Difference between revisions of "cpp/algorithm/find first of"
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{{dcl header | algorithm}} | {{dcl header | algorithm}} | ||
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template< class ForwardIt1, class ForwardIt2 > | template< class ForwardIt1, class ForwardIt2 > | ||
ForwardIt1 find_first_of( ForwardIt1 first, ForwardIt1 last, | ForwardIt1 find_first_of( ForwardIt1 first, ForwardIt1 last, | ||
ForwardIt2 s_first, ForwardIt2 s_last ); | ForwardIt2 s_first, ForwardIt2 s_last ); | ||
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template< class InputIt, class ForwardIt > | template< class InputIt, class ForwardIt > | ||
InputIt find_first_of( InputIt first, InputIt last, | InputIt find_first_of( InputIt first, InputIt last, | ||
ForwardIt s_first, ForwardIt s_last ); | ForwardIt s_first, ForwardIt s_last ); | ||
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template< class ForwardIt1, class ForwardIt2, class BinaryPredicate > | template< class ForwardIt1, class ForwardIt2, class BinaryPredicate > | ||
ForwardIt1 find_first_of( ForwardIt1 first, ForwardIt1 last, | ForwardIt1 find_first_of( ForwardIt1 first, ForwardIt1 last, | ||
ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p ); | ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p ); | ||
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template< class InputIt, class ForwardIt, class BinaryPredicate > | template< class InputIt, class ForwardIt, class BinaryPredicate > | ||
InputIt find_first_of( InputIt first, InputIt last, | InputIt find_first_of( InputIt first, InputIt last, | ||
ForwardIt s_first, ForwardIt s_last, BinaryPredicate p ); | ForwardIt s_first, ForwardIt s_last, BinaryPredicate p ); | ||
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Revision as of 08:59, 9 June 2013
| Defined in header <algorithm>
|
||
| (1) | ||
| template< class ForwardIt1, class ForwardIt2 > ForwardIt1 find_first_of( ForwardIt1 first, ForwardIt1 last, |
(until C++11) | |
| template< class InputIt, class ForwardIt > InputIt find_first_of( InputIt first, InputIt last, |
(since C++11) | |
| (2) | ||
| template< class ForwardIt1, class ForwardIt2, class BinaryPredicate > ForwardIt1 find_first_of( ForwardIt1 first, ForwardIt1 last, |
(until C++11) | |
| template< class InputIt, class ForwardIt, class BinaryPredicate > InputIt find_first_of( InputIt first, InputIt last, |
(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.
Contents |
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); 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) |
| Type requirements
Template:par req concept Template:par req concept Template:par req concept | ||
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:
found a match at 1
See also
| (C++11) |
finds the first element satisfying specific criteria (function template) |
