NAME

std::ranges::mismatch,std::ranges::mismatch_result - std::ranges::mismatch,std::ranges::mismatch_result

Synopsis

Defined in header <algorithm>
Call signature
template< std::input_iterator I1, std::sentinel_for<I1> S1,

std::input_iterator I2, std::sentinel_for<I2> S2,
class Pred = ranges::equal_to,
class Proj1 = std::identity, class Proj2 = std::identity > (1) (since C++20)
requires std::indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
constexpr mismatch_result<I1, I2>
mismatch( I1 first1, S1 last1, I2 first2, S2 last2,

Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {} );
template< ranges::input_range R1, ranges::input_range R2,

class Pred = ranges::equal_to,
class Proj1 = std::identity, class Proj2 = std::identity >
requires std::indirectly_comparable<
ranges::iterator_t<R1>, ranges::iterator_t<R2>, Pred, Proj1, (2) (since C++20)
Proj2>
constexpr mismatch_result<ranges::borrowed_iterator_t<R1>,
ranges::borrowed_iterator_t<R2>>

mismatch( R1&& r1, R2&& r2, Pred pred = {}, Proj1 proj1 = {},
Proj2 proj2 = {} );

Helper types

template<class I1, class I2> (3) (since C++20)
using mismatch_result = ranges::in_in_result<I1, I2>;

Returns the first mismatching pair of projected elements from two ranges: one
defined by [first1, last1) or r1 and another defined by [first2,last2) or r2.

1) Elements are compared using the given binary predicate p.
2) Same as (1), but uses r as the source range, as if using ranges::begin(r) as
first and ranges::end(r) as last.

The function-like entities described on this page are niebloids, that is:

* Explicit template argument lists may not be specified when calling any of them.
* None of them is visible to argument-dependent lookup.
* When one of them is found by normal unqualified lookup for the name to the left
of the function-call operator, it inhibits argument-dependent lookup.

In practice, they may be implemented as function objects, or with special compiler
extensions.

Parameters

first1, last1 - an iterator-sentinel pair denoting the first range of the elements
to compare
r1 - the first range of the elements to compare
first2, last2 - an iterator-sentinel pair denoting the second range of the elements
to compare
r2 - the second range of the elements to compare
pred - predicate to apply to the projected elements
proj1 - projection to apply to the first range of elements
proj2 - projection to apply to the second range of elements

Return value

ranges::mismatch_result with iterators to the first two non-equal elements.

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

Complexity

At most min(last1 - first1, last2 - first2) applications of the predicate and
corresponding projections.

Possible implementation

struct mismatch_fn {
template<std::input_iterator I1, std::sentinel_for<I1> S1,
std::input_iterator I2, std::sentinel_for<I2> S2,
class Pred = ranges::equal_to,
class Proj1 = std::identity, class Proj2 = std::identity>
requires std::indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
constexpr std::mismatch_result<I1, I2>
operator()(I1 first1, S1 last1, I2 first2, S2 last2,
Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const
{
for (; first1 != last1 && first2 != last2; ++first1, (void)++first2) {
if (!std::invoke(pred, std::invoke(proj1, *first1), std::invoke(proj2, *first2))) {
break;
}
}
return {first1, first2};
}

template<ranges::input_range R1, ranges::input_range R2,
class Pred = ranges::equal_to,
class Proj1 = std::identity, class Proj2 = std::identity >
requires std::indirectly_comparable<ranges::iterator_t<R1>, ranges::iterator_t<R2>,
Pred, Proj1, Proj2>
constexpr
ranges::mismatch_result<ranges::borrowed_iterator_t<R1>, ranges::borrowed_iterator_t<R2>>
operator()(R1&& r1, R2&& r2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const
{
return (*this)(ranges::begin(r1), ranges::end(r1),
ranges::begin(r2), ranges::end(r2),
std::ref(pred), std::ref(proj1), std::ref(proj2));
} };

inline constexpr mismatch_fn mismatch;

Example

This program determines 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)

// Run this code

#include <algorithm>
#include <cstddef>
#include <iostream>
#include <ranges>
#include <string_view>

constexpr std::string_view mirror_ends(const std::string_view in)
{
const auto end = std::ranges::mismatch(in, in | std::views::reverse).in1;
const std::size_t length = std::ranges::distance(in.begin(), end);
return { in.cbegin(), length };
}

int main()
{
std::cout << mirror_ends("abXYZba") << '\n'
<< mirror_ends("abca") << '\n'
<< mirror_ends("ABBA") << '\n'
<< mirror_ends("level") << '\n';

using namespace std::literals::string_view_literals;

static_assert("123"sv == mirror_ends("123!@#321"));
static_assert("radar"sv == mirror_ends("radar"));
}

Output:

ab
a
ABBA
level