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### is_signed

    template <class T>
    struct is_signed : public true_type-or-false_type {};

Inherits: If T is an signed integer type or an enumerated type with an underlying signed integer type, then inherits from true_type, otherwise inherits from false_type.

C++ Standard Reference: 3.9.1, 7.2.

Header: `#include <boost/type_traits/is_signed.hpp>` or `#include <boost/type_traits.hpp>`

Examples:

> `is_signed<int>` inherits from `true_type`.

> `is_signed<int const volatile>::type` is the type `true_type`.

> `is_signed<unsigned int>::value` is an integral constant expression that evaluates to false.

> `is_signed<myclass>::value` is an integral constant expression that evaluates to false.

> `is_signed<char>::value` is an integral constant expression whose value depends upon the signedness of type `char`.

> `is_signed<long long>::value` is an integral constant expression that evaluates to true.

> `is_signed<T>::value_type` is the type `bool`.