std::find, std::find_if, std::find_if_not - cppreference.com (original) (raw)

Returns an iterator to the first element in the range [first, last) that satisfies specific criteria (or last if there is no such iterator).

1. find searches for an element equal to value (using operator==).

2. find_if searches for an element for which predicate p returns true.

3. find_if_not searches for an element for which predicate q returns false.

2,4,6) Same as (1,3,5), but executed according to policy.

These overloads participate in overload resolution only if all following conditions are satisfied:

Contents

• 1 Parameters
• 2 Return value
• 3 Complexity
• 4 Exceptions
• 5 Possible implementation
• 6 Notes
• 7 Example
• 8 Defect reports
• 9 See also

[edit] Parameters

[edit] Return value

The first iterator it in the range [first, last) satisfying the following condition or last if there is no such iterator:

1,2) *it == value is true.

3,4) p(*it) is true.

5,6) q(*it) is false.

[edit] Complexity

Given \(\scriptsize N\)N as std::distance(first, last):

1,2) At most \(\scriptsize N\)N comparisons with value using operator==.

3,4) At most \(\scriptsize N\)N applications of the predicate p.

5,6) At most \(\scriptsize N\)N applications of the predicate q.

[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 and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
• If the algorithm fails to allocate memory, std::bad_alloc is thrown.

[edit] Possible implementation

[edit] Notes

If C++11 is not available, an equivalent to std::find_if_not is to use std::find_if with the negated predicate.

template<class InputIt, class UnaryPred> InputIt find_if_not(InputIt first, InputIt last, UnaryPred q) { return std::find_if(first, last, std::not1(q)); }

[edit] Example

The following example finds numbers in given sequences.

#include #include #include #include #include #include #include   bool is_even(int i) { return i % 2 == 0; }   void example_contains() { const auto haystack = {1, 2, 3, 4};   for (const int needle : {3, 5}) if (std::find(haystack.begin(), haystack.end(), needle) == haystack.end()) std::cout << "haystack does not contain " << needle << '\n'; else std::cout << "haystack contains " << needle << '\n'; }   void example_predicate() { for (const auto& haystack : {std::array{3, 1, 4}, {1, 3, 5}}) { const auto it = std::find_if(haystack.begin(), haystack.end(), is_even); if (it != haystack.end()) std::cout << "haystack contains an even number " << *it << '\n'; else std::cout << "haystack does not contain even numbers\n"; } }   void example_list_init() { std::vector<std::complex> haystack{{4.0, 2.0}}; #ifdef __cpp_lib_algorithm_default_value_type // T gets deduced making list-initialization possible const auto it = std::find(haystack.begin(), haystack.end(), {4.0, 2.0}); #else const auto it = std::find(haystack.begin(), haystack.end(), std::complex{4.0, 2.0}); #endif assert(it == haystack.begin());
}   int main() { example_contains(); example_predicate(); example_list_init(); }

Output:

haystack contains 3 haystack does not contain 5 haystack contains an even number 4 haystack does not contain even numbers

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also