# Matches C/C++ #define 
(?m)\#\s{0,}
define                             #  Match the define
\s+                                # Whitespace
(?<Identifier>\w+)                 # The identifier
\s{0,}                             # Optional Whitespace
# Then either
(?>(?<Definition>([^\\]+$          # A Line with no escape OR
|(?<Line>[^\\]+?\\(?=(?>\r\n|\n))) # One or more lines ending with \
{1,})))