Ostringstream

I was converting the PFR corpus into my XML style. I must change them into utf8 code. But the output function was complicated. As learned in C++ Primer, I tried to use the ostringstream.

Formaly, I believed the ostringstream is a derive of string class. So I used clear method for clearing the content of the string. But that could not run correctly.

I don't know how to modifiy my program. The single solution is asking in CSDN.