Print Unicode characters in C, using ncurses

I have to draw a box in C, using ncurses;

First, I have defined some values for simplicity:

#define RB "\e(0\x6a\e(B"  (ASCII 188,Right bottom, for example)

I have compiled with gcc, over Ubuntu, with -finput-charset=UTF-8 flag.

But, if I try to print with addstr or printw, I get the hexa code. What I`m doing wrong?