Namespaces
Variants
Views
Actions

Difference between revisions of "cpp/algorithm/ranges/contains"

From cppreference.com
< cpp‎ | algorithm‎ | ranges
(→‎Example: remove invalid projections (the projection is required to be regular_invocable, and thus must not modify the elements))
m (FTM.)
 
Line 88: Line 88:
 
{{ftm begin}}
 
{{ftm begin}}
 
{{ftm|__cpp_lib_ranges_contains|value=202207L|std=C++23|{{ttt|std::ranges::contains}} and {{ttt|ranges::contains_subrange}}}}
 
{{ftm|__cpp_lib_ranges_contains|value=202207L|std=C++23|{{ttt|std::ranges::contains}} and {{ttt|ranges::contains_subrange}}}}
−
{{ftm|__cpp_lib_default_template_type_for_algorithm_values|value=202403|std=C++26|[[cpp/language/list_initialization|list-initialization]] for algorithms {{vl|1,2}}}}
+
{{ftm|__cpp_lib_algorithm_default_value_type|value=202403|std=C++26|[[cpp/language/list initialization|List-initialization]] for algorithms {{vl|1,2}}}}
 
{{ftm end}}
 
{{ftm end}}
  
Line 177: Line 177:
  
 
     constexpr std::array<std::complex<double>, 3> nums{<!---->{<!---->{1, 2}, {3, 4}, {5, 6}<!---->}<!---->};
 
     constexpr std::array<std::complex<double>, 3> nums{<!---->{<!---->{1, 2}, {3, 4}, {5, 6}<!---->}<!---->};
−
     #ifdef __cpp_lib_default_template_type_for_algorithm_values
+
     #ifdef __cpp_lib_algorithm_default_value_type
 
         static_assert(ranges::contains(nums, {3, 4}));
 
         static_assert(ranges::contains(nums, {3, 4}));
 
     #else
 
     #else

Latest revision as of 22:44, 20 May 2024

 
C++
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
(C++11)
(C++11)
(C++11)
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
(C++11)
(C++17)
Lexicographical comparison operations
(C++20)
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
 
Constrained algorithms
All names in this menu belong to namespace std::ranges
Non-modifying sequence operations
Modifying sequence operations
Partitioning operations
Sorting operations
Binary search operations (on sorted ranges)
       
       
    
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations
       
       
Permutation operations
Fold operations
Numeric operations
(C++23)            
Operations on uninitialized storage
Return types
 
Defined in header <algorithm>
Call signature
(1)
template< std::input_iterator I, std::sentinel_for<I> S,

          class T,
          class Proj = std::identity >
requires std::indirect_binary_predicate<ranges::equal_to, std::projected<I, Proj>,
                                        const T*>

constexpr bool contains( I first, S last, const T& value, Proj proj = {} );
 (since C++23)
(until C++26)
template< std::input_iterator I, std::sentinel_for<I> S,

          class Proj = std::identity,
          class T = std::projected_value_t<I, Proj> >
requires std::indirect_binary_predicate<ranges::equal_to, std::projected<I, Proj>,
                                        const T*>

constexpr bool contains( I first, S last, const T& value, Proj proj = {} );
 (since C++26)
(2)
template< ranges::input_range R,

          class T,
          class Proj = std::identity >
requires std::indirect_binary_predicate<ranges::equal_to,
                                        std::projected<ranges::iterator_t<R>, Proj>,
                                        const T*>

constexpr bool contains( R&& r, const T& value, Proj proj = {} );
 (since C++23)
(until C++26)
template< ranges::input_range R,

          class Proj = std::identity,
          class T = std::projected_value_t<ranges::iterator_t<R>, Proj> >
requires std::indirect_binary_predicate<ranges::equal_to,
                                        std::projected<ranges::iterator_t<R>, Proj>,
                                        const T*>

constexpr bool contains( R&& r, const T& value, Proj proj = {} );
 (since C++26)
template< std::forward_iterator I1, std::sentinel_for<I1> S1,

          std::forward_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 bool contains_subrange( I1 first1, S1 last1, I2 first2, S2 last2,
                                  Pred pred = {},

                                  Proj1 proj1 = {}, Proj2 proj2 = {} );
 (3) (since C++23)
template< ranges::forward_range R1, ranges::forward_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 bool contains_subrange( R1&& r1, R2&& r2, Pred pred = {},

                                  Proj1 proj1 = {}, Proj2 proj2 = {} );
 (4) (since C++23)
1) Search-based algorithm that checks whether or not a given range contains a value with iterator-sentinel pairs.
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.
3) Search-based algorithm that checks whether or not a given range is a subrange of another range with iterator-sentinel pairs.
4) Same as (3) 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.

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

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

Contents

[edit] Parameters

first, last - the range of elements to examine
r - the range of the elements to examine
value - value to compare the elements to
pred - predicate to apply to the projected elements
proj - projection to apply to the elements

[edit] Return value

1,2) : ranges::find(std::move(first), last, value, proj) != last
3,4) : first2 == last2 || !ranges::search(first1, last1, first2, last2, pred, proj1, proj2).empty()

[edit] Complexity

At most last - first applications of the predicate and projection.

[edit] Notes

Up until C++20, we've had to write std::ranges::find(r, value) != std::ranges::end(r) to determine if a single value is inside a range. And to check if a range contains a subrange of interest, we use not std::ranges::search(haystack, needle).empty(). While this is accurate, it isn't necessarily convenient, and it hardly expresses intent (especially in the latter case). Being able to say std::ranges::contains(r, value) addresses both of these points.

ranges::contains_subrange, same as ranges::search, but as opposed to std::search, provides no access to Searchers (such as Boyer-Moore).

Feature-test macro Value Std Feature
__cpp_lib_ranges_contains 202207L (C++23) std::ranges::contains and ranges::contains_subrange
__cpp_lib_algorithm_default_value_type 202403 (C++26) List-initialization for algorithms (1,2)

[edit] Possible implementation

contains (1,2) 
struct __contains_fn
{
    template<std::input_iterator I, std::sentinel_for<I> S,
             class Proj = std::identity,
             class T = std::projected_value_t<I, Proj>>
    requires std::indirect_binary_predicate<ranges::equal_to, std::projected<I, Proj>,
                                            const T*>
    constexpr bool operator()(I first, S last, const T& value, Proj proj = {}) const
    {
        return ranges::find(std::move(first), last, value, proj) != last;
    }
 
    template<ranges::input_range R,
             class Proj = std::identity,
             class T = std::projected_value_t<ranges::iterator_t<R>, Proj>>
    requires std::indirect_binary_predicate<ranges::equal_to,
                                            std::projected<ranges::iterator_t<R>, Proj>,
                                            const T*>
    constexpr bool operator()(R&& r, const T& value, Proj proj = {}) const
    {
        return (*this)(ranges::begin(r), ranges::end(r), std::move(value), proj);
    }
};
 
inline constexpr __contains_fn contains {};
contains_subrange (3,4) 
struct __contains_subrange_fn
{
    template<std::forward_iterator I1, std::sentinel_for<I1> S1,
             std::forward_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 bool operator()(I1 first1, S1 last1,
                              I2 first2, S2 last2,
                              Pred pred = {},
                              Proj1 proj1 = {}, Proj2 proj2 = {}) const
    {
        return (first2 == last2) ||
               !ranges::search(first1, last1, first2, last2, pred, proj1, proj2).empty();
    }
 
    template<ranges::forward_range R1, ranges::forward_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 bool 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::move(pred),
                       std::move(proj1), std::move(proj2));
    }
};
 
inline constexpr __contains_subrange_fn contains_subrange {};

[edit] Example

Run this code
#include <algorithm>
#include <array>
#include <complex>
 
namespace ranges = std::ranges;
 
int main()
{
    constexpr auto haystack = std::array{3, 1, 4, 1, 5};
    constexpr auto needle = std::array{1, 4, 1};
    constexpr auto bodkin = std::array{2, 5, 2};
 
    static_assert(
        ranges::contains(haystack, 4) &&
       !ranges::contains(haystack, 6) &&
        ranges::contains_subrange(haystack, needle) &&
       !ranges::contains_subrange(haystack, bodkin)
    );
 
    constexpr std::array<std::complex<double>, 3> nums{{{1, 2}, {3, 4}, {5, 6}}};
    #ifdef __cpp_lib_algorithm_default_value_type
        static_assert(ranges::contains(nums, {3, 4}));
    #else
        static_assert(ranges::contains(nums, std::complex<double>{3, 4}));
    #endif
}

[edit] See also

(C++20)(C++20)(C++20)
 finds the first element satisfying specific criteria
(niebloid)[edit]
(C++20)
 searches for the first occurrence of a range of elements
(niebloid)[edit]
(C++20)
 determines if an element exists in a partially-ordered range
(niebloid)[edit]
(C++20)
 returns true if one sequence is a subsequence of another
(niebloid)[edit]
(C++20)(C++20)(C++20)
 checks if a predicate is true for all, any or none of the elements in a range
(niebloid)[edit]
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/algorithm/ranges/contains&oldid=171937"