as for checking whether or not it is a function... each subroutine in C starts with one or more return type:

int, long, short, double, float, void, char, unsigned ...

then it has a single word for the function name (simply: \w+ )

then it will have an open parenthesis '(' followed eventually by a closed parenthesis ')' ....

and then there will be the opening bracket '{'

thats all you have to parse on to find that it is a function... of course be sure to ignore function "prototypes"... they will be distinguished by a semicolon ';' after the closing parenthesis

the problem for you will be that a function declaration can spread across multiple lines... very often that first opening bracket is on a line by itself. like so: