std::not2

 

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unary_function (until C++17*) binary_function (until C++17*) ptr_fun (until C++17*) pointer_to_unary_function (until C++17*) pointer_to_binary_function (until C++17*)   mem_fun (until C++17*) mem_fun_tmem_fun1_tconst_mem_fun_tconst_mem_fun1_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) not1 (until C++20*) not2 (until C++20*)	binder1stbinder2nd (until C++17*)(until C++17*) bind1stbind2nd (until C++17*)(until C++17*) mem_fun_ref (until C++17*) mem_fun_ref_tmem_fun1_ref_tconst_mem_fun_ref_tconst_mem_fun1_ref_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) unary_negate (until C++20*) binary_negate (until C++20*)

 

Defined in header <functional>
template<class Predicate > std::binary_negate<Predicate> not2(const Predicate& pred );		(until C++14)
template<class Predicate > constexprstd::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.

Parameters

pred

-

binary predicate

Return value

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

Exceptions

(none)

Example

Run this code

#include <algorithm>#include <cstddef>#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

not_fn (C++17)	creates a function object that returns the complement of the result of the function object it holds (function template)
binary_negate (deprecated in C++17)(removed in C++20)	wrapper function object returning the complement of the binary predicate it holds (class template)
function (C++11)	copyable wrapper of any copy constructible callable object (class template)
move_only_function (C++23)	move-only wrapper of any callable object that supports qualifiers in a given call signature (class template)
not1 (deprecated in C++17)(removed in C++20)	constructs custom std::unary_negate object (function template)
ptr_fun (deprecated in C++11)(removed in C++17)	creates an adaptor-compatible function object wrapper from a pointer to function (function template)
binary_function (deprecated in C++11)(removed in C++17)	adaptor-compatible binary function base class (class template)