NAME

std::find_end - std::find_end

Synopsis

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

ForwardIt1 find_end( ForwardIt1 first, (until C++20)
ForwardIt1 last,

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

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

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 BinaryPredicate >
(1)
ForwardIt1 find_end( ForwardIt1 first, (until C++20)
ForwardIt1 last,

ForwardIt2 s_first, ForwardIt2 s_last,
BinaryPredicate p );
template< class ForwardIt1, class ForwardIt2,
class BinaryPredicate >

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

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

ForwardIt1 find_end( ExecutionPolicy&& policy, (4) (since C++17)
ForwardIt1 first, ForwardIt1 last,

ForwardIt2 s_first, ForwardIt2 s_last,
BinaryPredicate 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 do not
participate in overload resolution unless
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
(since C++20) is true.

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 no such sequence is found, last is returned. (until C++11)
If [s_first, s_last) is empty or if no such sequence is found, last is (since C++11)
returned.

Complexity

Does at most \(\scriptsize S\cdot(N-S+1)\)S·(N-S+1) comparisons where \(\scriptsize
S\)S is std::distance(first2, last2) and \(\scriptsize N\)N is std::distance(first1,
last1).

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

First version

template<class ForwardIt1, class ForwardIt2>
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;
}

Second version

template<class ForwardIt1, class ForwardIt2, class BinaryPredicate>
ForwardIt1 find_end(ForwardIt1 first, ForwardIt1 last,
ForwardIt2 s_first, ForwardIt2 s_last,
BinaryPredicate 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

The following code uses find_end() to search for two different sequences of numbers.

// Run this code

#include <algorithm>
#include <iostream>
#include <vector>

int main()
{
std::vector<int> v{1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4};
std::vector<int>::iterator result;

auto check = [&] {
result == v.end()
? std::cout << "sequence not found\n"
: std::cout << "last occurrence is at: "
<< std::distance(v.begin(), result) << "\n";
};

std::vector<int> t1{1, 2, 3};
result = std::find_end(v.begin(), v.end(), t1.begin(), t1.end());
check();

std::vector<int> t2{4, 5, 6};
result = std::find_end(v.begin(), v.end(), t2.begin(), t2.end());
check();
}

Output:

last occurrence is at: 8
sequence not found