c-search-backward-char-property is a Lisp macro in `cc-defs.el'.

(c-search-backward-char-property PROPERTY VALUE &optional LIMIT)

Search backward for a text-property PROPERTY having value VALUE.
LIMIT bounds the search. The comparison is done with `equal'.

Leave point just before the character, set the match data on this
character, and return point. If VALUE isn't found, Return nil;
point is then left undefined.