What does __VA_ARGS__ in a macro mean?

Question

/* Debugging */ #ifdef DEBUG_THRU_UART0 #   define DEBUG(...)  printString (__VA_ARGS__) #else void dummyFunc(void); #   define DEBUG(...)  dummyFunc()    #endif 

I've seen this notation in different headers of C programming, I basically understood it's passing arguments, but I didn't understand what this "three dots notation" is called?

Can someone explain it with example or provide links also about VA Args?

Answer 1

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 the variable arguments in the macro itself.

#define DEBUG(...)  printString (__VA_ARGS__)                ^                     ^                +-----<-refers to ----+ 

So DEBUG("foo", "bar", "baz"); would be replaced with printString ("foo", "bar", "baz")