# std::ios_base::event_callback

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< cpp‎ | io‎ | ios base

typedef void (*event_callback)(event type, ios_base& ios, int index); |  |

The type of function callbacks that can be registered using register_callback() to be called on specific events.

`type` is a value of type `ios_base::event` which indicates the type of the event that will invoke this callback.

`ios` refers to the stream object for which the callback is invoked: *this is passed as the argument when callbacks are invoked by std::ios_base and std::basic_ios member functions.

`index` is the user-provided value passed to register_callback() when registering the function.

### See also

copyfmt | copies formatting information (public member function of `std::basic_ios<CharT,Traits>`)
imbue | sets locale (public member function)
(destructor) [virtual] | destructs the object (virtual public member function)
register_callback | registers event callback function (public member function)

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