Variadic Macros

The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.

The latest version of this topic can be found at 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 that the macro does not resolve to an expression with a trailing comma. The Visual C++ implementation will suppress a trailing comma if no arguments are passed to the ellipsis.

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  
}  

Output

here are some varargs1
(1)  
here are some varargs2
(4)  
here are some varargs3
(5)  
hello, world  
error  

See Also

Macros (C/C++)