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

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

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)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Algorithm library

Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms: std::ranges::copy, std::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
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each for_each_n (C++17)	countcount_if mismatch equal adjacent_find	findfind_iffind_if_not (C++11) find_end find_first_of	search search_n lexicographical_compare lexicographical_compare_three_way (C++20)
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) shift_leftshift_right (C++20)(C++20) transform	fill fill_n generate generate_n swap iter_swap swap_ranges sample (C++17)	removeremove_if replacereplace_if reverse rotate unique random_shuffle (until C++17)	remove_copyremove_copy_if replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy shuffle (C++11)
Operations on uninitialized storage
uninitialized_copy uninitialized_move (C++17) uninitialized_fill destroy (C++17)	uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n destroy_n (C++17)	uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) destroy_at (C++17)	uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17) construct_at (C++20)
Partitioning operations
is_partitioned (C++11) partition_point (C++11)	partition partition_copy (C++11)	stable_partition
Sorting operations
is_sorted (C++11) is_sorted_until (C++11)	sort stable_sort	partial_sort partial_sort_copy	nth_element
Binary search operations
lower_bound	upper_bound	binary_search	equal_range
Set operations (on sorted ranges)
merge inplace_merge	set_difference set_intersection	set_symmetric_difference set_union	includes
Heap operations
is_heap (C++11) is_heap_until (C++11)	make_heap sort_heap	push_heap pop_heap
Minimum/maximum operations
max max_element	min min_element	minmax (C++11) minmax_element (C++11)	clamp (C++17)
Permutations
is_permutation (C++11)	next_permutation	prev_permutation
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)
C library
qsort	bsearch

 

Constrained algorithms

Non-modifying sequence operations
ranges::all_ofranges::any_ofranges::none_of ranges::for_each ranges::for_each_n	ranges::countranges::count_if ranges::mismatch ranges::equal	ranges::findranges::find_ifranges::find_if_not ranges::find_end ranges::find_first_of	ranges::adjacent_find ranges::search ranges::search_n ranges::lexicographical_compare
Modifying sequence operations
ranges::copyranges::copy_if ranges::copy_n ranges::copy_backward ranges::move ranges::move_backward ranges::transform	ranges::fill ranges::fill_n ranges::generate ranges::generate_n ranges::swap_ranges ranges::shuffle ranges::sample	ranges::removeranges::remove_if ranges::replaceranges::replace_if ranges::reverse ranges::rotate ranges::unique	ranges::remove_copyranges::remove_copy_if ranges::replace_copyranges::replace_copy_if ranges::reverse_copy ranges::rotate_copy ranges::unique_copy
Operations on uninitialized storage
ranges::uninitialized_copy   ranges::uninitialized_move ranges::uninitialized_fill ranges::destroy	ranges::uninitialized_copy_n   ranges::uninitialized_move_n ranges::uninitialized_fill_n ranges::destroy_n	ranges::uninitialized_default_construct   ranges::uninitialized_value_construct ranges::destroy_at	ranges::uninitialized_default_construct_n ranges::uninitialized_value_construct_n ranges::construct_at
Partitioning operations
ranges::is_partitioned ranges::partition_point	ranges::partition ranges::partition_copy	ranges::stable_partition
Sorting operations
ranges::is_sorted ranges::is_sorted_until	ranges::sort ranges::stable_sort	ranges::partial_sort ranges::partial_sort_copy	ranges::nth_element
Binary search operations
ranges::lower_bound	ranges::upper_bound	ranges::binary_search	ranges::equal_range
Set operations (on sorted ranges)
ranges::merge ranges::inplace_merge	ranges::set_difference ranges::set_intersection	ranges::set_symmetric_difference ranges::set_union	ranges::includes
Heap operations
ranges::is_heap ranges::is_heap_until	ranges::make_heap ranges::sort_heap	ranges::push_heap ranges::pop_heap
Minimum/maximum operations
ranges::max ranges::max_element	ranges::min ranges::min_element	ranges::minmax ranges::minmax_element	ranges::clamp
Permutations
ranges::is_permutation	ranges::next_permutation	ranges::prev_permutation

 

Defined in header <algorithm>
Call signature
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 = {} );	(1)	(since C++20)
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 = {} );	(2)	(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( 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 may not be specified when calling any of them.
• None of them is visible to argument-dependent lookup.
• When one of them is found by normal unqualified lookup for the name to the left of the function-call operator, it inhibits argument-dependent lookup.

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

First version
struct find_fn { 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 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;
Second version
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;
Third version
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;

Example

The following example finds an integer in a vector of integers.

Run this code

#include <iostream>
#include <algorithm>
#include <vector>
#include <iterator>
 
int main()
{
    int n1 = 3;
    int n2 = 5;
 
    std::vector<int> v{4, 1, 3, 2};
 
    namespace ranges = std::ranges;
 
    auto result1 = ranges::find(v, n1);
    auto result2 = ranges::find(v.begin(), v.end(), n2);
 
    if (result1 != v.end()) {
        std::cout << "v contains: " << n1 << '\n';
    } else {
        std::cout << "v does not contain: " << n1 << '\n';
    }
 
    if (result2 != 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; };
    auto divides_13 = [](int x) { return x % 13 == 0; };
 
    auto result3 = ranges::find_if(v.begin(), v.end(), is_even);
    auto result4 = ranges::find_if(v, divides_13);
    if (result3 != v.end()) {
      std::cout << "First even element in v: " << *result3 << '\n';
    } else {
      std::cout << "No even elements in v\n";
    }
 
    if (result4 != v.end()) {
      std::cout << "First element divisible by 13 in v: " << *result4 << '\n';
    } else {
      std::cout << "No elements in v are divisible by 13\n";
    }
 
    auto result5 = ranges::find_if_not(v.begin(), v.end(), divides_13);
    auto result6 = ranges::find_if_not(v, is_even);
    if (result5 != v.end()) {
      std::cout << "First element indivisible by 13 in v: " << *result5 << '\n';
    } else {
      std::cout << "No elements in v are divisible by 13\n";
    }
 
    if (result6 != v.end()) {
      std::cout << "First odd element in v: " << *result6 << '\n';
    } else {
      std::cout << "No even elements in v\n";
    }
}

Output:

v contains: 3
v does not contain: 5
First even element in v: 4
No elements in v are divisible by 13
First element indivisible by 13 in v: 4
First odd element in v: 1

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 a range of elements (niebloid)
findfind_iffind_if_not (C++11)	finds the first element satisfying specific criteria (function template)