Here is another expression template which seems to be even more efficient based on some tests that I’ve run. In particular, it avoids creating multiple functions for strings with different lengths by specializing operator<< to use a char * member in the resulting structure. It should also be easy to add other specializations of this … Read more
Quote Wikipedia: Variable-argument macros were introduced in 1999 in the ISO/IEC 9899:1999 (C99) revision of the C language standard, and in 2011 in ISO/IEC 14882:2011 (C++11) revision of the C++ language standard. So it’s standard from C99 and C++11 onwards, but a GNU extension in C++03.
As for the updated question, by the use of auxiliary macro VA_ARGS like the following, the arguments will be expanded as expected. #define VA_ARGS(…) , ##__VA_ARGS__ #define CALL(f,…) FN(f)->call((ref(new LinkedList()) VA_ARGS(__VA_ARGS__)))
(Edit: See the end for a ready-made solution.) To get an overloaded macro, first we need a macro which selects between several implementations. This part doesn’t use a variadic macro. Then a variadic macro which generically counts its arguments produces a selector. Plugging the argument count into a dispatcher produces an overloaded macro. Caveat: This … Read more
It’s a variadic macro. It means you can call it with any number of arguments. The three … is similar to the same construct used in a variadic function in C That means you can use the macro like this DEBUG(“foo”, “bar”, “baz”); Or with any number of arguments. The __VA_ARGS__ refers back again to … Read more
Edit: This issue might be resolved by using /Zc:preprocessor or /experimental:preprocessor option in recent MSVC. For the details, please see here. MSVC’s preprocessor seems to behave quite differently from the standard specification. Probably the following workaround will help: #define EXPAND( x ) x #define F(x, …) X = x and VA_ARGS = __VA_ARGS__ #define G(…) … Read more
I usually use this macro to find a number of params: #define NUMARGS(…) (sizeof((int[]){__VA_ARGS__})/sizeof(int)) Full example: #include <stdio.h> #include <string.h> #include <stdarg.h> #define NUMARGS(…) (sizeof((int[]){__VA_ARGS__})/sizeof(int)) #define SUM(…) (sum(NUMARGS(__VA_ARGS__), __VA_ARGS__)) void sum(int numargs, …); int main(int argc, char *argv[]) { SUM(1); SUM(1, 2); SUM(1, 2, 3); SUM(1, 2, 3, 4); return 1; } void sum(int numargs, … Read more
There is an argument counting trick that you can use. Here is one standard-compliant way to implement the second BAR() example in jwd’s question: #include <stdio.h> #define BAR(…) printf(FIRST(__VA_ARGS__) “\n” REST(__VA_ARGS__)) /* expands to the first argument */ #define FIRST(…) FIRST_HELPER(__VA_ARGS__, throwaway) #define FIRST_HELPER(first, …) first /* * if there’s only one argument, expands to … Read more