Std::find_if_not (3) Linux Manual Page

std::find,std::find_if,std::find_if_not – std::find,std::find_if,std::find_if_not

Synopsis

Defined in header<algorithm>

    template <class InputIt, class T>
    (until C++ 20)

        InputIt find(InputIt first, InputIt last, const T &value);

template <class InputIt, class T>
(since C++ 20)

    constexpr InputIt find(InputIt first, InputIt last, const T &value);

template <class ExecutionPolicy, class ForwardIt, class T>
(2)(since C++ 17)

    ForwardIt find(ExecutionPolicy &&policy, ForwardIt first, ForwardIt last, const T &value);

template <class InputIt, class UnaryPredicate>

InputIt find_if(InputIt first, InputIt last, (until C++ 20)

                                                 UnaryPredicate p);

template <class InputIt, class UnaryPredicate>

constexpr InputIt find_if(InputIt first, InputIt last, (since C++ 20)

                                                           UnaryPredicate p);
(1)

    template <class ExecutionPolicy, class ForwardIt, class UnaryPredicate>

    ForwardIt find_if(ExecutionPolicy &&policy, ForwardIt first, ForwardIt last, (4)(since C++ 17)

                                                                                     UnaryPredicate p);
(3)

    template <class InputIt, class UnaryPredicate>
    (since C++ 11)

        InputIt find_if_not(InputIt first, InputIt last, (until C++ 20)

                                                             UnaryPredicate q);

template <class InputIt, class UnaryPredicate>

constexpr InputIt find_if_not(InputIt first, InputIt last, (5)(since C++ 20)

                                                               UnaryPredicate q);

template <class ExecutionPolicy, class ForwardIt, class UnaryPredicate>

ForwardIt find_if_not(ExecutionPolicy &&policy, ForwardIt first, ForwardIt last, (6)(since C++ 17)

                                                                                     UnaryPredicate q);

Returns the first element in the range [first, last) that satisfies specific criteria:
1) find searches for an element equal to value
3) find_if searches for an element for which predicate p returns true
5) 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. This overload only participates in overload resolution if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

Parameters

first, last – the range of elements to examine
value – value to compare the elements to
policy – the execution policy to use. See execution_policy for details.
              unary predicate which returns true for the required element.
p – The expression p(v) must be convertible to bool for every argument v of type (possibly const) VT, where VT is the value type of InputIt, regardless of value_category, and must not modify v. Thus, a parameter type of VT&is not allowed
              , nor is VT unless for VT a move is equivalent to a copy
              (since C++11).
              unary predicate which returns false for the required element.
q – The expression q(v) must be convertible to bool for every argument v of type (possibly const) VT, where VT is the value type of InputIt, regardless of value_category, and must not modify v. Thus, a parameter type of VT&is not allowed
              , nor is VT unless for VT a move is equivalent to a copy
              (since C++11).

Type requirements

–
InputIt must meet the requirements of LegacyInputIterator.
–
ForwardIt must meet the requirements of LegacyForwardIterator.
–
UnaryPredicate must meet the requirements of Predicate.

Return value

Iterator to the first element satisfying the condition or last if no such element is found.

Complexity

At most last – first applications of the predicate

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.

Possible implementation

First version

  template<class InputIt, class T>
  constexpr 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>
  constexpr 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>
  constexpr InputIt find_if_not(InputIt first, InputIt last, UnaryPredicate q)
  {
      for (; first != last; ++first) {
          if (!q(*first)) {
              return first;
          }
      }
      return last;
  }

Notes

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));
}

Example

The following example finds an integer in a vector of integers.
// Run this code

#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

std::find_if_not (3) Linux Manual Page