Namespaces
Variants
Views
Actions

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

From cppreference.com
< cpp‎ | utility‎ | tuple
Revision as of 16:55, 1 July 2013 by P12bot (Talk | contribs)

Defined in header <tuple>
template< class... TTypes, class... UTypes >

bool operator==( const tuple<TTypes...>& lhs,

                 const tuple<UTypes...>& rhs );
(1) (since C++11)
template< class... TTypes, class... UTypes >

bool operator!=( const tuple<TTypes...>& lhs,

                 const tuple<UTypes...>& rhs );
(2) (since C++11)
template< class... TTypes, class... UTypes >

bool operator<( const tuple<TTypes...>& lhs,

                const tuple<UTypes...>& rhs );
(3) (since C++11)
template< class... TTypes, class... UTypes >

bool operator<=( const tuple<TTypes...>& lhs,

                 const tuple<UTypes...>& rhs );
(5) (since C++11)
template< class... TTypes, class... UTypes >

bool operator>( const tuple<TTypes...>& lhs,

                const tuple<UTypes...>& rhs );
(4) (since C++11)
template< class... TTypes, class... UTypes >

bool operator>=( const tuple<TTypes...>& lhs,

                 const tuple<UTypes...>& rhs );
(6) (since C++11)

1-2) Compares every element of the tuple lhs with the corresponding element of the tuple rhs.

3-6) Compares lhs and rhs lexicographically, that is, compares the first elements, if they are equivalent, compares the second elements, if those are equivalent, compares the third elements, and so on.

All comparison operators are short-circuited; they do not access tuple elements beyond what is necessary to determine the result of the comparison.

Contents

Parameters

lhs, rhs - tuples to compare

Return value

1) true if std::get<i>(lhs) == std::get<i>(rhs) for all i in [0, sizeof...(Types)), otherwise false. For two empty tuples returns true.

2) !(lhs == rhs)

3) (bool)(std::get<0>(lhs) < std::get<0>(rhs)) || (!(bool)(std::get<0>(rhs) < std::get<0>(lhs)) && lhstail < rhstail), where lhstail is lhs without its first element, and rhstail is rhs without its first element. For two empty tuples, returns false.

4) !(lhs < rhs)

5) rhs < lhs

6) !(rhs < lhs)

Example

Because operator< is defined for tuples, containers of tuples can be sorted.

#include <iostream>
#include <tuple>
#include <vector>
#include <algorithm>
int main()
{
    std::vector<std::tuple<int, std::string, float>> v;
    v.emplace_back(2, "baz", -0.1);
    v.emplace_back(2, "bar", 3.14);
    v.emplace_back(1, "foo", 100.1);
    std::sort(v.begin(), v.end());
 
    for(auto p: v) {
        std::cout << "(" << std::get<0>(p) << ", " << std::get<1>(p)
                  << ", " << std::get<2>(p) << ")\n";
    }
}

Output:

(1, foo, 100.1)
(2, bar, 3.14)
(2, baz, -0.1)

See also