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# std::unary_negate

From cppreference.com
< cpp‎ | utility‎ | functional

Defined in header `<functional>` |  |
template< class Predicate > struct unary_negate : public std::unary_function<Predicate::argument_type, bool>; |  | (until C++11)
template< class Predicate > struct unary_negate; |  | (since C++11)

`unary_negate` is a wrapper function object returning the complement of the unary predicate it holds.

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.

`unary_negate` objects are easily constructed with helper function std::not1.

### [edit] Member types

Type | Definition
`argument_type` | Predicate::argument_type
`result_type` | bool

### [edit] Member functions

(constructor) | constructs a new unary_negate object with the supplied predicate (public member function)
operator() | returns the logical complement of the result of a call to the stored predicate (public member function)

## std::unary_negate::unary_negate

explicit unary_negate( Predicate const& pred ); |  | (until C++14)
explicit constexpr unary_negate( Predicate const& pred ); |  | (since C++14)

Constructs a `unary_negate` function object with the stored predicate `pred`.

### Parameters

pred | - | predicate function object

## std::unary_negate::operator()

bool operator()( argument_type const& x ) const; |  | (until C++14)
constexpr bool operator()( argument_type const& x ) const; |  | (since C++14)

Returns the logical complement of the result of calling pred(x).

### Parameters

x | - | argument to pass through to predicate

### Return value

The logical complement of the result of calling pred(x).

### [edit] Example

Run this code

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

    struct less_than_7 : std::unary_function<int, bool>
    {
        bool operator()(int i) const { return i < 7; }
    };

    int main()
    {
        std::vector<int> v;
        for (int i = 0; i < 10; ++i) v.push_back(i);

        std::unary_negate<less_than_7> not_less_than_7((less_than_7()));

        std::cout << std::count_if(v.begin(), v.end(), not_less_than_7);

        /* C++11 solution:
            // Use std::function<bool (int)>
            std::function<bool (int)> not_less_than_7 =
                [](int x)->bool{ return !less_than_7()(x); };

            std::cout << std::count_if(v.begin(), v.end(), not_less_than_7);
        */
    }

Output:

    3

### [edit] See also

binary_negate | wrapper function object returning the complement of the binary predicate it holds (class template) [edit]
function (C++11) | wraps callable object of any type with specified function call signature (class template) [edit]
not1 | constructs custom std::unary_negate object (function template) [edit]
ptr_fun (until C++17) | creates an adaptor-compatible function object wrapper from a pointer to function (function template) [edit]
unary_function (until C++17) | adaptor-compatible unary function base class (class template) [edit]

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