# std::experimental::ranges::mismatch

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< cpp‎ | experimental‎ | ranges

Defined in header `<experimental/ranges/algorithm>` |  |
template< InputIterator I1, Sentinel<I1> S1, InputIterator I2, Sentinel<I2> S2, class Proj1 = ranges::identity, class Proj2 = ranges::identity, class Pred = ranges::equal_to<> > requires IndirectRelation<Pred, projected<I1, Proj1>, projected<I2, Proj2>> auto mismatch(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = Pred{}, Proj1 proj1 = Proj1{}, Proj2 proj2 = Proj2{}) -> ranges::tagged_pair<tag::in1(I1), tag::in2(I2)>; | (1) | (ranges TS)
template< InputRange R1, InputRange R2, class Proj1 = ranges::identity, class Proj2 = ranges::identity, class Pred = ranges::equal_to<> > requires IndirectRelation<Pred, projected<ranges::iterator_t<R1>, Proj1>, projected<ranges::iterator_t<R2>, Proj2>> auto mismatch(R1&& r1, R2&& r2, Pred pred = Pred{}, Proj1 proj1 = Proj1{}, Proj2 proj2 = Proj2{}) -> ranges::tagged_pair<tag::in1(ranges::safe_iterator_t<R1>), tag::in2(ranges::safe_iterator_t<R2>)>; | (2) | (ranges TS)
template< InputIterator I1, Sentinel<I1> S1, class I2, class Pred = ranges::equal_to<>, class Proj1 = ranges::identity, class Proj2 = ranges::identity > requires InputIterator<std::decay_t<I2>> && !Range<I2> && IndirectRelation<Pred, projected<I1, Proj1>, projected<std::decay_t<I2>, Proj2>> auto mismatch(I1 first1, S1 last1, I2&& first2_, Pred pred = Pred{}, Proj1 proj1 = Proj1{}, Proj2 proj2 = Proj2{}) -> ranges::tagged_pair<tag::in1(I1), tag::in2(std::decay_t<I2>)>; | (3) | (ranges TS) (deprecated)
template< InputRange R1, class I2, class Pred = ranges::equal_to<>, class Proj1 = ranges::identity, class Proj2 = ranges::identity> requires InputIterator<std::decay_t<I2>> && !Range<I2> && IndirectRelation<Pred, projected<ranges::iterator_t<R1>, Proj1>, projected<std::decay_t<I2>, Proj2>> auto mismatch(R1&& r1, I2&& first2_, Pred pred = Pred{}, Proj1 proj1 = Proj1{}, Proj2 proj2 = Proj2{}) -> ranges::tagged_pair<tag::in1(ranges::safe_iterator_t<Rng1>), tag::in2(std::decay_t<I2>)>; | (4) | (ranges TS) (deprecated)

1) Returns the first mismatching pair of elements from two ranges: one defined by `[first1, last1)` and another defined by `[first2, last2)`.
2) Same as (1), but uses `r1` as the first source range and `r2` as the second source range, as if using ranges::begin(r1) as `first1`, ranges::end(r1) as `last1`, ranges::begin(r2) as `first2`, and ranges::end(r2) as `last2`.
3) Same as (1), but behaves as if `first2` is std::decay_t<I2> first2 = std::forward<I2>(first2_); and `last2` is ranges::unreachable{}. The underlying algorithm never increments `first2` more than last1 - first1 times.
4) Same as (3), but uses `r1` as the first source range, as if using ranges::begin(r1) as `first1` and ranges::end(r1) as `last1`.

Elements are compared using `pred` to the projected elements of the two ranges, as if by ranges::invoke(pred, ranges::invoke(proj1, *i), ranges::invoke(proj2, *j)).

Notwithstanding the declarations depicted above, the actual number and order of template parameters for algorithm declarations is unspecified. Thus, if explicit template arguments are used when calling an algorithm, the program is probably non-portable.

### Parameters

first1, last1 | - | the first range of the elements
r1 | - | the first range of the elements
first2, last2 | - | the second range of the elements
r2 | - | the second range of the elements
first2_ | - | the beginning of the second range of the elements
pred | - | predicate to apply to the projected elements
proj1 | - | projection to apply to the elements in the first range
proj2 | - | projection to apply to the elements in the second range

### Return value

A `tagged_pair` object with iterators to the first two non-equal elements (the iterator from the first range has the tag in1 and the iterator from the second range has the tag in2).

If no mismatches are found when the comparison reaches `last1` or `last2`, whichever happens first, the pair holds the end iterator and the corresponding iterator from the other range.

### Complexity

At most `last1` - `first1` applications of the predicate and each projection.

### Possible implementation

    template< InputIterator I1, Sentinel<I1> S1, InputIterator I2, Sentinel<I2> S2,
              class Proj1 = ranges::identity, class Proj2 = ranges::identity,
              class Pred = ranges::equal_to<> >
      requires IndirectRelation<Pred, projected<I1, Proj1>, projected<I2, Proj2>>
    auto mismatch(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = Pred{},
                  Proj1 proj1 = Proj1{}, Proj2 proj2 = Proj2{})
      -> ranges::tagged_pair<tag::in1(I1), tag::in2(I2)>
    {
        while (first1 != last1 && first2 != last2 &&
               ranges::invoke(pred, ranges::invoke(proj1, *first1),
                                    ranges::invoke(proj2, *first2))) {
            ++first1;
            ++first2;
        }
        return {first1, first2};
    }

### Example

| This section is incomplete Reason: no example

### See also

mismatch | finds the first position where two ranges differ (function template)
equal | determines if two sets of elements are the same (function template)
find find_if find_if_not | 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)

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