std::ranges::find, std::ranges::find_if, std::ranges::find_if_not
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
#include <algorithm>
#include <iostream>
#include <iterator>
int main()
{
namespace ranges = std::ranges;
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";
}
}
Output:
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) (niebloid) |
|
(C++20)
|
finds the last sequence of elements in a certain range (niebloid) |
|
(C++20)
|
searches for any one of a set of elements (niebloid) |
|
(C++20)
|
finds the first position where two ranges differ (niebloid) |
|
(C++20)
|
searches for a range of elements (niebloid) |
|
(C++11)
|
finds the first element satisfying specific criteria (function template) |
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