# std::exception_ptr

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< cpp‎ | error

Defined in header `<exception>` |  |
using exception_ptr = /*unspecified*/ |  | (since C++11)

`std::exception_ptr` is a nullable pointer-like type that manages an exception object which has been thrown and captured with std::current_exception. An instance of `std::exception_ptr` may be passed to another function, possibly on another thread, where the exception may be rethrown and handled with a catch clause.

A default-constructed `std::exception_ptr` is a null pointer; it does not point to an exception object.

Two instances of `std::exception_ptr` compare equal only if they are both null or both point at the same exception object.

`std::exception_ptr` is not implicitly convertible to any arithmetic, enumeration, or pointer type. It is contextually convertible to bool, and will evaluate to false if it is null, true otherwise.

The exception object referenced by an `std::exception_ptr` remains valid as long as there remains at least one `std::exception_ptr` that is referencing it: `std::exception_ptr` is a shared-ownership smart pointer (note: this is in addition to the usual exception object lifetime rules).

`std::exception_ptr` meets the requirements of NullablePointer.

### Example

Run this code

    #include <exception>
    #include <iostream>
    #include <stdexcept>
    #include <string>

    void handle_eptr(std::exception_ptr eptr) // passing by value is OK
    {
        try
        {
            if (eptr)
                std::rethrow_exception(eptr);
        }
        catch(const std::exception& e)
        {
            std::cout << "Caught exception: '" << e.what() << "'\n";
        }
    }

    int main()
    {
        std::exception_ptr eptr;

        try
        {
            [[maybe_unused]]
            char ch = std::string().at(1); // this generates a std::out_of_range
        }
        catch(...)
        {
            eptr = std::current_exception(); // capture
        }

        handle_eptr(eptr);

    } // destructor for std::out_of_range called here, when the eptr is destructed

Possible output:

    Caught exception: 'basic_string::at: __n (which is 1) >= this->size() (which is 0)'

### See also

make_exception_ptr (C++11) | creates an std::exception_ptr from an exception object (function template)
current_exception (C++11) | captures the current exception in a std::exception_ptr (function)
rethrow_exception (C++11) | throws the exception from an std::exception_ptr (function)

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