| title |
Variadic Macros | Microsoft Docs |
| ms.custom |
|
| ms.date |
11/04/2016 |
| ms.reviewer |
|
| ms.suite |
|
| ms.technology |
|
| ms.tgt_pltfrm |
|
| ms.topic |
article |
| dev_langs |
|
| helpviewer_keywords |
variadic macros [C++] |
__VA_ARGS__ variadic macro specifier |
|
| ms.assetid |
51e757dc-0134-4bb2-bb74-64ea5ad75134 |
| caps.latest.revision |
12 |
| author |
corob-msft |
| ms.author |
corob |
| manager |
ghogen |
| translation.priority.ht |
de-de |
es-es |
fr-fr |
it-it |
ja-jp |
ko-kr |
ru-ru |
zh-cn |
zh-tw |
|
| translation.priority.mt |
|
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.
// 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
Macros (C/C++)