| Defined in header <functional> | ||
|---|---|---|
template< class Predicate > std::binary_negate<Predicate> not2(const Predicate& pred); | (until C++14) | |
template< class Predicate > constexpr std::binary_negate<Predicate> not2(const Predicate& pred); | (since C++14) |
not2 is a helper function to create a function object that returns the complement of the binary predicate function passed. The function object created is of type std::binary_negate<Predicate>.
The binary predicate type must define two member types, first_argument_type and second_argument_type, that are convertible to the predicate's parameter types. The function objects obtained from std::owner_less, std::ref, std::cref, std::plus, std::minus, std::multiplies, std::divides, std::modulus, std::equal_to, std::not_equal_to, std::greater, std::less, std::greater_equal, std::less_equal, std::logical_not, std::logical_or, std::bit_and, std::bit_or, std::bit_xor, std::mem_fn, std::map::value_comp, std::multimap::value_comp, std::function, or from another call to std::not2 have these types defined, as are function objects derived from the deprecated std::binary_function.
Parameters
| pred | - | binary predicate |
Return value
std::not2 returns an object of type std::binary_negate<Predicate>, constructed with pred.
Exceptions
None.
Example
#include <algorithm>
#include <functional>
#include <iostream>
#include <vector>
struct old_same : std::binary_function<int, int, bool>
{
bool operator()(int a, int b) const { return a == b; }
};
struct new_same
{
bool operator()(int a, int b) const { return a == b; }
};
bool same_fn(int a, int b)
{
return a == b;
}
int main()
{
std::vector<int> v1{0, 1, 2};
std::vector<int> v2{2, 1, 0};
std::vector<bool> v3(v1.size());
std::cout << "negating a binary_function:\n";
std::transform(v1.begin(), v1.end(), v2.begin(), v3.begin(),
std::not2(old_same()));
std::cout << std::boolalpha;
for (std::size_t i = 0; i < v1.size(); ++i)
std::cout << v1[i] << ' ' << v2[i] << ' ' << v3[i] << '\n';
std::cout << "negating a standard functor:\n";
std::transform(v1.begin(), v1.end(), v2.begin(), v3.begin(),
std::not2(std::equal_to<int>()));
for (std::size_t i = 0; i < v1.size(); ++i)
std::cout << v1[i] << ' ' << v2[i] << ' ' << v3[i] << '\n';
std::cout << "negating a std::function:\n";
std::transform(v1.begin(), v1.end(), v2.begin(), v3.begin(),
std::not2(std::function<bool(int,int)>(new_same())));
for (std::size_t i = 0; i < v1.size(); ++i)
std::cout << v1[i] << ' ' << v2[i] << ' ' << v3[i] << '\n';
std::cout << "negating a std::reference_wrapper:\n";
std::transform(v1.begin(), v1.end(), v2.begin(), v3.begin(),
std::not2(std::ref(same_fn)));
for (std::size_t i = 0; i < v1.size(); ++i)
std::cout << v1[i] << ' ' << v2[i] << ' ' << v3[i] << '\n';
}Output:
negating a binary_function: 0 2 true 1 1 false 2 0 true negating a standard functor: 0 2 true 1 1 false 2 0 true negating a std::function: 0 2 true 1 1 false 2 0 true negating a std::reference_wrapper: 0 2 true 1 1 false 2 0 true
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 binary function base class (class template) |
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