std::mismatch

From Cppreference

Returns the first mismatching pair of elements from two ranges: one defined by [first1, last1) and another starting at first2. The first version of the function uses operator== to compare the elements, the second version uses the given binary predicate p.

[edit] Parameters

[edit] Return value

std::pair with iterators to the first two non-equivalent elements, or, if no different elements found, pair with last1 and the corresponding iterator from the second range.

[edit] Complexity

At most last1 - first1 applications of the predicate

[edit] Equivalent function

template<class InputIterator1, class InputIterator2>
std::pair<InputIterator1, InputIterator2>
    mismatch(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2)
{
    for (; first1 != last1; ++first1, ++first2) {
        if (*first1 != *first2) {
            return std::make_pair(first1, first2);
        }
    }
    return std::make_pair(first1, first2);
}

template<class InputIterator1, class InputIterator2, class BinaryPredicate>
std::pair<InputIterator1, InputIterator2>
    mismatch(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, BinaryPredicate p)
{
    for (; first1 != last1; ++first1, ++first2) {
        if (!p(*first1, *first2)) {
            return std::make_pair(first1, first2);
        }
    }
    return std::make_pair(first1, first2);
}

[edit] Example

This program determines the the longest substring that is simultaneously found at the very beginning of the given string and at the very end of it, in reverse order (possibly overlapping)

#include <iostream>
#include <string>
#include <algorithm>
 
std::string mirror_ends(const std::string& in)
{
    return std::string(in.begin(),
                       std::mismatch(in.begin(), in.end(), in.rbegin()).first);
}
 
int main()
{
    std::cout << mirror_ends("abXYZba") << '\n'
              << mirror_ends("abca") << '\n'
              << mirror_ends("aba") << '\n';
}

Output:

ab
a
aba

[edit] See also