Variadic Macros

3.6 Variadic Macros

A macro can be declared to accept a variable number of arguments much as a function can. The syntax for defining the macro is similar to that of a function. Here is an example:

#define eprintf(...) fprintf (stderr, __VA_ARGS__)

This kind of macro is called variadic. When the macro is invoked, all the tokens in its argument list after the last named argument (this macro has none), including any commas, become the variable argument. This sequence of tokens replaces the identifier __VA_ARGS__ in the macro body wherever it appears. Thus, we have this expansion:

eprintf ("%s:%d: ", input_file, lineno)
     ==>  fprintf (stderr, "%s:%d: ", input_file, lineno)

The variable argument is completely macro-expanded before it is inserted into the macro expansion, just like an ordinary argument. You may use the ‘#’ and ‘登录查看完整内容