std::find, std::find_if, std::find_if_not
Defined in header <algorithm>
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template< class InputIt, class T > InputIt find( InputIt first, InputIt last, const T& value ); |
(1) | |
template< class InputIt, class UnaryPredicate > InputIt find_if( InputIt first, InputIt last, |
(2) | |
template< class InputIt, class UnaryPredicate > InputIt find_if_not( InputIt first, InputIt last, |
(3) | (since C++11) |
Returns the first element in the range [first, last)
that satisfies specific criteria:
find
searches for an element equal to value
find_if
searches for an element for which predicate p
returns truefind_if_not
searches for an element for which predicate q
returns falseContents |
[edit] Parameters
first, last | - | the range of elements to examine |
value | - | value to compare the elements to |
p | - | unary predicate which returns true for the required element. The signature of the predicate function should be equivalent to the following: bool pred(const Type &a); The signature does not need to have const &, but the function must not modify the objects passed to it. |
q | - | unary predicate which returns false for the required element. The signature of the predicate function should be equivalent to the following: bool pred(const Type &a); The signature does not need to have const &, but the function must not modify the objects passed to it. |
Type requirements | ||
-InputIt must meet the requirements of InputIterator .
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-UnaryPredicate must meet the requirements of Predicate .
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[edit] Return value
Iterator to the first element satisfying the condition or last
if no such element is found.
[edit] Complexity
At most last
- first
applications of the predicate
[edit] Possible implementation
First version |
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template<class InputIt, class T> InputIt find(InputIt first, InputIt last, const T& value) { for (; first != last; ++first) { if (*first == value) { return first; } } return last; } |
Second version |
template<class InputIt, class UnaryPredicate> InputIt find_if(InputIt first, InputIt last, UnaryPredicate p) { for (; first != last; ++first) { if (p(*first)) { return first; } } return last; } |
Third version |
template<class InputIt, class UnaryPredicate> InputIt find_if_not(InputIt first, InputIt last, UnaryPredicate q) { for (; first != last; ++first) { if (!q(*first)) { return first; } } return last; } |
If you do not have C++11, an equivalent to std::find_if_not is to use std::find_if with the negated predicate.
template<class InputIt, class UnaryPredicate> InputIt find_if_not(InputIt first, InputIt last, UnaryPredicate q) { return std::find_if(first, last, std::not1(q)); } |
[edit] Example
The following example finds an integer in a vector of integers.
#include <iostream> #include <algorithm> #include <vector> #include <iterator> int main() { int n1 = 3; int n2 = 5; std::vector<int> v{0, 1, 2, 3, 4}; auto result1 = std::find(std::begin(v), std::end(v), n1); auto result2 = std::find(std::begin(v), std::end(v), n2); if (result1 != std::end(v)) { std::cout << "v contains: " << n1 << '\n'; } else { std::cout << "v does not contain: " << n1 << '\n'; } if (result2 != std::end(v)) { std::cout << "v contains: " << n2 << '\n'; } else { std::cout << "v does not contain: " << n2 << '\n'; } }
Output:
v contains: 3 v does not contain: 5
[edit] See also
finds the first two adjacent items that are equal (or satisfy a given predicate) (function template) | |
finds the last sequence of elements in a certain range (function template) | |
searches for any one of a set of elements (function template) | |
finds the first position where two ranges differ (function template) | |
searches for a range of elements (function template) | |
(parallelism TS) |
parallelized version of std::find (function template) |
(parallelism TS) |
parallelized version of std::find_if (function template) |
(parallelism TS) |
parallelized version of std::find_if_not (function template) |