SDL_TTF: How to verify whether a Character is supported by the Font?

I’m using 2 fonts in my SDL_TTF (unicode) routines. If a character has a value greater than one byte I use the 2nd font. Now I want to change it to:
If the character is not available in 1st font (i.e. showing a box) I will use the 2nd font. But I don’t know how to do a test on a character for the 1st font. Anyone can help?