| 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.
Member types
| Type | Definition |
|---|---|
argument_type | Predicate::argument_type |
result_type | bool |
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).
Example
#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
See also
| wrapper function object returning the complement of the binary predicate it holds (class template) | |
| (C++11) | wraps callable object of any type with specified function call signature (class template) |
constructs custom std::unary_negate object (function template) | |
| (until C++17) | creates an adaptor-compatible function object wrapper from a pointer to function (function template) |
| (until C++17) | adaptor-compatible unary function base class (class template) |
Please login to continue.