write_json fails when using basic_ptree with other string types

[ghost]

Good morning,

I was working on a project, I would like to use basic_ptree with strings of non standard type (see T1.cpp attached toy example).

While read_json works smootly, write_json fails (see compiler output T1.error.txt).

I checked the code and, apparently, an easy fix could enable this feature (see write.hpp which I revised for your convenience, original lines of code are commented, those inserted are marked with an eol comment "suggested").

Thank you for your time,
Marco.

write.hpp.txt
T1.cpp.txt
T1.error.txt