c-literal-type is a compiled Lisp function in `cc-engine.el'.

(c-literal-type RANGE)

Convenience function that given the result of `c-literal-limits',
returns nil or the type of literal that the range surrounds, one
of the symbols 'c, 'c++ or 'string. It's much faster than using
`c-in-literal' and is intended to be used when you need both the
type of a literal and its limits.

Note that this function might do hidden buffer changes. See the
comment at the start of cc-engine.el for more info.