Use double colons (::) in #define

Question

May I use double colons in #define ? I\'d like to save some writing in the implementation files, e.g. like this:

// foo.h
#define template templ         


        

Answer 1

No. The name of a macro must be an identifier; it can't consist of other characters and it can't consist of multiple tokens.

#define template is invalid because template is not an identifier, it is a keyword.

#define foo:: foo<T>:: was valid in C90 and C++98: it defines a macro named foo that is replaced by :: foo<T>:: (that's not what you want to do, but it was valid). However, this is invalid in C99 and C++11 because in the newer revisions of the languages, there must be whitespace between the name of an object-like macro and its replacement list (the tokens with which it is replaced).