std::not1

 

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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::unary_negate<Predicate> not1(const Predicate& pred );		(until C++14)
template<class Predicate > constexprstd::unary_negate<Predicate> not1(const Predicate& pred );		(since C++14) (deprecated in C++17) (removed in C++20)

std::not1 is a helper function to create a function object that returns the complement of the unary predicate function passed. The function object created is of type std::unary_negate<Predicate>.

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.

Parameters

pred

-

unary predicate

Return value

std::not1 returns an object of type std::unary_negate<Predicate>, constructed with pred.

Exceptions

(none)

Example

Run this code

#include <algorithm>#include <functional>#include <iostream>#include <iterator>#include <numeric>#include <vector>   struct LessThan7 :std::unary_function<int, bool>{bool operator()(int i)const{return i <7;}};   int main(){std::vector<int> v(10);std::iota(std::begin(v), std::end(v), 0);   std::cout<<std::count_if(begin(v), end(v), std::not1(LessThan7()))<<'\n';   // the same as above using std::functionstd::function<bool(int)> less_than_9 =[](int x){return x <9;};std::cout<<std::count_if(begin(v), end(v), std::not1(less_than_9))<<'\n';}

Output:

3 1

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)
unary_negate (deprecated in C++17)(removed in C++20)	wrapper function object returning the complement of the unary 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)
not2 (deprecated in C++17)(removed in C++20)	constructs custom std::binary_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)
unary_function (deprecated in C++11)(removed in C++17)	adaptor-compatible unary function base class (class template)