Namespaces
Variants
Views
Actions

std::find_first_of

From cppreference.com
< cpp‎ | algorithm
 
 
Algorithm library
Execution policies (C++17)
Non-modifying sequence operations
(C++11)(C++11)(C++11)
(C++17)
find_first_of
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
(C++11)
Binary search operations
Set operations (on sorted ranges)
Heap operations
(C++11)
Minimum/maximum operations
(C++11)
(C++17)

Permutations
Numeric operations
C library
 
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)
template< class ExecutionPolicy, class InputIt, class ForwardIt >

InputIt find_first_of( ExecutionPolicy&& policy, InputIt first, InputIt last,

                       ForwardIt s_first, ForwardIt s_last );
(2) (since C++17)
(3)
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)
template< class ExecutionPolicy, class InputIt, class ForwardIt, class BinaryPredicate >

InputIt find_first_of( ExecutionPolicy&& policy, InputIt first, InputIt last,

                       ForwardIt s_first, ForwardIt s_last, BinaryPredicate p );
(4) (since C++17)

Searches the range [first, last) for any of the elements in the range [s_first, s_last).

1) Elements are compared using operator==.
3) Elements are compared using the given binary predicate p.
2,4) Same as (1,3), but executed according to policy. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

Contents

[edit] Parameters

first, last - the range of elements to examine
s_first, s_last - the range of elements to search for
policy - the execution policy to use. See execution policy for details.
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.

[edit] 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.

[edit] Complexity

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

[edit] Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

  • If execution of a function invoked as part of the algorithm throws an exception, std::terminate is called.
  • If the algorithm fails to allocate memory, std::bad_alloc is thrown.

[edit] 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;
}

[edit] 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:

found a match at 1

[edit] See also

finds the first element satisfying specific criteria
(function template) [edit]
parallelized version of std::find_first_of
(function template) [edit]