NAME¶

std::find_end - std::find_end

Synopsis¶

Defined in header <algorithm>
template< class ForwardIt1, class ForwardIt2 >

ForwardIt1 find_end( ForwardIt1 first, ForwardIt1 last, (1) (constexpr since C++20)

ForwardIt2 s_first, ForwardIt2
s_last );
template< class ExecutionPolicy, class ForwardIt1, class
ForwardIt2 >

ForwardIt1 find_end( ExecutionPolicy&& policy, (2) (since C++17)
ForwardIt1 first, ForwardIt1 last,

ForwardIt2 s_first, ForwardIt2
s_last );
template< class ForwardIt1, class ForwardIt2, class
BinaryPred >

ForwardIt1 find_end( ForwardIt1 first, ForwardIt1 last, (3) (constexpr since C++20)
ForwardIt2 s_first, ForwardIt2
s_last,

BinaryPred p );
template< class ExecutionPolicy,

class ForwardIt1, class ForwardIt2, class
BinaryPred >
ForwardIt1 find_end( ExecutionPolicy&& policy, (4) (since C++17)
ForwardIt1 first, ForwardIt1 last,
ForwardIt2 s_first, ForwardIt2
s_last,

BinaryPred p );

Searches for the last occurrence of the sequence [s_first, s_last) in the range
[first, last).

1) Elements are compared using operator==.
3) Elements are compared using the given binary predicate p.
2,4) Same as (1,3), but executed according to policy.
These overloads participate in overload resolution only if

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true. (until
C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. (since
C++20)

Parameters¶

first, last - the range of elements to examine
s_first, s_last - the range of elements to search for
policy - the execution policy to use. See execution policy for details.
binary predicate which returns true if the elements should be
treated as equal.

The signature of the predicate function should be equivalent to
the following:

bool pred(const Type1 &a, const Type2 &b);

p - While the signature does not need to have const &, the function
must not modify the objects passed to it and must be able to
accept all values of type (possibly const) Type1 and Type2
regardless of value category (thus, Type1 & is not allowed
, nor is Type1 unless for Type1 a move is equivalent to a copy
(since C++11)).
The types Type1 and Type2 must be such that objects of types
ForwardIt1 and ForwardIt2 can be dereferenced and then implicitly
converted to Type1 and Type2 respectively.

Type requirements¶

-
ForwardIt1 must meet the requirements of LegacyForwardIterator.
-
ForwardIt2 must meet the requirements of LegacyForwardIterator.

Return value¶

Iterator to the beginning of last occurrence of the sequence [s_first, s_last) in
range [first, last).

If [s_first, s_last) is empty or if no such sequence is found, last is returned.

Complexity¶

Given \(\scriptsize N\)N as std::distance(first1, last1) and \(\scriptsize S\)S as
std::distance(first2, last2):

1,2) At most \(\scriptsize S\cdot(N-S+1)\)S·(N-S+1) comparisons using operator==.
3,4) At most \(\scriptsize S\cdot(N-S+1)\)S·(N-S+1) applications of the predicate p.

Exceptions¶

The overloads with a template parameter named ExecutionPolicy report errors as
follows:

* If execution of a function invoked as part of the algorithm throws an exception
and ExecutionPolicy is one of the standard policies, std::terminate is called.
For any other ExecutionPolicy, the behavior is implementation-defined.
* If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation¶

find_end (1)
template<class ForwardIt1, class ForwardIt2>
constexpr //< since C++20
ForwardIt1 find_end(ForwardIt1 first, ForwardIt1 last,
ForwardIt2 s_first, ForwardIt2 s_last)
{
if (s_first == s_last)
return last;

ForwardIt1 result = last;
while (true)
{
ForwardIt1 new_result = std::search(first, last, s_first, s_last);
if (new_result == last)
break;
else
{
result = new_result;
first = result;
++first;
}
}
return result;
}
find_end (3)
template<class ForwardIt1, class ForwardIt2, class BinaryPred>
constexpr //< since C++20
ForwardIt1 find_end(ForwardIt1 first, ForwardIt1 last,
ForwardIt2 s_first, ForwardIt2 s_last,
BinaryPred p)
{
if (s_first == s_last)
return last;

ForwardIt1 result = last;
while (true)
{
ForwardIt1 new_result = std::search(first, last, s_first, s_last, p);
if (new_result == last)
break;
else
{
result = new_result;
first = result;
++first;
}
}
return result;
}

Example¶

// Run this code

#include <algorithm>
#include <array>
#include <cmath>
#include <iostream>

auto print_result = [](auto result, const auto& v)
{
result == v.end()
? std::cout << "Sequence not found\n"
: std::cout << "Last occurrence is at: " << std::distance(v.begin(), result)
<< '\n';
};

int main()
{
const auto v = {1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4};

for (auto const& x : {std::array{1, 2, 3}, {4, 5, 6}})
{
auto iter = std::find_end(v.begin(), v.end(), x.begin(), x.end()); // overload (1)
print_result(iter, v);
}

for (auto const& x : {std::array{-1, -2, -3}, {-4, -5, -6}})
{
auto iter = std::find_end(v.begin(), v.end(), x.begin(), x.end(), // overload (3)
[](int x, int y)
{
return std::abs(x) == std::abs(y);
});
print_result(iter, v);
}
}

Output:¶

Last occurrence is at: 8
Sequence not found
Last occurrence is at: 8
Sequence not found

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 1205 C++98 the return value was unclear if returns last in this
[s_first, s_last) is empty case
LWG 2150 C++98 the condition of “sequence occurence” was corrected
incorrect

See also¶

search searches for a range of elements
(function template)
includes returns true if one sequence is a subsequence of another
(function template)
finds the first two adjacent items that are equal (or satisfy a
adjacent_find given predicate)
(function template)
find
find_if finds the first element satisfying specific criteria
find_if_not (function template)
(C++11)
find_first_of searches for any one of a set of elements
(function template)
search_n searches a range for a number of consecutive copies of an element
(function template)
ranges::find_end finds the last sequence of elements in a certain range
(C++20) (niebloid)