# std::not1

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< cpp‎ | utility‎ | functional

Defined in header `<functional>` |  |
template< class Predicate > std::unary_negate<Predicate> not1( const Predicate& pred ); |  | (until C++14)
template< class Predicate > constexpr std::unary_negate<Predicate> not1( const Predicate& pred ); |  | (since C++14) (deprecated in C++17) (removed in C++20)

`std::not1` is a helper function to create a function object that returns the complement of the unary predicate function passed. The function object created is of type std::unary_negate<Predicate>.

The unary predicate type must define a member type, `argument_type`, that is convertible to the predicate's parameter type. The unary function objects obtained from std::ref, std::cref, std::negate, std::logical_not, std::mem_fn, std::function, std::hash, or from another call to std::not1 have this type defined, as are function objects derived from the deprecated std::unary_function.

### Parameters

pred | - | unary predicate

### Return value

`std::not1` returns an object of type std::unary_negate<Predicate>, constructed with pred.

### Exceptions

None.

### Example

Run this code

    #include <algorithm>
    #include <functional>
    #include <iostream>
    #include <iterator>
    #include <numeric>
    #include <vector>

    struct LessThan7 : std::unary_function<int, bool>
    {
        bool operator()(int i) const { return i < 7; }
    };

    int main()
    {
        std::vector<int> v(10);
        std::iota(begin(v), end(v), 0);

        std::cout << std::count_if(begin(v), end(v), std::not1(LessThan7())) << '\n';

        //same as above, but using `std::function`
        std::function<bool(int)> less_than_9 = [](int x) { return x < 9; };
        std::cout << std::count_if(begin(v), end(v), std::not1(less_than_9)) << '\n';
    }

Output:

    3
    1

### See also

not_fn (C++17) | creates a function object that returns the complement of the result of the function object it holds (function template)
unary_negate (deprecated in C++17)(removed in C++20) | wrapper function object returning the complement of the unary predicate it holds (class template)
function (C++11) | wraps callable object of any copy constructible type with specified function call signature (class template)
move_only_function (C++23) | wraps callable object of any type with specified function call signature (class template)
not2 (deprecated in C++17)(removed in C++20) | constructs custom std::binary_negate object (function template)
ptr_fun (deprecated in C++11)(removed in C++17) | creates an adaptor-compatible function object wrapper from a pointer to function (function template)
unary_function (deprecated in C++11)(removed in C++17) | adaptor-compatible unary function base class (class template)

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