mruby-mruby/doc/api/mruby/string.h.md

mrb_str_plus

   mrb_value mrb_str_plus(mrb_state*, mrb_value, mrb_value);

Adds to strings together.

mrb_ptr_to_str

   mrb_value mrb_ptr_to_str(mrb_state *, void*);

Converts pointer into a Ruby string.