std::ranges::find, std::ranges::find_if, std::ranges::find_if_not

 

C++

Compiler support

Freestanding and hosted

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
	(1)
template< std::input_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 I find( I first, S last, const T& value, Proj proj = {} );			(since C++20) (until C++26)
template< std::input_iterator I, std::sentinel_for<I> S,           class Proj = std::identity,           class T = std::projected_value_t<I, Proj> > requires std::indirect_binary_predicate              <ranges::equal_to, std::projected<I, Proj>, const T*> constexpr I find( I first, S last, const T& value, Proj proj = {} );			(since C++26)
		(2)
template< ranges::input_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_iterator_t<R>     find( R&& r, const T& value, Proj proj = {} );				(since C++20) (until C++26)
template< ranges::input_range R, class Proj = std::identity,           class T = std::projected_value_t<ranges::iterator_t<R>, Proj> > requires std::indirect_binary_predicate              <ranges::equal_to,               std::projected<ranges::iterator_t<R>, Proj>, const T*> constexpr ranges::borrowed_iterator_t<R>     find( R&& r, const T& value, Proj proj = {} );				(since C++26)
template< std::input_iterator I, std::sentinel_for<I> S,           class Proj = std::identity,           std::indirect_unary_predicate<std::projected<I, Proj>> Pred > constexpr I find_if( I first, S last, Pred pred, Proj proj = {} );			(3)	(since C++20)
template< ranges::input_range R, class Proj = std::identity,           std::indirect_unary_predicate               <std::projected<ranges::iterator_t<R>, Proj>> Pred > constexpr ranges::borrowed_iterator_t<R>     find_if( R&& r, Pred pred, Proj proj = {} );			(4)	(since C++20)
template< std::input_iterator I, std::sentinel_for<I> S,           class Proj = std::identity,           std::indirect_unary_predicate<std::projected<I, Proj>> Pred > constexpr I find_if_not( I first, S last, Pred pred, Proj proj = {} );			(5)	(since C++20)
template< ranges::input_range R, class Proj = std::identity,           std::indirect_unary_predicate               <std::projected<ranges::iterator_t<R>, Proj>> Pred > constexpr ranges::borrowed_iterator_t<R>     find_if_not( R&& r, Pred pred, Proj proj = {} );			(6)	(since C++20)

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

1) find searches for an element equal to value.

3) find_if searches for an element for which predicate pred returns true.

5) find_if_not searches for an element 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

Iterator to the first element satisfying the condition or iterator equal to last if no such element is found.

Complexity

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

Possible implementation

find
struct find_fn { template<std::input_iterator I, std::sentinel_for<I> S, class Proj = std::identity, class T = std::projected_value_t<I, Proj>> requires std::indirect_binary_predicate <ranges::equal_to, std::projected<I, Proj>, const T*> constexpr I operator()(I first, S last, const T& value, Proj proj = {}) const { for (; first != last; ++first) if (std::invoke(proj, *first) == value) return first; return first; }   template<ranges::input_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_iterator_t<R> operator()(R&& r, const T& value, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), value, std::ref(proj)); } };   inline constexpr find_fn find;
find_if
struct find_if_fn { template<std::input_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_unary_predicate<std::projected<I, Proj>> Pred> constexpr I operator()(I first, S last, Pred pred, Proj proj = {}) const { for (; first != last; ++first) if (std::invoke(pred, std::invoke(proj, *first))) return first; return first; }   template<ranges::input_range R, class Proj = std::identity, std::indirect_unary_predicate <std::projected<ranges::iterator_t<R>, Proj>> Pred> constexpr ranges::borrowed_iterator_t<R> operator()(R&& r, Pred pred, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), std::ref(pred), std::ref(proj)); } };   inline constexpr find_if_fn find_if;
find_if_not
struct find_if_not_fn { template<std::input_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_unary_predicate<std::projected<I, Proj>> Pred> constexpr I operator()(I first, S last, Pred pred, Proj proj = {}) const { for (; first != last; ++first) if (!std::invoke(pred, std::invoke(proj, *first))) return first; return first; }   template<ranges::input_range R, class Proj = std::identity, std::indirect_unary_predicate <std::projected<ranges::iterator_t<R>, Proj>> Pred> constexpr ranges::borrowed_iterator_t<R> operator()(R&& r, Pred pred, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), std::ref(pred), std::ref(proj)); } };   inline constexpr find_if_not_fn find_if_not;

Notes

Feature-test macro	Value	Std	Feature
__cpp_lib_algorithm_default_value_type	202403	(C++26)	List-initialization for algorithms (1,2)

Example

Run this code

#include <algorithm>
#include <cassert>
#include <complex>
#include <format>
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
 
void projector_example()
{
    struct folk_info
    {
        unsigned uid;
        std::string name, position;
    };
 
    std::vector<folk_info> folks
    {
        {0, "Ana", "dev"},
        {1, "Bob", "devops"},
        {2, "Eve", "ops"}
    };
 
    const auto who{"Eve"};
    if (auto it = std::ranges::find(folks, who, &folk_info::name); it != folks.end())
        std::cout << std::format("Profile:\n"
                                 "    UID: {}\n"
                                 "    Name: {}\n"
                                 "    Position: {}\n\n",
                                 it->uid, it->name, it->position);
}
 
int main()
{
    namespace ranges = std::ranges;
 
    projector_example();
 
    const int n1 = 3;
    const int n2 = 5;
    const auto v = {4, 1, 3, 2};
 
    if (ranges::find(v, n1) != v.end())
        std::cout << "v contains: " << n1 << '\n';
    else
        std::cout << "v does not contain: " << n1 << '\n';
 
    if (ranges::find(v.begin(), v.end(), n2) != v.end())
        std::cout << "v contains: " << n2 << '\n';
    else
        std::cout << "v does not contain: " << n2 << '\n';
 
    auto is_even = [](int x) { return x % 2 == 0; };
 
    if (auto result = ranges::find_if(v.begin(), v.end(), is_even); result != v.end())
        std::cout << "First even element in v: " << *result << '\n';
    else
        std::cout << "No even elements in v\n";
 
    if (auto result = ranges::find_if_not(v, is_even); result != v.end())
        std::cout << "First odd element in v: " << *result << '\n';
    else
        std::cout << "No odd elements in v\n";
 
    auto divides_13 = [](int x) { return x % 13 == 0; };
 
    if (auto result = ranges::find_if(v, divides_13); result != v.end())
        std::cout << "First element divisible by 13 in v: " << *result << '\n';
    else
        std::cout << "No elements in v are divisible by 13\n";
 
    if (auto result = ranges::find_if_not(v.begin(), v.end(), divides_13);
        result != v.end())
        std::cout << "First element indivisible by 13 in v: " << *result << '\n';
    else
        std::cout << "All elements in v are divisible by 13\n";
 
    std::vector<std::complex<double>> nums{{4, 2}};
    #ifdef __cpp_lib_algorithm_default_value_type
        // T gets deduced in (2) making list-initialization possible
        const auto it = ranges::find(nums, {4, 2});
    #else
        const auto it = ranges::find(nums, std::complex<double>{4, 2});
    #endif
    assert(it == nums.begin());
}

Output:

Profile:
    UID: 2
    Name: Eve
    Position: ops
 
v contains: 3
v does not contain: 5
First even element in v: 4
First odd element in v: 1
No elements in v are divisible by 13
First element indivisible by 13 in v: 4

See also

ranges::adjacent_find (C++20)	finds the first two adjacent items that are equal (or satisfy a given predicate) (niebloid)
ranges::find_end (C++20)	finds the last sequence of elements in a certain range (niebloid)
ranges::find_first_of (C++20)	searches for any one of a set of elements (niebloid)
ranges::mismatch (C++20)	finds the first position where two ranges differ (niebloid)
ranges::search (C++20)	searches for the first occurrence of a range of elements (niebloid)
findfind_iffind_if_not (C++11)	finds the first element satisfying specific criteria (function template)