std::ranges::find_last, std::ranges::find_last_if, std::ranges::find_last_if_not

 

C++

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Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Algorithm library

Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
is_execution_policy (C++17)   execution::seqexecution::parexecution::par_unseqexecution::unseq (C++17)    (C++17)(C++17)(C++20)	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced (C++17)(C++17)(C++17)(C++20)
Non-modifying sequence operations Batch operations for_each for_each_n (C++17) Search operations all_ofany_ofnone_of (C++11)                (C++11)(C++11) countcount_if mismatch equal findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n Modifying sequence operations Copy operations copycopy_if (C++11) copy_backward copy_n (C++11) move (C++11) move_backward (C++11) Swap operations swap iter_swap swap_ranges Transformation operations replacereplace_if transform replace_copyreplace_copy_if Generation operations fill fill_n generate generate_n Removing operations removeremove_if unique remove_copyremove_copy_if unique_copy Order-changing operations reverse reverse_copy rotate rotate_copy random_shuffleshuffle (until C++17)(C++11) shift_leftshift_right (C++20)(C++20) Sampling operations sample (C++17)	Sorting and related operations Partitioning operations partition partition_copy (C++11)   stable_partition is_partitioned (C++11) partition_point (C++11) Sorting operations sort stable_sort partial_sort partial_sort_copy is_sorted (C++11) is_sorted_until (C++11) nth_element Binary search operations (on partitioned ranges) lower_bound upper_bound equal_range binary_search Set operations (on sorted ranges) includes set_union set_intersection set_difference set_symmetric_difference Merge operations (on sorted ranges) merge inplace_merge Heap operations push_heap pop_heap make_heap sort_heap is_heap (C++11) is_heap_until (C++11) Minimum/maximum operations max min minmax (C++11) clamp (C++17) max_element min_element minmax_element (C++11) Lexicographical comparison operations lexicographical_compare lexicographical_compare_three_way (C++20) Permutation operations next_permutation prev_permutation is_permutation (C++11) C library qsort bsearch
Numeric operations
iota (C++11) inner_product adjacent_difference    accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17)    exclusive_scan (C++17) transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
Operations on uninitialized memory
uninitialized_copy uninitialized_move (C++17)    uninitialized_fill uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	destroy (C++17) destroy_n (C++17) destroy_at (C++17) construct_at (C++20)       uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17)

 

Constrained algorithms

All names in this menu belong to namespace std::ranges

Non-modifying sequence operations

all_ofany_ofnone_of for_each for_each_n    countcount_if adjacent_find mismatch equal lexicographical_compare    containscontains_subrange (C++23)(C++23) findfind_iffind_if_not find_lastfind_last_iffind_last_if_not (C++23)(C++23)(C++23)   find_end find_first_of search search_n starts_with (C++23) ends_with (C++23)

Modifying sequence operations

copycopy_if copy_n copy_backward    move move_backward shift_leftshift_right (C++23)(C++23)   fill fill_n generate generate_n    transform swap_ranges    shuffle sample removeremove_if replacereplace_if reverse rotate remove_copyremove_copy_if    unique replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy

Partitioning operations

is_partitioned    partition_point    partition    partition_copy    stable_partition

Sorting operations

is_sorted is_sorted_until     sort stable_sort         partial_sort       nth_element partial_sort_copy

Binary search operations (on sorted ranges)

lower_bound         upper_bound         binary_search      equal_range

Set operations (on sorted ranges)

merge inplace_merge       set_difference set_intersection    set_union          includes set_symmetric_difference

Heap operations

is_heap is_heap_until       make_heap           sort_heap push_heap pop_heap

Minimum/maximum operations

max max_element         min min_element         minmax minmax_element     clamp

Permutation operations

is_permutation      next_permutation    prev_permutation

Fold operations

fold_left (C++23) fold_left_first (C++23)   fold_right (C++23) fold_right_last (C++23)   fold_left_with_iter (C++23) fold_left_first_with_iter (C++23)

Numeric operations iota (C++23)             Random number generation generate_random (C++26)

Operations on uninitialized storage

construct_at    destroy destroy_n destroy_at uninitialized_copy    uninitialized_move uninitialized_fill uninitialized_copy_n    uninitialized_move_n uninitialized_fill_n uninitialized_default_construct uninitialized_default_construct_n uninitialized_value_construct uninitialized_value_construct_n

Return types

in_fun_result in_in_result in_found_result    in_out_result in_in_out_result    in_out_out_result    min_max_result out_value_result (C++23) in_value_result (C++23)

 

Defined in header <algorithm>
Call signature
template< std::forward_iterator I, std::sentinel_for<I> S,           class T, class Proj = std::identity > requires std::indirect_binary_predicate<ranges::equal_to, std::projected<I, Proj>,                                         const T*> constexpr ranges::subrange<I>     find_last( I first, S last, const T& value, Proj proj = {} );	(1)	(since C++23)
template< ranges::forward_range R, class T, class Proj = std::identity > requires std::indirect_binary_predicate<ranges::equal_to,                                         std::projected<ranges::iterator_t<R>, Proj>,                                         const T*> constexpr ranges::borrowed_subrange_t<R>     find_last( R&& r, const T& value, Proj proj = {} );	(2)	(since C++23)
template< std::forward_iterator I, std::sentinel_for<I> S,           class Proj = std::identity,           std::indirect_unary_predicate<std::projected<I, Proj>> Pred > constexpr ranges::subrange<I>     find_last_if( I first, S last, Pred pred, Proj proj = {} );	(3)	(since C++23)
template< ranges::forward_range R, class Proj = std::identity,           std::indirect_unary_predicate<std::projected<ranges::iterator_t<R>, Proj>>               Pred > constexpr ranges::borrowed_subrange_t<R>     find_last_if( R&& r, Pred pred, Proj proj = {} );	(4)	(since C++23)
template< std::forward_iterator I, std::sentinel_for<I> S,           class Proj = std::identity,           std::indirect_unary_predicate<std::projected<I, Proj>> Pred > constexpr ranges::subrange<I>     find_last_if_not( I first, S last, Pred pred, Proj proj = {} );	(5)	(since C++23)
template< ranges::forward_range R, class Proj = std::identity,           std::indirect_unary_predicate<std::projected<ranges::iterator_t<R>, Proj>>               Pred > constexpr ranges::borrowed_subrange_t<R>     find_last_if_not( R&& r, Pred pred, Proj proj = {} );	(6)	(since C++23)

Returns the last element in the range [first, last) that satisfies specific criteria:

1) find_last searches for an element equal to value

3) find_last_if searches for the last element in the range [first, last) for which predicate pred returns true

5) find_last_if_not searches for the last element in the range [first, last) for which predicate pred returns false

2,4,6) Same as (1,3,5), but uses r as the source range, as if using ranges::begin(r) as first and ranges::end(r) as last.

The function-like entities described on this page are niebloids, that is:

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible to argument-dependent lookup.
• When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

In practice, they may be implemented as function objects, or with special compiler extensions.

Parameters

first, last	-	the range of elements to examine
r	-	the range of the elements to examine
value	-	value to compare the elements to
pred	-	predicate to apply to the projected elements
proj	-	projection to apply to the elements

Return value

1,2,3) Let i be the last iterator in the range [first,last) for which E is true. Returns ranges::subrange<I>{i, last}, or ranges::subrange<I>{last, last} if no such iterator is found.

2,4,6) Same as (1,2,3) but the return type is ranges::borrowed_subrange_t<I>.

Complexity

At most last - first applications of the predicate and projection.

Notes

ranges::find_last, ranges::find_last_if, ranges::find_last_if_not have better efficiency on common implementations if I models bidirectional_iterator or (better) random_access_iterator.

Feature-test macro	Value	Std	Feature
__cpp_lib_find_last	202207L	(C++23)	ranges::find_last, ranges::find_last_if, ranges::find_last_if_not

Possible implementation

These implementations only show the slower algorithm used when I models forward_iterator.

find_last
struct find_last_fn { template< std::forward_iterator I, std::sentinel_for<I> S, class T, class Proj = std::identity > requires std::indirect_binary_predicate<ranges::equal_to, std::projected<I, Proj>, const T*> constexpr ranges::subrange<I> operator()(I first, S last, const T &value, Proj proj = {}) const { // Note: if I is mere forward_iterator, we may only go from begin to end. I found{}; for (; first != last; ++first) if (std::invoke(proj, *first) == value) found = first;   if (found == I{}) return {first, first};   return {found, std::ranges::next(found, last)}; }   template< ranges::forward_range R, class T, class Proj = std::identity > requires std::indirect_binary_predicate<ranges::equal_to, std::projected<ranges::iterator_t<R>, Proj>, const T*> constexpr ranges::borrowed_subrange_t<R> operator()(R&& r, const T &value, Proj proj = {}) const { return this->operator()(ranges::begin(r), ranges::end(r), value, std::ref(proj)); } };   inline constexpr find_last_fn find_last;
find_last_if
struct find_last_if_fn { template< std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_unary_predicate<std::projected<I, Proj>> Pred > constexpr ranges::subrange<I> operator()(I first, S last, Pred pred, Proj proj = {}) const { // Note: if I is mere forward_iterator, we may only go from begin to end. I found{}; for (; first != last; ++first) if (std::invoke(pred, std::invoke(proj, *first))) found = first;   if (found == I{}) return {first, first};   return {found, std::ranges::next(found, last)}; }   template< ranges::forward_range R, class Proj = std::identity, std::indirect_unary_predicate<std::projected<ranges::iterator_t<R>, Proj>> Pred > constexpr ranges::borrowed_subrange_t<R> operator()(R&& r, Pred pred, Proj proj = {}) const { return this->operator()(ranges::begin(r), ranges::end(r), std::ref(pred), std::ref(proj)); } };   inline constexpr find_last_if_fn find_last_if;
find_last_if_not
struct find_last_if_not_fn { template< std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_unary_predicate<std::projected<I, Proj>> Pred > constexpr ranges::subrange<I> operator()(I first, S last, Pred pred, Proj proj = {}) const { // Note: if I is mere forward_iterator, we may only go from begin to end. I found{}; for (; first != last; ++first) if (!std::invoke(pred, std::invoke(proj, *first))) found = first;   if (found == I{}) return {first, first};   return {found, std::ranges::next(found, last)}; }   template< ranges::forward_range R, class Proj = std::identity, std::indirect_unary_predicate<std::projected<ranges::iterator_t<R>, Proj>> Pred > constexpr ranges::borrowed_subrange_t<R> operator()(R&& r, Pred pred, Proj proj = {}) const { return this->operator()(ranges::begin(r), ranges::end(r), std::ref(pred), std::ref(proj)); } };   inline constexpr find_last_if_not_fn find_last_if_not;

Example

A link to test: Compiler Explorer/g++-trunk

Run this code

#include <algorithm>
#include <forward_list>
#include <iomanip>
#include <iostream>
#include <string_view>
 
int main()
{
    constexpr static auto v = {1, 2, 3, 1, 2, 3, 1, 2};
 
    {
        constexpr auto i1 = std::ranges::find_last(v.begin(), v.end(), 3);
        constexpr auto i2 = std::ranges::find_last(v, 3);
        static_assert(std::ranges::distance(v.begin(), i1.begin()) == 5);
        static_assert(std::ranges::distance(v.begin(), i2.begin()) == 5);
    }
    {
        constexpr auto i1 = std::ranges::find_last(v.begin(), v.end(), -3);
        constexpr auto i2 = std::ranges::find_last(v, -3);
        static_assert(i1.begin() == v.end());
        static_assert(i2.begin() == v.end());
    }
 
    auto abs = [](int x) { return x < 0 ? -x : x; };
 
    {
        auto pred = [](int x) { return x == 3; };
        constexpr auto i1 = std::ranges::find_last_if(v.begin(), v.end(), pred, abs);
        constexpr auto i2 = std::ranges::find_last_if(v, pred, abs);
        static_assert(std::ranges::distance(v.begin(), i1.begin()) == 5);
        static_assert(std::ranges::distance(v.begin(), i2.begin()) == 5);
    }
    {
        auto pred = [](int x) { return x == -3; };
        constexpr auto i1 = std::ranges::find_last_if(v.begin(), v.end(), pred, abs);
        constexpr auto i2 = std::ranges::find_last_if(v, pred, abs);
        static_assert(i1.begin() == v.end());
        static_assert(i2.begin() == v.end());
    }
 
    {
        auto pred = [](int x) { return x == 1 or x == 2; };
        constexpr auto i1 = std::ranges::find_last_if_not(v.begin(), v.end(), pred, abs);
        constexpr auto i2 = std::ranges::find_last_if_not(v, pred, abs);
        static_assert(std::ranges::distance(v.begin(), i1.begin()) == 5);
        static_assert(std::ranges::distance(v.begin(), i2.begin()) == 5);
    }
    {
        auto pred = [](int x) { return x == 1 or x == 2 or x == 3; };
        constexpr auto i1 = std::ranges::find_last_if_not(v.begin(), v.end(), pred, abs);
        constexpr auto i2 = std::ranges::find_last_if_not(v, pred, abs);
        static_assert(i1.begin() == v.end());
        static_assert(i2.begin() == v.end());
    }
 
    using P = std::pair<std::string_view, int>;
    std::forward_list<P> list
    {
        {"one", 1}, {"two", 2}, {"three", 3},
        {"one", 4}, {"two", 5}, {"three", 6},
    };
    auto cmp_one = [](const std::string_view &s) { return s == "one"; };
 
    // find latest element that satisfy the comparator, and projecting pair::first
    const auto subrange = std::ranges::find_last_if(list, cmp_one, &P::first);
 
    // print the found element and the "tail" after it
    for (P const& e : subrange)
        std::cout << '{' << std::quoted(e.first) << ", " << e.second << "} ";
    std::cout << '\n';
}

Output:

{"one", 4} {"two", 5} {"three", 6}

See also

ranges::find_end (C++20)	finds the last sequence of elements in a certain range (niebloid)
ranges::findranges::find_ifranges::find_if_not (C++20)(C++20)(C++20)	finds the first element satisfying specific criteria (niebloid)
ranges::search (C++20)	searches for the first occurrence of a range of elements (niebloid)
ranges::includes (C++20)	returns true if one sequence is a subsequence of another (niebloid)
ranges::binary_search (C++20)	determines if an element exists in a partially-ordered range (niebloid)
ranges::containsranges::contains_subrange (C++23)(C++23)	checks if the range contains the given element or subrange (niebloid)