std::not2 - cppreference.com (original) (raw)

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

std::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.

[edit] Parameters

[edit] Return value

std::not2 returns an object of type std::binary_negate<Predicate>, constructed with pred.

[edit] Exceptions

(none)

[edit] Example

#include #include #include #include #include   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 v1{0, 1, 2}; std::vector v2{2, 1, 0}; std::vector 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()));   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

[edit] See also