functor_input example for multi_pass iterator has various issues

[Jeff Trull <edaskel@…>]

As given, the functor_input example in the multi_pass documentation (see "How to write a functor for use with the functor_input InputPolicy") will not compile, and once the compile issues are fixed, will not run successfully. The issues are more than simply typos - among them are:

1) operator() cannot be const, as it modifies the private member c_ 2) policies are given to multi_pass directly instead of through default_policy 3) the policies are in the wrong order (functor_input must be third, not first) 4) '\0' cannot be used as the EOF marker, because the multi_pass is_eof() member will return true in this case due to a comparison against the initialized curtok value of 0 - this may be a bug.

I have attached a modified version of the example which works as described in the documentation.

[Jeff Trull <edaskel@…>]

Suggested replacement code

[Hartmut Kaiser]

(In [82759]) Spirit: fix #7977: functor_input example for multi_pass iterator has various issues