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

(c-in-literal &optional LIM DETECT-CPP)

Return the type of literal point is in, if any.
The return value is `c' if in a C-style comment, `c++' if in a C++
style comment, `string' if in a string literal, `pound' if DETECT-CPP
is non-nil and in a preprocessor line, or nil if somewhere else.
Optional LIM is used as the backward limit of the search. If omitted,
or nil, `c-beginning-of-defun' is used.

The last point calculated is cached if the cache is enabled, i.e. if
`c-in-literal-cache' is bound to a two element vector.

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