[except.nested] (original) (raw)

17 Language support library [support]

17.9 Exception handling [support.exception]

17.9.8 nested_exception [except.nested]

namespace std { class nested_exception { public: constexpr nested_exception() noexcept;constexpr nested_exception(const nested_exception&) noexcept = default;constexpr nested_exception& operator=(const nested_exception&) noexcept = default;constexpr virtual ~nested_exception() = default;[[noreturn]] constexpr void rethrow_nested() const;constexpr exception_ptr nested_ptr() const noexcept;};template<class T> [[noreturn]] constexpr void throw_with_nested(T&& t);template<class E> constexpr void rethrow_if_nested(const E& e);}

The class nested_exception is designed for use as a mixin through multiple inheritance.

It captures the currently handled exception and stores it for later use.

[Note 1:

nested_exception has a virtual destructor to make it a polymorphic class.

Its presence can be tested for with dynamic_cast.

— _end note_]

constexpr nested_exception() noexcept;

Effects: The constructor calls current_exception() and stores the returned value.

[[noreturn]] constexpr void rethrow_nested() const;

Effects: If nested_ptr() returns a null pointer, the function calls the function std​::​terminate.

Otherwise, it throws the stored exception captured by *this.

constexpr exception_ptr nested_ptr() const noexcept;

Returns: The stored exception captured by this nested_exception object.

template<class T> [[noreturn]] constexpr void throw_with_nested(T&& t);

Throws: If is_class_v<U> && !is_final_v<U> && !is_base_of_v<nested_exception, U>is true, an exception of unspecified type that is publicly derived from bothU and nested_exceptionand constructed from std​::​forward<T>(t), otherwisestd​::​forward<T>(t).

template<class E> constexpr void rethrow_if_nested(const E& e);

Effects: If E is not a polymorphic class type, or if nested_exception is an inaccessible or ambiguous base class of E, there is no effect.

Otherwise, performs:if (auto p = dynamic_cast<const nested_exception*>(addressof(e))) p->rethrow_nested();