXX_NOEXCEPT
    {
      __glibcxx_requires_string_len(__s, __n);
      size_type __size = this->size();
      if (__size)
        {
          if (--__size > __pos)
            __size = __pos;
          do
            {
              if (!traits_type::find(__s, __n, _M_data()[__size]))
                return __size;
            }
          while (__size--);
        }
      return npos;
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    _GLIBCXX_STRING_CONSTEXPR
    typename basic_string<_CharT, _Traits, _Alloc>::size_type
    basic_string<_CharT, _Traits, _Alloc>::
    find_last_not_of(_CharT __c, size_type __pos) const _GLIBCXX_NOEXCEPT
    {
      size_type __size = this->size();
      if (__size)
        {
          if (--__size > __pos)
            __size = __pos;
          do
            {
              if (!traits_type::eq(_M_data()[__size], __c))
                return __size;
            }
          while (__size--);
        }
      return npos;
    }

#undef _GLIBCXX_STRING_CONSTEXPR

  // 21.3.7.9 basic_string::getline and operators
  template<typename _CharT, typename _Traits, typename _Alloc>
    basic_istream<_CharT, _Traits>&
    operator>>(basic_istream<_CharT, _Traits>& __in,
               basic_string<_CharT, _Traits, _Alloc>& __str)
    {
      typedef basic_istream<_CharT, _Traits>            __istream_type;
      typedef basic_string<_CharT, _Traits, _Alloc>     __string_type;
      typedef typename __istream_type::ios_base         __ios_base;
      typedef typename __istream_type::int_type         __int_type;
      typedef typename __string_type::size_type         __size_type;
      typedef ctype<_CharT>                             __ctype_type;
      typedef typename __ctype_type::ctype_base         __ctype_base;

      __size_type __extracted = 0;
      typename __ios_base::iostate __err = __ios_base::goodbit;
      typename __istream_type::sentry __cerb(__in, false);
      if (__cerb)
        {
          __try
            {
              // Avoid reallocation for common case.
              __str.erase();
              _CharT __buf[128];
              __size_type __len = 0;          
              const streamsize __w = __in.width();
              const __size_type __n = __w > 0 ? static_cast<__size_type>(__w)
                                              : __str.max_size();
              const __ctype_type& __ct = use_facet<__ctype_type>(__in.getloc());
              const __int_type __eof = _Traits::eof();
              __int_type __c = __in.rdbuf()->sgetc();

              while (__extracted < __n
                     && !_Traits::eq_int_type(__c, __eof)
                     && !__ct.is(__ctype_base::space,
                                 _Traits::to_char_type(__c)))
                {
                  if (__len == sizeof(__buf) / sizeof(_CharT))
                    {
                      __str.append(__buf, sizeof(__buf) / sizeof(_CharT));
                      __len = 0;
                    }
                  __buf[__len++] = _Traits::to_char_type(__c);
                  ++__extracted;
                  __c = __in.rdbuf()->snextc();
                }
              __str.append(__buf, __len);

              if (__extracted < __n && _Traits::eq_int_type(__c, __eof))
                __err |= __ios_base::eofbit;
              __in.width(0);
            }
          __catch(__cxxabiv1::__forced_unwind&)
            {
              __in._M_setstate(__ios_base::badbit);
              __throw_exception_again;
            }
          __catch(...)
            {
              // _GLIBCXX_RESOLVE_LIB_DEFECTS
              // 91. Description of operator>> and getline() for string<>
              // might cause endless loop
              __in._M_setstate(__ios_base::badbit);
            }
        }
      // 211.  operator>>(istream&, string&) doesn't set failbit
      if (!__extracted)
        __err |= __ios_base::failbit;
      if (__err)
        __in.setstate(__err);
      return __in;
    }

  template<typename _CharT, typename _Traits, typename _Alloc>
    basic_istream<_CharT, _Traits>&
    getline(basic_istream<_CharT, _Traits>& __in,
            basic_string<_CharT, _Traits, _Alloc>& __str, _CharT __delim)
    {
      typedef basic_istream<_CharT, _Traits>            __istream_type;
      typedef basic_string<_CharT, _Traits, _Alloc>     __string_type;
      typedef typename __istream_type::ios_base         __ios_base;
      typedef typename __istream_type::int_type         __int_type;
      typedef typename __string_type::size_type         __size_type;

      __size_type __extracted = 0;
      const __size_type __n = __str.max_size();
      typename __ios_base::iostate __err = __ios_base::goodbit;
      typename __istream_type::sentry __cerb(__in, true);
      if (__cerb)
        {
          __try
            {
              __str.erase();
              const __int_type __idelim = _Traits::to_int_type(__delim);
              const __int_type __eof = _Traits::eof();
              __int_type __c = __in.rdbuf()->sgetc();

              while (__extracted < __n
                     && !_Traits::eq_int_type(__c, __eof)
                     && !_Traits::eq_int_type(__c, __idelim))
                {
                  __str += _Traits::to_char_type(__c);
                  ++__extracted;
                  __c = __in.rdbuf()->snextc();
                }

              if (_Traits::eq_int_type(__c, __eof))
                __err |= __ios_base::eofbit;
              else if (_Traits::eq_int_type(__c, __idelim))
                {
                  ++__extracted;                  
                  __in.rdbuf()->sbumpc();
                }
              else
                __err |= __ios_base::failbit;
            }
          __catch(__cxxabiv1::__forced_unwind&)
            {
              __in._M_setstate(__ios_base::badbit);
              __throw_exception_again;
            }
          __catch(...)
            {
              // _GLIBCXX_RESOLVE_LIB_DEFECTS
              // 91. Description of operator>> and getline() for string<>
              // might cause endless loop
              __in._M_setstate(__ios_base::badbit);
            }
        }
      if (!__extracted)
        __err |= __ios_base::failbit;
      if (__err)
        __in.setstate(__err);
      return __in;
    }

  // Inhibit implicit instantiations for required instantiations,
  // which are defined via explicit instantiations elsewhere.
#if _GLIBCXX_EXTERN_TEMPLATE
  // The explicit instantiation definitions in src/c++11/string-inst.cc and
  // src/c++17/string-inst.cc only instantiate the members required for C++17
  // and earlier standards (so not C++20's starts_with and ends_with).
  // Suppress the explicit instantiation declarations for C++20, so C++20
  // code will implicitly instantiate std::string and std::wstring as needed.
# if __cplusplus <= 201703L && _GLIBCXX_EXTERN_TEMPLATE > 0
  extern template class basic_string<char>;
# elif ! _GLIBCXX_USE_CXX11_ABI
  // Still need to prevent implicit instantiation of the COW empty rep,
  // to ensure the definition in libstdc++.so is unique (PR 86138).
  extern template basic_string<char>::size_type
    basic_string<char>::_Rep::_S_empty_rep_storage[];
# elif _GLIBCXX_EXTERN_TEMPLATE > 0
  // Export _M_replace_cold even for C++20.
  extern template void
    basic_string<char>::_M_replace_cold(char *, size_type, const char*,
                                        const size_type, const size_type);
# endif

  extern template
    basic_istream<char>&
    operator>>(basic_istream<char>&, string&);
  extern template
    basic_ostream<char>&
    operator<<(basic_ostream<char>&, const string&);
  extern template
    basic_istream<char>&
    getline(basic_istream<char>&, string&, char);
  extern template
    basic_istream<char>&
    getline(basic_istream<char>&, string&);

#ifdef _GLIBCXX_USE_WCHAR_T
# if __cplusplus <= 201703L && _GLIBCXX_EXTERN_TEMPLATE > 0
  extern template class basic_string<wchar_t>;
# elif ! _GLIBCXX_USE_CXX11_ABI
  extern template basic_string<wchar_t>::size_type
    basic_string<wchar_t>::_Rep::_S_empty_rep_storage[];
# elif _GLIBCXX_EXTERN_TEMPLATE > 0
  // Export _M_replace_cold even for C++20.
  extern template void
    basic_string<wchar_t>::_M_replace_cold(wchar_t*, size_type, const wchar_t*,
                                           const size_type, const size_type);
# endif

  extern template
    basic_istream<wchar_t>&
    operator>>(basic_istream<wchar_t>&, wstring&);
  extern template
    basic_ostream<wchar_t>&
    operator<<(basic_ostream<wchar_t>&, const wstring&);
  extern template
    basic_istream<wchar_t>&
    getline(basic_istream<wchar_t>&, wstring&, wchar_t);
  extern template
    basic_istream<wchar_t>&
    getline(basic_istream<wchar_t>&, wstring&);
#endif // _GLIBCXX_USE_WCHAR_T
#endif // _GLIBCXX_EXTERN_TEMPLATE

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#pragma GCC diagnostic pop
#endif