# std::experimental::ranges::find, std::experimental::ranges::find_if, std::experimental::ranges::find_if_not

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< cpp‎ | experimental‎ | ranges

Defined in header `<experimental/ranges/algorithm>` |  |
template< InputIterator I, Sentinel<I> S, class T, class Proj = ranges::identity > requires IndirectRelation<ranges::equal_to<>, projected<I, Proj>, const T*> I find(I first, S last, const T& value, Proj proj = Proj{}); | (1) | (ranges TS)
template< InputRange R, class T, class Proj = ranges::identity > requires IndirectRelation<ranges::equal_to<>, projected<ranges::iterator_t<R>, Proj>, const T*> ranges::safe_iterator_t<R> find(R&& r, const T& value, Proj proj = Proj{}); | (2) | (ranges TS)
template< InputIterator I, Sentinel<I> S, class Proj = ranges::identity, IndirectUnaryPredicate<projected<I, Proj>> Pred > I find_if(I first, S last, Pred pred, Proj proj = Proj{}); | (3) | (ranges TS)
template< InputRange R, class Proj = ranges::identity, IndirectUnaryPredicate<projected<ranges::iterator_t<R>, Proj>> Pred > ranges::safe_iterator_t<R> find_if(R&& r, Pred pred, Proj proj = Proj{}); | (4) | (ranges TS)
template< InputIterator I, Sentinel<I> S, class Proj = ranges::identity, IndirectUnaryPredicate<projected<I, Proj>> Pred > I find_if_not(I first, S last, Pred pred, Proj proj = Proj{}); | (5) | (ranges TS)
template< InputRange R, class Proj = ranges::identity, IndirectUnaryPredicate<projected<ranges::iterator_t<R>, Proj>> Pred > ranges::safe_iterator_t<R> find_if_not(R&& r, Pred pred, Proj proj = Proj{}); | (6) | (ranges TS)

Returns the first element in the range `[first, last)` that satisfies specific criteria:

1) `find` searches for an element whose projected value is equal to `value` (i.e., value == ranges::invoke(proj, *i)).
3) `find_if` searches for an element for whose projected value predicate `p` returns true (i.e., ranges::invoke(pred, ranges::invoke(proj, *i))) is true).
5) `find_if_not` searches for an element for whose projected value predicate `q` returns false (i.e., ranges::invoke(pred, ranges::invoke(proj, *i))) is false).
2,4,6) Same as (1,3,5), but uses `r` as the source range, as if using ranges::begin(r) as `first` and ranges::end(r) as `last`.

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

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

### Return value

Iterator to the first element satisfying the condition. If no such element is found, returns an iterator that compares equal to `last`.

### Complexity

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

### Possible implementation

First version

    template< InputIterator I, Sentinel<I> S, class T, class Proj = ranges::identity >
      requires IndirectRelation<ranges::equal_to<>, projected<I, Proj>, const T*>
    I find(I first, S last, const T& value, Proj proj = Proj{})
    {
        for (; first != last; ++first) {
            if (ranges::invoke(proj, *first) == value) break;
        }
        return first;
    }

Second version

    template< InputIterator I, Sentinel<I> S, class Proj = ranges::identity,
              IndirectUnaryPredicate<projected<I, Proj>> Pred >
    I find_if(I first, S last, Pred pred, Proj proj = Proj{})
    {
        for (; first != last; ++first) {
            if (ranges::invoke(pred, ranges::invoke(proj, *first))) break;
        }
        return first;
    }

Third version

    template< InputIterator I, Sentinel<I> S, class Proj = ranges::identity,
              IndirectUnaryPredicate<projected<I, Proj>> Pred >
    I find_if_not(I first, S last, Pred pred, Proj proj = Proj{})
    {
        for (; first != last; ++first) {
            if (!ranges::invoke(pred, ranges::invoke(proj, *first))) break;
        }
        return first;
    }

### Example

| This section is incomplete Reason: no example

### See also

find find_if find_if_not (C++11) | finds the first element satisfying specific criteria (function template)
adjacent_find | finds the first two adjacent items that are equal (or satisfy a given predicate) (function template)
find_end | finds the last sequence of elements in a certain range (function template)
find_first_of | searches for any one of a set of elements (function template)
mismatch | finds the first position where two ranges differ (function template)
search | searches for a range of elements (function template)

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