Question

The documentation for GCC’s __attribute__((...)) syntax indicates that attributes must be surrounded by double parentheses, but does not give a rationale for this design decision.

What practical reason would have caused GCC’s designers to require this? Does it have anything to do with the preprocessor’s handling of double parentheses?

Answer 1

To make it easier to eliminate it for different compiler. If you have portable code, you have to remove them for other compilers, so you do

#ifndef __GNUC__
#define __attribute__(x)
#endif

The problem is that attributes have various number of arguments and you can combine multiple attributes in one __attribute__ declaration, but C only introduced variadic macros in C99. With double parenthesis the above definition does not need variadic macros.