operator==, !=, <, <=, >, >=(std::variant) - cppreference.com

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# operator==, !=, <, <=, >, >=(std::variant)

From cppreference.com
< cpp‎ | utility‎ | variant

Defined in header `<variant>` |  |
template <class... Types> constexpr bool operator==(const std::variant<Types...>& v, const std::variant<Types...>& w); | (1) | (since C++17)
template <class... Types> constexpr bool operator!=(const std::variant<Types...>& v, const std::variant<Types...>& w); | (2) | (since C++17)
template <class... Types> constexpr bool operator<(const std::variant<Types...>& v, const std::variant<Types...>& w); | (3) | (since C++17)
template <class... Types> constexpr bool operator>(const std::variant<Types...>& v, const std::variant<Types...>& w); | (4) | (since C++17)
template <class... Types> constexpr bool operator<=(const std::variant<Types...>& v, const std::variant<Types...>& w); | (5) | (since C++17)
template <class... Types> constexpr bool operator>=(const std::variant<Types...>& v, const std::variant<Types...>& w); | (6) | (since C++17)

1) Equality operator for variants:

- If v.index() != w.index(), returns `false`;
- otherwise if v.valueless_by_exception(), returns `true`;
- otherwise returns std::get<v.index()>(v) == std::get<v.index()>(w). The behavior is undefined if std::get<i>(v) == std::get<i>(w) is not a valid expression returning a type convertible to bool, for any `i`.

2) Inequality operator for variants:

- If v.index() != w.index(), returns `true`;
- otherwise if v.valueless_by_exception(), returns `false`;
- otherwise returns std::get<v.index()>(v) != std::get<v.index()>(w). The behavior is undefined if std::get<i>(v) != std::get<i>(w) is not a valid expression returning a type convertible to bool, for any `i`.

3) Less-than operator for variants:

- If w.valueless_by_exception(), returns `false`;
- otherwise if v.valueless_by_exception(), returns `true`;
- otherwise if v.index() < w.index(), returns `true`;
- otherwise if v.index() > w.index(), returns `false`;
- otherwise returns std::get<v.index()>(v) < std::get<v.index()>(w). The behavior is undefined if std::get<i>(v) < std::get<i>(w) is not a valid expression returning a type convertible to bool, for any `i`.

4) Greater-than operator for variants:

- If v.valueless_by_exception(), returns `false`;
- otherwise if w.valueless_by_exception(), returns `true`;
- otherwise if v.index() > w.index(), returns `true`;
- otherwise if v.index() < w.index(), returns `false`;
- otherwise returns std::get<v.index()>(v) > std::get<v.index()>(w). The behavior is undefined if std::get<i>(v) > std::get<i>(w) is not a valid expression returning a type convertible to bool, for any `i`.

5) Less-equal operator for variants:

- If v.valueless_by_exception(), returns `true`;
- otherwise if w.valueless_by_exception(), returns `false`;
- otherwise if v.index() < w.index(), returns `true`;
- otherwise if v.index() > w.index(), returns `false`;
- otherwise returns std::get<v.index()>(v) <= std::get<v.index()>(w). The behavior is undefined if std::get<i>(v) <= std::get<i>(w) is not a valid expression returning a type convertible to bool, for any `i`.

6) Greater-equal operator for variants:

- If w.valueless_by_exception(), returns `true`;
- otherwise if v.valueless_by_exception(), returns `false`;
- otherwise if v.index() > w.index(), returns `true`;
- otherwise if v.index() < w.index(), returns `false`;
- otherwise std::get<v.index()>(v) >= std::get<v.index()>(w). The behavior is undefined if std::get<i>(v) >= std::get<i>(w) is not a valid expression returning a type convertible to bool, for any `i`.

### [edit] Parameters

v,w | - | variants to compare

### [edit] Return value

The boolean result of the comparison as described above.

### [edit] Example

| This section is incomplete Reason: no example

### [edit] See also

operator==operator!=operator<operator<=operator>operator>= (C++17) | compares `optional` objects (function template) [edit]

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