std::rel_ops::operator!=,>,<=,>=
Defined in header <utility>
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template< class T > bool operator!=( const T& lhs, const T& rhs ); |
(1) | (deprecated in C++20) |
template< class T > bool operator>( const T& lhs, const T& rhs ); |
(2) | (deprecated in C++20) |
template< class T > bool operator<=( const T& lhs, const T& rhs ); |
(3) | (deprecated in C++20) |
template< class T > bool operator>=( const T& lhs, const T& rhs ); |
(4) | (deprecated in C++20) |
Given a user-defined operator== and operator< for objects of type T
, implements the usual semantics of other comparison operators.
1) Implements operator!= in terms of operator==.
2) Implements operator> in terms of operator<.
3) Implements operator<= in terms of operator<.
4) Implements operator>= in terms of operator<.
Parameters
lhs | - | left-hand argument |
rhs | - | right-hand argument |
Return value
1) Returns true if lhs
is not equal to rhs
.
2) Returns true if lhs
is greater than rhs
.
3) Returns true if lhs
is less or equal to rhs
.
4) Returns true if lhs
is greater or equal to rhs
.
Possible implementation
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); } } |
Notes
Boost.operators provides a more versatile alternative to std::rel_ops
As of C++20, std::rel_ops
are deprecated in favor of operator<=>.
Example
Run this code
#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? : " << (f1 != f2) << '\n'; std::cout << "greater? : " << (f1 > f2) << '\n'; std::cout << "less equal? : " << (f1 <= f2) << '\n'; std::cout << "greater equal? : " << (f1 >= f2) << '\n'; }
Output:
not equal? : true greater? : false less equal? : true greater equal? : false