logical_not Struct

Article
01/02/2018

The latest version of this topic can be found at logical_not Struct.

A predefined function object that performs the logical not operation ( operator!) on its argument.

Syntax

template <class Type = void>
struct logical_not : public unary_function<Type, bool>  
{
    bool operator()(
    const Type& Left) const;

 };

// specialized transparent functor for operator!
template <>
struct logical_not<void>  
{
template <class Type>
auto operator()(Type&& Left) const
 ->  
decltype(!std::forward<Type>(Left));

 };

Parameters

Type
Any type that supports an operator! that takes an operand of the specified or inferred type.

Left
The operand of the logical not operation. The unspecialized template takes an lvalue reference argument of type Type. The specialized template does perfect forwarding of lvalue and rvalue reference arguments of inferred type Type.

Return Value

The result of !``Left. The specialized template does perfect forwarding of the result, which has the type that's returned by operator!.

Example

// functional_logical_not.cpp  
// compile with: /EHsc  
#include <deque>  
#include <algorithm>  
#include <functional>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;  
   deque<bool> d1, d2 ( 7 );  
   deque<bool>::iterator iter1, iter2;  
  
   int i;  
   for ( i = 0 ; i < 7 ; i++ )  
   {  
      d1.push_back((bool)((i % 2) != 0));  
   }  
  
   cout << boolalpha;    // boolalpha I/O flag on  
  
   cout << "Original deque:\n d1 = ( " ;  
   for ( iter1 = d1.begin( ) ; iter1 != d1.end( ) ; iter1++ )  
      cout << *iter1 << " ";  
   cout << ")" << endl;  
  
   // To flip all the truth values of the elements,  
   // use the logical_not function object  
   transform( d1.begin( ), d1.end( ), d2.begin( ),logical_not<bool>( ) );  
   cout << "The deque with its values negated is:\n d2 = ( " ;  
   for ( iter2 = d2.begin( ) ; iter2 != d2.end( ) ; iter2++ )  
      cout << *iter2 << " ";  
   cout << ")" << endl;  
}  
/* Output:  
Original deque:  
 d1 = ( false true false true false true false )  
The deque with its values negated is:  
 d2 = ( true false true false true false true )  
 */

Requirements

Header: <functional>

Namespace: std

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