std::ranges::find_last, std::ranges::find_last_if, std::ranges::find_last_if_not
Defined in header <algorithm> |
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|---|---|---|
| Call signature | ||
|
(1) | (since C++23) |
|
(2) | (since C++23) |
|
(3) | (since C++23) |
|
(4) | (since C++23) |
|
(5) | (since C++23) |
|
(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.
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_ranges_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 (1-2) |
|---|
|
| find_last_if (3-4) |
|
| find_last_if_not (5-6) |
|
Example
#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
|
(C++20)
|
finds the last sequence of elements in a certain range (niebloid) |
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(C++20)(C++20)(C++20)
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finds the first element satisfying specific criteria (niebloid) |
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(C++20)
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searches for a range of elements (niebloid) |
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(C++20)
|
returns true if one sequence is a subsequence of another(niebloid) |
|
(C++20)
|
determines if an element exists in a partially-ordered range (niebloid) |
|
(C++23)(C++23)
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checks if the range contains the given element or subrange (niebloid) |
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