std::mismatch

 

C++

Language

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

 

Algorithm library

Functions
Non-modifying sequence operations
all_of any_of none_of (C++11) (C++11) (C++11) for_each count count_if mismatch equal	find find_if find_if_not (C++11) find_end find_first_of adjacent_find search search_n
Modifying sequence operations
copy copy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n remove remove_if remove_copy remove_copy_if	replace replace_if replace_copy replace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffle shuffle   (C++11) unique unique_copy
Partitioning operations
is_partitioned (C++11) partition partition_copy (C++11)	stable_partition partition_point (C++11)
Sorting operations (on sorted ranges)
is_sorted (C++11) is_sorted_until (C++11) sort	partial_sort partial_sort_copy stable_sort nth_element
Binary search operations (on sorted ranges)
lower_bound upper_bound	binary_search equal_range
Set operations (on sorted ranges)
merge inplace_merge includes	set_difference set_intersection set_symmetric_difference set_union
Heap operations
is_heap is_heap_until (C++11) make_heap	push_heap pop_heap sort_heap
Minimum/maximum operations
max max_element min min_element minmax (C++11) minmax_element (C++11)	lexicographical_compare is_permutation (C++11) next_permutation prev_permutation
Numeric operations
iota (C++11) accumulate inner_product	adjacent_difference partial_sum
C library
qsort	bsearch

 

Defined in header <algorithm>
template< class InputIterator1, class InputIterator2 > std::pair<InputIterator1,InputIterator2>     mismatch( InputIterator1 first1,               InputIterator1 last1,               InputIterator2 first2 );	(1)
template< class InputIterator1, class InputIterator2, class BinaryPredicate > std::pair<InputIterator1,InputIterator2>     mismatch( InputIterator1 first1,               InputIterator1 last1,               InputIterator2 first2,               BinaryPredicate p );	(2)

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.

Parameters

first1, last1	-	the first range of the elements
first2	-	the beginning of the second range of the elements
p	-	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); The signature does not need to have const &, but the function must not modify the objects passed to it. The types  Type1 and  Type2 must be such that objects of types InputIterator1 and InputIterator2 can be dereferenced and then implicitly converted to  Type1 and  Type2 respectively. ​

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.

Complexity

At most last1 - first1 applications of the predicate

Possible implementation

First version
template<class InputIterator1, class InputIterator2> std::pair<InputIterator1, InputIterator2> mismatch(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2) { while (first1 != last1 && *first1 == *first2) { ++first1, ++first2; } return std::make_pair(first1, first2); }
Second version
template<class InputIterator1, class InputIterator2, class BinaryPredicate> std::pair<InputIterator1, InputIterator2> mismatch(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, BinaryPredicate p) { while (first1 != last1 && p(*first1, *first2)) { ++first1, ++first2; } return std::make_pair(first1, first2); }

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

See also

equal	determines if two sets of elements are the same (function template)
find find_if find_if_not (C++11)	finds the first element satisfying specific criteria (function template)
lexicographical_compare	returns true if one range is lexicographically less than another (function template)
search	searches for a range of elements (function template)