std::find_first_of

Defined in header <algorithm>

(1)

template< class ForwardIt1, class ForwardIt2 >
ForwardIt1 find_first_of( ForwardIt1 first, ForwardIt1 last,
                          ForwardIt2 s_first, ForwardIt2 s_last );

(until C++11)

template< class InputIt, class ForwardIt >
InputIt find_first_of( InputIt first, InputIt last,
                       ForwardIt s_first, ForwardIt s_last );

(since C++11)

(2)

template< class ForwardIt1, class ForwardIt2, class BinaryPredicate >
ForwardIt1 find_first_of( ForwardIt1 first, ForwardIt1 last,
                          ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p );

(until C++11)

template< class InputIt, class ForwardIt, class BinaryPredicate >
InputIt find_first_of( InputIt first, InputIt last,
                       ForwardIt s_first, ForwardIt s_last, BinaryPredicate p );

(since C++11)

Searches the range [first, last) for any of the elements in the range [s_first, s_last). The first version uses operator== to compare the elements, the second version uses the given binary predicate p.

Parameters

first, last	-	the range of elements to examine
s_first, s_last	-	the range of elements to search for
p	-	binary predicate which returns `true` if the elements should be treated as equal. The signature of the predicate function should be equivalent to the following: `bool pred(const Type1 &a, const Type2 &b);` The signature does not need to have `const &`, but the function must not modify the objects passed to it. The types `Type1` and `Type2` must be such that objects of types `ForwardIt1` and `ForwardIt2` can be dereferenced and then implicitly converted to `Type1` and `Type2` respectively.
Type requirements
- `InputIt` must meet the requirements of `InputIterator`.
- `ForwardIt1` must meet the requirements of `ForwardIterator`.
- `ForwardIt2` must meet the requirements of `ForwardIterator`.

Return value

Iterator to the first element in the range [first, last) that is equal to an element from the range [s_first; s_last). If no such element is found, last is returned.

Complexity

Does at most (S*N) comparisons where S = distance(s_first, s_last) and N = distance(first, last).

Possible implementation

First version

template<class InputIt, class ForwardIt>
InputIt find_first_of(InputIt first, InputIt last,
                      ForwardIt s_first, ForwardIt s_last)
{
    for (; first != last; ++first) {
        for (ForwardIt it = s_first; it != s_last; ++it) {
            if (*first == *it) {
                return first;
            }
        }
    }
    return last;
}

Second version

template<class InputIt, class ForwardIt, class BinaryPredicate>
InputIt find_first_of(InputIt first, InputIt last,
                      ForwardIt s_first, ForwardIt s_last,
                      BinaryPredicate p)
{
    for (; first != last; ++first) {
        for (ForwardIt it = s_first; it != s_last; ++it) {
            if (p(*first, *it)) {
                return first;
            }
        }
    }
    return last;
}

Example

The following code searches for any of specified integers in a vector of integers:

#include <algorithm>
#include <iostream>
#include <vector>
  
int main()
{
    std::vector<int> v{0, 2, 3, 25, 5};
    std::vector<int> t{3, 19, 10, 2};
  
    auto result = std::find_first_of(v.begin(), v.end(), t.begin(), t.end());
  
    if (result == v.end()) {
        std::cout << "no elements of v were equal to 3, 19, 10 or 2\n";
    } else {
        std::cout << "found a match at "
                  << std::distance(v.begin(), result) << "\n";
    }
 }

Output:

1	`found a match at 1`

findfind_iffind_if_not (C++11)	finds the first element satisfying specific criteria (function template)
std::experimental::parallel::find_first_of (parallelism TS)	parallelized version of `std::find_first_of` (function template)