std::search to find a rightmost subsequence - c++

Question

I am trying to find a rightmost subsequence in a range with std::search and std::make_reverse_iterator.
However the iterator returned always point to the start of a range. What am I doing wrong?
TEST(basic_test, find_from_right)
{
std::vector<uint8_t> array{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
std::array<uint8_t, 2> subSeq{3, 4};
auto found = std::search(std::make_reverse_iterator(array.cend()),
std::make_reverse_iterator(array.cbegin()),
subSeq.cbegin(),
subSeq.cend());
// makes no difference
// std::make_reverse_iterator(subSeq.cend()),
// std::make_reverse_iterator(subSeq.cbegin()));
auto distance = std::distance(found.base(), array.cbegin());
EXPECT_EQ(distance, 3);
}
Output:
Failure
Expected equality of these values:
distance
Which is: 0
3
I have a function that is provided with 2 template RandomIterators, so I have to call std::make_reverse_iterator. These containers are just for the sake of reproducing the problem and compiling the example.

Answer 1

I think this could solve your problem (if you are okay with C++17):
From https://en.cppreference.com/w/cpp/algorithm/find_end:
#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;
std::vector<int> t1{1, 2, 3};
result = std::find_end(v.begin(), v.end(), t1.begin(), t1.end());
if (result == v.end()) {
std::cout << "sequence not found\n";
} else {
std::cout << "last occurrence is at: "
<< std::distance(v.begin(), result) << "\n";
}
std::vector<int> t2{4, 5, 6};
result = std::find_end(v.begin(), v.end(), t2.begin(), t2.end());
if (result == v.end()) {
std::cout << "sequence not found\n";
} else {
std::cout << "last occurrence is at: "
<< std::distance(v.begin(), result) << "\n";
}
}
So in your case:
auto result = std::find_end(array.begin(), array.end(), subSeq.begin(), subSeq.end());
if (result == array.end()) {
std::cout << "sequence not found\n";
} else {
std::cout << "last occurrence is at: "
<< std::distance(array.begin(), result) << "\n";
}