std::experimental::ranges::search_n

From cppreference.com
< cpp‎ | experimental‎ | ranges
C++
Experimental
Technical Specification
Filesystem library (filesystem TS)
Library fundamentals (library fundamentals TS)
Library fundamentals 2 (library fundamentals TS v2)
Library fundamentals 3 (library fundamentals TS v3)
Extensions for parallelism (parallelism TS)
Extensions for parallelism 2 (parallelism TS v2)
Extensions for concurrency (concurrency TS)
Extensions for concurrency 2 (concurrency TS v2)
Concepts (concepts TS)
Ranges (ranges TS)
Reflection (reflection TS)
Mathematical special functions (special functions TR)
Experimental Non-TS
Pattern Matching
Linear Algebra
std::execution
Contracts
2D Graphics
Ranges
Algorithms library
Non-modifying sequence operations
Modifying sequence operations
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Permutations
template < ForwardIterator I, Sentinel<I> S, class T,

class Pred = ranges::equal_to <>, class Proj = ranges::identity >
    requires IndirectlyComparable<I, const T*, Pred, Proj>
I search_n( I first, S last, ranges:: difference_type_t <I> count,

const T& value, Pred pred = Pred{ }, Proj proj = Proj{ } ) ;
(1) (ranges TS)
template < ForwardRange R, class T, class Pred = ranges::equal_to <>,

class Proj = ranges::identity >
    requires IndirectlyComparable< ranges::iterator_t <R>, const T*, Pred, Proj>
ranges::safe_iterator_t <R> search_n( R&& r,
                                     ranges:: difference_type_t < ranges::iterator_t <R>> count,

const T& value, Pred pred = Pred{ }, Proj proj = Proj{ } ) ;
(2) (ranges TS)
1) Searches the range [ first ,  last ) for the first sequence of count elements whose projected values are each equal to the given value value according to the predicate pred
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

Parameters

first, last - the range of elements to examine
r - the range of elements to examine
count - the length of the sequence to search for
value - the value to search for
pred - the predicate that compares the projected elements with value
proj - the projection to apply to the elements

Return value

Iterator to the beginning of the found sequence in the range [ first ,  last ) . If no such sequence is found, an iterator that compares equal to last

Complexity

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

Possible implementation

template<ForwardIterator I, Sentinel<I> S, class T,
         class Pred = ranges::equal_to<>, class Proj = ranges::identity>
    requires IndirectlyComparable<I, const T*, Pred, Proj>
I search_n(I first, S last, ranges::difference_type_t<I> count,
           const T& value, Pred pred = Pred{}, Proj proj = Proj{})
{
    for (; first != last; ++first)
    {
        if (!ranges::invoke(pred, ranges::invoke(proj, *first), value))
            continue;
 
        I candidate = first;
        ranges::difference_type_t<I> cur_count = 0;
 
        while (true)
        {
            ++cur_count;
            if (cur_count == count)
                // success
                return candidate;
 
            ++first;
            if (first == last)
                // exhausted the list
                return first;
 
            if (!ranges::invoke(pred, ranges::invoke(proj, *first), value))
                // too few in a row
                break;
        }
    }
    return first;
}

Example

This section is incomplete
Reason: no example

See also

 searches for the first occurrence of a number consecutive copies of an element in a range
(function template)
finds the last sequence of elements in a certain range
(function template)
finds the first element satisfying specific criteria
(function template)
searches for a range of elements
(function template)
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/experimental/ranges/algorithm/search_n&oldid=155288