The C++ compiler accepts #define preprocessor directives of the following form.
#define identifier (...) replacement_list #define identifier (identifier_list, ...) replacement_list |
If the macro parameter list ends with an ellipsis, an invocation of the macro is allowed to have more arguments than there are macro parameters. The additional arguments are collected into a single string, including commas, that can be referenced by the name __VA_ARGS__ in the macro replacement list. The following example demonstrates how to use a variable-argument-list macro.
#define debug(...) fprintf(stderr, __VA_ARGS__) #define showlist(...) puts(#__VA_ARGS__) #define report(test, ...) ((test)?puts(#test):\ printf(__VA_ARGS__)) debug(“Flag”); debug(“X = %d\n”,x); showlist(The first, second, and third items.); report(x>y, “x is %d but y is %d”, x, y); |
which results in the following:
fprintf(stderr, “Flag”); fprintf(stderr, “X = %d\n”, x); puts(“The first, second, and third items.”); ((x>y)?puts(“x>y”):printf(“x is %d but y is %d”, x, y)); |