// Functions used by iterators -*- C++ -*-
// Copyright (C) 2001-2025 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
// .
/*
*
* Copyright (c) 1994
* Hewlett-Packard Company
*
* Permission to use, copy, modify, distribute and sell this software
* and its documentation for any purpose is hereby granted without fee,
* provided that the above copyright notice appear in all copies and
* that both that copyright notice and this permission notice appear
* in supporting documentation. Hewlett-Packard Company makes no
* representations about the suitability of this software for any
* purpose. It is provided "as is" without express or implied warranty.
*
*
* Copyright (c) 1996-1998
* Silicon Graphics Computer Systems, Inc.
*
* Permission to use, copy, modify, distribute and sell this software
* and its documentation for any purpose is hereby granted without fee,
* provided that the above copyright notice appear in all copies and
* that both that copyright notice and this permission notice appear
* in supporting documentation. Silicon Graphics makes no
* representations about the suitability of this software for any
* purpose. It is provided "as is" without express or implied warranty.
*/
/** @file bits/stl_iterator_base_funcs.h
* This is an internal header file, included by other library headers.
* Do not attempt to use it directly. @headername{iterator}
*
* This file contains all of the general iterator-related utility
* functions, such as distance() and advance().
*/
#ifndef _STL_ITERATOR_BASE_FUNCS_H
#define _STL_ITERATOR_BASE_FUNCS_H 1
#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif
#include
#include
#include
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
_GLIBCXX_BEGIN_NAMESPACE_CONTAINER
// Forward declaration for the overloads of __distance.
template struct _List_iterator;
template struct _List_const_iterator;
_GLIBCXX_END_NAMESPACE_CONTAINER
template
inline _GLIBCXX14_CONSTEXPR
typename iterator_traits<_InputIterator>::difference_type
__distance(_InputIterator __first, _InputIterator __last,
input_iterator_tag)
{
// concept requirements
__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
typename iterator_traits<_InputIterator>::difference_type __n = 0;
while (__first != __last)
{
++__first;
++__n;
}
return __n;
}
template
__attribute__((__always_inline__))
inline _GLIBCXX14_CONSTEXPR
typename iterator_traits<_RandomAccessIterator>::difference_type
__distance(_RandomAccessIterator __first, _RandomAccessIterator __last,
random_access_iterator_tag)
{
// concept requirements
__glibcxx_function_requires(_RandomAccessIteratorConcept<
_RandomAccessIterator>)
return __last - __first;
}
#if _GLIBCXX_USE_CXX11_ABI
// Forward declaration because of the qualified call in distance.
template
ptrdiff_t
__distance(_GLIBCXX_STD_C::_List_iterator<_Tp>,
_GLIBCXX_STD_C::_List_iterator<_Tp>,
input_iterator_tag);
template
ptrdiff_t
__distance(_GLIBCXX_STD_C::_List_const_iterator<_Tp>,
_GLIBCXX_STD_C::_List_const_iterator<_Tp>,
input_iterator_tag);
#endif
#if __cplusplus >= 201103L
// Give better error if std::distance called with a non-Cpp17InputIterator.
template
void
__distance(_OutputIterator, _OutputIterator, output_iterator_tag) = delete;
#endif
#ifdef __glibcxx_concepts
namespace __detail
{
// Satisfied if ITER_TRAITS(Iter)::iterator_category is valid and is
// at least as strong as ITER_TRAITS(Iter)::iterator_concept.
template
concept __iter_category_converts_to_concept
= convertible_to::iterator_category,
typename __iter_traits<_Iter>::iterator_concept>;
// Satisfied if the type is a C++20 iterator that defines iterator_concept,
// and its iterator_concept is stronger than its iterator_category (if any).
// Used by std::distance and std::advance to detect iterators which should
// dispatch based on their C++20 concept not their C++17 category.
template
concept __promotable_iterator
= input_iterator<_Iter>
&& requires { typename __iter_traits<_Iter>::iterator_concept; }
&& ! __iter_category_converts_to_concept<_Iter>;
} // namespace __detail
#endif
/**
* @brief A generalization of pointer arithmetic.
* @param __first An input iterator.
* @param __last An input iterator.
* @return The distance between them.
*
* Returns @c n such that __first + n == __last. This requires
* that @p __last must be reachable from @p __first. Note that @c
* n may be negative.
*
* For random access iterators, this uses their @c + and @c - operations
* and are constant time. For other %iterator classes they are linear time.
*/
template
_GLIBCXX_NODISCARD __attribute__((__always_inline__))
inline _GLIBCXX17_CONSTEXPR
typename iterator_traits<_InputIterator>::difference_type
distance(_InputIterator __first, _InputIterator __last)
{
#ifdef __glibcxx_concepts
// A type which satisfies the C++20 random_access_iterator concept might
// have input_iterator_tag as its iterator_category type, which would
// mean we select the O(n) __distance. Or a C++20 std::input_iterator
// that is not a Cpp17InputIterator might have output_iterator_tag as
// its iterator_category type and then calling __distance with
// std::__iterator_category(__first) would be ill-formed.
// So for C++20 iterator types we can just choose to do the right thing.
if constexpr (__detail::__promotable_iterator<_InputIterator>)
{
if constexpr (random_access_iterator<_InputIterator>)
return __last - __first;
else
return std::__distance(std::move(__first), std::move(__last),
input_iterator_tag());
}
else // assume it meets the Cpp17InputIterator requirements:
#endif
// concept requirements -- taken care of in __distance
return std::__distance(__first, __last,
std::__iterator_category(__first));
}
template
inline _GLIBCXX14_CONSTEXPR void
__advance(_InputIterator& __i, _Distance __n, input_iterator_tag)
{
// concept requirements
__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
__glibcxx_assert(__n >= 0);
while (__n-- > 0)
++__i;
}
template
inline _GLIBCXX14_CONSTEXPR void
__advance(_BidirectionalIterator& __i, _Distance __n,
bidirectional_iterator_tag)
{
// concept requirements
__glibcxx_function_requires(_BidirectionalIteratorConcept<
_BidirectionalIterator>)
if (__n > 0)
while (__n--)
++__i;
else
while (__n++)
--__i;
}
template
inline _GLIBCXX14_CONSTEXPR void
__advance(_RandomAccessIterator& __i, _Distance __n,
random_access_iterator_tag)
{
// concept requirements
__glibcxx_function_requires(_RandomAccessIteratorConcept<
_RandomAccessIterator>)
if (__builtin_constant_p(__n) && __n == 1)
++__i;
else if (__builtin_constant_p(__n) && __n == -1)
--__i;
else
__i += __n;
}
#if __cplusplus >= 201103L
// Give better error if std::advance called with a non-Cpp17InputIterator.
template
void
__advance(_OutputIterator&, _Distance, output_iterator_tag) = delete;
#endif
/**
* @brief A generalization of pointer arithmetic.
* @param __i An input iterator.
* @param __n The @a delta by which to change @p __i.
* @return Nothing.
*
* This increments @p i by @p n. For bidirectional and random access
* iterators, @p __n may be negative, in which case @p __i is decremented.
*
* For random access iterators, this uses their @c + and @c - operations
* and are constant time. For other %iterator classes they are linear time.
*/
template
__attribute__((__always_inline__))
inline _GLIBCXX17_CONSTEXPR void
advance(_InputIterator& __i, _Distance __n)
{
#ifdef __glibcxx_concepts
// A type which satisfies the C++20 bidirectional_iterator concept might
// have input_iterator_tag as its iterator_category type, which would
// mean we select the __advance overload which cannot move backwards.
// For a C++20 random_access_iterator we might select the O(n) __advance
// if it doesn't meet the Cpp17RandomAccessIterator requirements.
// So for C++20 iterator types we can just choose to do the right thing.
if constexpr (__detail::__promotable_iterator<_InputIterator>
&& ranges::__detail::__is_integer_like<_Distance>)
{
auto __d = static_cast>(__n);
if constexpr (random_access_iterator<_InputIterator>)
std::__advance(__i, __d, random_access_iterator_tag());
else if constexpr (bidirectional_iterator<_InputIterator>)
std::__advance(__i, __d, bidirectional_iterator_tag());
else
std::__advance(__i, __d, input_iterator_tag());
}
else // assume it meets the Cpp17InputIterator requirements:
#endif
{
// concept requirements -- taken care of in __advance
typename iterator_traits<_InputIterator>::difference_type __d = __n;
std::__advance(__i, __d, std::__iterator_category(__i));
}
}
#if __cplusplus >= 201103L
template
_GLIBCXX_NODISCARD [[__gnu__::__always_inline__]]
inline _GLIBCXX17_CONSTEXPR _InputIterator
next(_InputIterator __x, typename
iterator_traits<_InputIterator>::difference_type __n = 1)
{
// concept requirements
__glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
std::advance(__x, __n);
return __x;
}
template
_GLIBCXX_NODISCARD [[__gnu__::__always_inline__]]
inline _GLIBCXX17_CONSTEXPR _BidirectionalIterator
prev(_BidirectionalIterator __x, typename
iterator_traits<_BidirectionalIterator>::difference_type __n = 1)
{
// concept requirements
__glibcxx_function_requires(_BidirectionalIteratorConcept<
_BidirectionalIterator>)
std::advance(__x, -__n);
return __x;
}
#endif // C++11
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif /* _STL_ITERATOR_BASE_FUNCS_H */