std::unary_negate - cppreference.com (original) (raw)

| Defined in header | | | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | ------------------------------------------------------ | | 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) (deprecated in C++17) (removed in C++20) |

std::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.

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

Contents

• 1 Member types
• 2 Member functions
• 3 std::unary_negate::unary_negate
  • 3.1 Parameters
• 4 std::unary_negate::operator()
  • 4.1 Parameters
  • 4.2 Return value
  • 4.3 Example
  • 4.4 See also

[edit] Member types

[edit] Member functions

| | constructs a new unary_negate object with the supplied predicate (public member function) | | ---------------------------------------------------------------------------------------------------------- | | | 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) | | ---------------------------------------------------------- | | ------------- | | constexpr explicit unary_negate( Predicate const& pred ); | | (since C++14) |

Constructs a std::unary_negate function object with the stored predicate pred.

Parameters

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

Return value

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

[edit] Example

#include #include #include #include   struct less_than_7 : std::unary_function<int, bool> { bool operator()(int i) const { return i < 7; } };   int main() { std::vector v(7, 7); v[0] = v[1] = v[2] = 6;   std::unary_negate not_less_than_7((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:

[edit] See also