A program can register a callback function on a particular stream as follows:
// Callback function
void show_event(ios_base::event e, iosbase& io, int index)
{
if (e == ios_base::imbue_event)
cout << "imbue called" << endl;
else if (e == ios_base::erase_event)
cout << "stream destroyed" << endl;
else
cout << "cpyfmt called" << endl;
}
ostringstream s;
s.register_callback(my_callback,0); //1
s.imbue(locale::global()); //2
| //1 | The function show_event will now be called with either ios_base::erase_event, ios_base::imbue_event, or ios_base::copyfmt_event as the first argument, depending on whether the destruction of the stream, the imbuing of a new locale, or a call to cpyfmt initiated the callback. |
| //2 | This causes show_event to be called. The first argument is ios_base::imbue_event; the second argument is a reference to the stream where the event occurred, which is s in this case; and the third argument is always the index provided in the call to register_callback, which is 0 in this case.
If more than one function is registered, functions will be called in the opposite order of registration. |
Please refer to Section 5.9.2 for an extensive example using callback functions with a user-defined stream inserter.
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