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std::rel_ops::operator!=,>,<=,>=

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C++
 
Utilità libreria
Tipo di supporto (basic types, RTTI, type traits)
Gestione della memoria dinamica
La gestione degli errori
Programma di utilità
Funzioni variadic
Data e ora
Funzione oggetti
initializer_list(C++11)
bitset
hash(C++11)
Gli operatori relazionali
Original:
Relational operators
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rel_ops::operator!=
rel_ops::operator>
rel_ops::operator<=
rel_ops::operator>=
Coppie e tuple
Original:
Pairs and tuples
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pair
tuple(C++11)
piecewise_construct_t(C++11)
piecewise_construct(C++11)
Swap, in avanti e spostare
Original:
Swap, forward and move
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swap
forward(C++11)
move(C++11)
move_if_noexcept(C++11)
declval(C++11)
 
Elemento definito nell'header <utility>
template< class T >
bool operator!=( const T& lhs, const T& rhs );
 (1)
template< class T >
bool operator>( const T& lhs, const T& rhs );
 (2)
template< class T >
bool operator<=( const T& lhs, const T& rhs );
 (3)
template< class T >
bool operator>=( const T& lhs, const T& rhs );
 (4)
Dato un definito dall'utente operator== operator< e per gli oggetti di tipo T, implementa la semantica abituali di altri operatori di confronto.
Original:
Given a user-defined operator== and operator< for objects of type T, implements the usual semantics of other comparison operators.
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1)
Implementa operator!= in termini di operator==.
Original:
Implements operator!= in terms of operator==.
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2)
Implementa operator> in termini di operator<.
Original:
Implements operator> in terms of operator<.
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3)
Implementa operator<= in termini di operator<.
Original:
Implements operator<= in terms of operator<.
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4)
Implementa operator>= in termini di operator<.
Original:
Implements operator>= in terms of operator<.
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Indice

[modifica] Parametri

lhs -
sinistra argomento
Original:
left-hand argument
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rhs -
destra argomento
Original:
right-hand argument
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[modifica] Valore di ritorno

1)
Restituisce true se lhs è' non è uguale a rhs.
Original:
Returns true if lhs is not equal to rhs.
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2)
Restituisce true se lhs è superiore di rhs.
Original:
Returns true if lhs is greater than rhs.
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3)
Restituisce true se lhs' è minore o uguale a rhs.
Original:
Returns true if lhs is less or equal to rhs.
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4)
Restituisce true se lhs è maggiore o uguale a rhs.
Original:
Returns true if lhs is greater or equal to rhs.
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[modifica] Possibile implementazione

First version 
namespace rel_ops {
    template< class T >
    bool operator!=( const T& lhs, const T& rhs ) 
    {
        return !(lhs == rhs);
    }
}
Second version 
namespace rel_ops {
    template< class T >
    bool operator>( const T& lhs, const T& rhs ) 
    {
        return rhs < lhs;
    }
}
Third version 
namespace rel_ops {
    template< class T >
    bool operator<=( const T& lhs, const T& rhs ) 
    {
        return !(rhs < lhs);;
    }
}
Fourth version 
namespace rel_ops {
    template< class T >
    bool operator>=( const T& lhs, const T& rhs ) 
    {
        return !(lhs < rhs);
    }
}

[modifica] Esempio

#include <iostream>
#include <utility>
 
struct Foo {
    int n;
};
 
bool operator==(const Foo& lhs, const Foo& rhs)
{
    return lhs.n == rhs.n;
}
 
bool operator<(const Foo& lhs, const Foo& rhs)
{
    return lhs.n < rhs.n;
}
 
int main()
{
    Foo f1 = {1};
    Foo f2 = {2};
    using namespace std::rel_ops;
 
    std::cout << std::boolalpha;
    std::cout << "not equal?     : " << (bool) (f1 != f2) << '\n';
    std::cout << "greater?       : " << (bool) (f1 > f2) << '\n';
    std::cout << "less equal?    : " << (bool) (f1 <= f2) << '\n';
    std::cout << "greater equal? : " << (bool) (f1 >= f2) << '\n';
}

Output: 

not equal?     : true
greater?       : false
less equal?    : true
greater equal? : false
Estratto da "https://it.cppreference.com/mwiki/index.php?title=cpp/utility/rel_ops/operator_cmp&oldid=27238"