FcFreeTypeCharSetAndSpacing - compute Unicode coverage and spacing type
#include <fontconfig.h>
#include <fcfreetype.h>
FcCharSet * FcFreeTypeCharSetAndSpacing (FT_Face face, FcBlanks *blanks, int *spacing);
Scans a FreeType face and returns the set of encoded Unicode chars. FcBlanks is
  deprecated, blanks is ignored and accepted only for compatibility with
  older code. spacing receives the computed spacing type of the font, one
  of FC_MONO for a font where all glyphs have the same width, FC_DUAL, where the
  font has glyphs in precisely two widths, one twice as wide as the other, or
  FC_PROPORTIONAL where the font has glyphs of many widths.