W3cubDocs

/C++

operator==,!=,<,<=,>,>=(std::valarray)

Defined in header <valarray> 
template< class T > 
std::valarray<bool> operator==( const std::valarray<T>& lhs, const std::valarray<T>& rhs );
template< class T > 
std::valarray<bool> operator!=( const std::valarray<T>& lhs, const std::valarray<T>& rhs );
template< class T > 
std::valarray<bool> operator< ( const std::valarray<T>& lhs, const std::valarray<T>& rhs );
template< class T > 
std::valarray<bool> operator<=( const std::valarray<T>& lhs, const std::valarray<T>& rhs );
template< class T > 
std::valarray<bool> operator> ( const std::valarray<T>& lhs, const std::valarray<T>& rhs );
template< class T > 
std::valarray<bool> operator>=( const std::valarray<T>& lhs, const std::valarray<T>& rhs );
 (1) 
template< class T > 
std::valarray<bool> operator==( const typename std::valarray<T>::value_type & lhsv,
                                const std::valarray<T>& rhs );
template< class T > 
std::valarray<bool> operator!=( const typename std::valarray<T>::value_type & lhsv,
                                const std::valarray<T>& rhs );
template< class T > 
std::valarray<bool> operator< ( const typename std::valarray<T>::value_type & lhsv,
                                const std::valarray<T>& rhs );
template< class T > 
std::valarray<bool> operator<=( const typename std::valarray<T>::value_type & lhsv,
                                const std::valarray<T>& rhs );
template< class T > 
std::valarray<bool> operator> ( const typename std::valarray<T>::value_type & lhsv,
                                const std::valarray<T>& rhs );
template< class T > 
std::valarray<bool> operator>=( const typename std::valarray<T>::value_type & lhsv,
                                const std::valarray<T>& rhs );
 (2) 
template< class T > 
std::valarray<bool> operator==( const std::valarray<T>& lhs,
                                const typename std::valarray<T>::value_type & rhsv );
template< class T > 
std::valarray<bool> operator!=( const std::valarray<T>& lhs,
                                const typename std::valarray<T>::value_type & rhsv );
template< class T > 
std::valarray<bool> operator< ( const std::valarray<T>& lhs,
                                const typename std::valarray<T>::value_type & rhsv );
template< class T > 
std::valarray<bool> operator<=( const std::valarray<T>& lhs,
                                const typename std::valarray<T>::value_type & rhsv );
template< class T > 
std::valarray<bool> operator> ( const std::valarray<T>& lhs,
                                const typename std::valarray<T>::value_type & rhsv );
template< class T > 
std::valarray<bool> operator>=( const std::valarray<T>& lhs,
                                const typename std::valarray<T>::value_type & rhsv );
 (3)

Compares each value within the numeric array with another value.

1) Returns a numeric array of bool containing elements each of which is obtained by applying the indicated comparison operator to the corresponding values of lhs and rhs.

The behavior is undefined if size() != v.size().

2) Returns a numeric array of bool containing elements each of which is obtained by applying the indicated comparison operator to lhsv and the corresponding value of rhs.
3) Returns a numeric array of bool containing elements each of which is obtained by applying the indicated comparison operator to the corresponding value of lhs and rhsv.

Parameters

lhs, rhs - numeric arrays to compare
lhsv, rhsv - values to compare to each element within a numeric array

Return value

A numeric array of bool containing comparison results of corresponding elements.

Exceptions

May throw implementation-defined exceptions.

Notes

Each of the operators can only be instantiated if the following requirements are met:

  • The indicated operator can be applied to type T.
  • The result value can be unambiguously converted to bool.

The function can be implemented with the return type different from std::valarray. In this case, the replacement type has the following properties:

Example

#include <iostream>
#include <valarray>
 
int main()
{
    // zero all negatives in a valarray
    std::valarray<int> v = {1, -1, 0, -3, 10, -1, -2};
    std::cout << "Before: ";
    for(auto n: v) {
        std::cout << n << ' ';
    }
    std::cout << '\n';
    v[v < 0] = 0;
    std::cout << "After: ";
    for(auto n: v) {
        std::cout << n << ' ';
    }
    std::cout << '\n';
 
    // convert the valarray<bool> result of == to a single bool
    std::valarray<int> a = {1,2,3};
    std::valarray<int> b = {2,4,6};
 
    std::cout << "2*a == b is " << std::boolalpha
              << (2*a == b).min() << '\n';
}

Output:

Before: 1 -1 0 -3 10 -1 -2
After: 1 0 0 0 10 0 0
2*a == b is true

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3074 C++98 T is deduced from both the scalar and the valarray for (2-3),
disallowing mixed-type calls 		only deduce T from the valarray

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/numeric/valarray/operator_cmp