...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
template <class Base, class Derived>
struct is_base_of : public true_type-or-false_type
{};
Inherits: If Base is base class of type Derived or if both types are the same then inherits from true_type, otherwise inherits from false_type.
This template will detect non-public base classes, and ambiguous base classes.
Note that is_base_of<X,X>
will always inherit from true_type.
This is the case even if X
is not a class type. This is a change in behaviour from Boost-1.33
in order to track the Technical Report on C++ Library Extensions.
Types Base
and Derived
must not be incomplete types.
C++ Standard Reference: 10.
Header: #include
<boost/type_traits/is_base_of.hpp>
or #include <boost/type_traits.hpp>
Compiler Compatibility: If the compiler
does not support partial-specialization of class templates, then this template
can not be used with function types. There are some older compilers which
will produce compiler errors if Base
is a private base class of Derived
,
or if Base
is an ambiguous
base of Derived
. These compilers
include Borland C++, older versions of Sun Forte C++, Digital Mars C++, and
older versions of EDG based compilers.
Examples:
Given:
class Base{}; class Derived : public Base{};
is_base_of<Base, Derived>
inherits fromtrue_type
.
is_base_of<Base, Derived>::type
is the typetrue_type
.
is_base_of<Base, Derived>::value
is an integral constant expression that evaluates to true.
is_base_of<Base, Base>::value
is an integral constant expression that evaluates to true: a class is regarded as it's own base.
is_base_of<T, T>::value_type
is the typebool
.