What's the proper way to get cchar_t?

[Pierre Abbat]

I'm writing an ncurses program which computes the volume of a cylindrical 
shell. I'm using Unicode, so I want wide characters. I defined 
_XOPEN_SOURCE_EXTENDED so that I could get cchar_t, but then the preprocessor 
didn't know what M_PI is. I undefined it, and got it to run where some files 
were compiled with -D_XOPEN_SOURCE_EXTENDED and some without, but then I 
edited another source file and now it doesn't know what cchar_t is. How do I 
fix this?

Pierre