std::ranges::find, std::ranges::find_if, std::ranges::find_if_not
From cppreference.com
| Defined in header <algorithm>
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| Call signature |
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| (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) |
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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) |
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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 algorithm function objects (informally known as 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.
Parameters
| first, last | - | the iterator-sentinel pair defining 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 (1) |
|---|
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;
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| find_if (3) |
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;
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| find_if_not (5) |
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;
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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
(C++20) |
finds the first two adjacent items that are equal (or satisfy a given predicate) (algorithm function object) |
(C++20) |
finds the last sequence of elements in a certain range (algorithm function object) |
(C++20) |
searches for any one of a set of elements (algorithm function object) |
(C++20) |
finds the first position where two ranges differ (algorithm function object) |
(C++20) |
searches for the first occurrence of a range of elements (algorithm function object) |
(C++11) |
finds the first element satisfying specific criteria (function template) |