std::find_first_of
(on partitioned ranges)
<algorithm>
InputIt find_first_of( InputIt first, InputIt last,
ForwardIt1 find_first_of( ExecutionPolicy&& policy,
ForwardIt1 first, ForwardIt1 last,
InputIt find_first_of( InputIt first, InputIt last,
ForwardIt s_first, ForwardIt s_last,
class ForwardIt1, class ForwardIt2, class BinaryPred >
ForwardIt1 find_first_of( ExecutionPolicy&& policy,
ForwardIt1 first, ForwardIt last,
ForwardIt2 s_first, ForwardIt2 s_last,
Searches the range [
first,
last)
for any of the elements in the range [
s_first,
s_last)
.
std::is_execution_policy_v <std::decay_t <ExecutionPolicy>> is true.
(until C++20)std::is_execution_policy_v <std::remove_cvref_t <ExecutionPolicy>> is true.
(since C++20)The signature of the predicate function should be equivalent to the following:
bool pred(const Type1 &a, const Type2 &b);
While the signature does not need to have const &, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1
and Type2
regardless of value category (thus, Type1 & is not allowed, nor is Type1 unless for Type1
a move is equivalent to a copy(since C++11)).
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.
InputIt
must meet the requirements of LegacyInputIterator.
ForwardIt
must meet the requirements of LegacyForwardIterator.
ForwardIt1
must meet the requirements of LegacyForwardIterator.
ForwardIt2
must meet the requirements of LegacyForwardIterator.
BinaryPred
must meet the requirements of BinaryPredicate.
Iterator to the first element in the range [
first,
last)
that is equal to an element from the range [
s_first,
s_last)
.
If [
s_first,
s_last)
is empty or if no such element is found, last is returned.
Given \(\scriptsize N\)N as std::distance (first, last) and \(\scriptsize S\)S as std::distance (s_first, s_last):
The overloads with a template parameter named ExecutionPolicy
report errors as follows:
ExecutionPolicy
is one of the standard policies, std::terminate is called. For any other ExecutionPolicy
, the behavior is implementation-defined.
find_first_of (1) |
---|
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; } |
find_first_of (3) |
template<class InputIt, class ForwardIt, class BinaryPred> InputIt find_first_of(InputIt first, InputIt last, ForwardIt s_first, ForwardIt s_last, BinaryPred p) { for (; first != last; ++first) for (ForwardIt it = s_first; it != s_last; ++it) if (p(*first, *it)) return first; return last; } |
The following code searches for any of specified integers in a vector of integers:
#include <algorithm> #include <iostream> #include <vector> auto print_sequence = [](const auto id, const auto& seq, int pos = -1) { std::cout << id << "{ "; for (int i{}; auto const& e : seq) { const bool mark{i == pos}; std::cout << (i++ ? ", " : ""); std::cout << (mark ? "[ " : "") << e << (mark ? " ]" : ""); } std::cout << " }\n"; }; int main() { const std::vector <int> v{0, 2, 3, 25, 5}; const auto t1 = {19, 10, 3, 4}; const auto t2 = {1, 6, 7, 9}; auto find_any_of = [](const auto& v, const auto& t) { const auto result = std::find_first_of(v.begin(), v.end(), t.begin(), t.end()); if (result == v.end()) { std::cout << "No elements of v are equal to any element of "; print_sequence("t = ", t); print_sequence("v = ", v); } else { const auto pos = std::distance (v.begin(), result); std::cout << "Found a match (" << *result << ") at position " << pos; print_sequence(", where t = ", t); print_sequence("v = ", v, pos); } }; find_any_of(v, t1); find_any_of(v, t2); }
Output:
Found a match (3) at position 2, where t = { 19, 10, 3, 4 } v = { 0, 2, [ 3 ], 25, 5 } No elements of v are equal to any element of t = { 1, 6, 7, 9 } v = { 0, 2, 3, 25, 5 }
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR | Applied to | Behavior as published | Correct behavior |
---|---|---|---|
LWG 576 | C++98 | first and last needed to be LegacyForwardIterators | they only need to be LegacyInputIterators |
LWG 1205 | C++98 | the return value was unclear if [ s_first, s_last) is empty
|
returns last in this case |