# std::unexpected_handler

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< cpp‎ | error

Defined in header `<exception>` |  |
typedef void (*unexpected_handler)(); |  | (until C++17) (deprecated since C++11)

`std::unexpected_handler` is the function pointer type (pointer to function that takes no arguments and returns void), which is installed and queried by the functions std::set_unexpected and std::get_unexpected and called by std::unexpected.

The C++ implementation provides a default `std::unexpected_handler` function, which calls std::terminate(). If the null pointer value is installed (by means of std::set_unexpected), the implementation may restore the default handler instead.

A user-defined `std::unexpected_handler` is expected to either terminate the program or throw an exception. If it throws an exception, one of the following three situations may be encountered:

1) the exception thrown by `std::unexpected_handler` satisfies the dynamic exception specification that was violated earlier. The new exception is allowed to escape the function and stack unwinding continues.

2) the exception thrown by `std::unexpected_handler` still violates the exception specification:

2a) however, the exception specification allows std::bad_exception: the thrown exception object is destroyed, and std::bad_exception is constructed by the C++ runtime and thrown instead.

2b) the exception specification does not allow std::bad_exception: std::terminate() is called.

### See also

unexpected (until C++17) | function called when dynamic exception specification is violated (function)
set_unexpected (until C++17) | changes the function to be called by std::unexpected (function)
get_unexpected (C++11)(until C++17) | obtains the current unexpected_handler (function)

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