# Boost Exception

### exception_ptr

#include <boost/exception_ptr.hpp>

    namespace
    boost
        {
        typedef ---unspecified--- exception_ptr;
        }

The exception_ptr type can be used to refer to a copy of an exception object. It is Default Constructible, Copy Constructible, Assignable and Equality Comparable; exception_ptr's operations do not throw.

The referenced object remains valid at least as long as there is an exception_ptr object that refers to it.

Two instances of exception_ptr are equivalent and compare equal if and only if they refer to the same exception.

The default constructor of exception_ptr produces the null value of the type. The null value is equivalent only to itself.

#### Thread safety

- It is legal for multiple threads to hold exception_ptr references to the same exception object.
- It is illegal for multiple threads to modify the same exception_ptr object concurrently.
- While calling current_exception makes a copy of the current exception object, it is still possible for the two copies to share internal state. Therefore, in general it is not safe to call rethrow_exception concurrently to throw the same exception object into multiple threads.

#### Nesting of exceptions:

An exception_ptr can be added as error_info to any boost::exception. This is a convenient way to nest exceptions. There is no limit on the depth of the nesting, however cyclic references result in undefined behavior.

### See Also:

Boost Exception
boost/exception_ptr.hpp
copy_exception
current_exception
diagnostic_information
enable_current_exception
Frequently Asked Questions
original_exception_type
rethrow_exception
unknown_exception