Variadic macros
Variadic macros are function-like macros that contain a variable number of arguments.
Remarks
To use variadic macros, the ellipsis may be specified as the final formal argument in a macro definition, and the replacement identifier __VA_ARGS__ may be used in the definition to insert the extra arguments. __VA_ARGS__ is replaced by all of the arguments that match the ellipsis, including commas between them.
The C Standard specifies that at least one argument must be passed to the ellipsis to ensure the macro doesn't resolve to an expression with a trailing comma. The traditional Microsoft C++ implementation suppresses a trailing comma if no arguments are passed to the ellipsis. When the /Zc:preprocessor compiler option is set, the trailing comma isn't suppressed.
Example
// variadic_macros.cpp
#include <stdio.h>
#define EMPTY
#define CHECK1(x, ...) if (!(x)) { printf(__VA_ARGS__); }
#define CHECK2(x, ...) if ((x)) { printf(__VA_ARGS__); }
#define CHECK3(...) { printf(__VA_ARGS__); }
#define MACRO(s, ...) printf(s, __VA_ARGS__)
int main() {
CHECK1(0, "here %s %s %s", "are", "some", "varargs1(1)\n");
CHECK1(1, "here %s %s %s", "are", "some", "varargs1(2)\n"); // won't print
CHECK2(0, "here %s %s %s", "are", "some", "varargs2(3)\n"); // won't print
CHECK2(1, "here %s %s %s", "are", "some", "varargs2(4)\n");
// always invokes printf in the macro
CHECK3("here %s %s %s", "are", "some", "varargs3(5)\n");
MACRO("hello, world\n");
MACRO("error\n", EMPTY); // would cause error C2059, except VC++
// suppresses the trailing comma
}
here are some varargs1(1)
here are some varargs2(4)
here are some varargs3(5)
hello, world
error