What's The Deal With __attribute and __attribute__?

I heard you could utilize in the g++ compiler the __attribute and __attribute__ keywords. What's the difference between these two? If __attribute__((noreturn)) can be used on a void function or a function that never returns to optimize the compiler/clear up code, then why isn't everyone using it?!?

const int init()__attribute__((const))
void foo()__attribute__((noreturn))

Did you read the GCC manual before asking question 1?

> then why isn't everyone using it?!?
Well
a) very few functions can be classed as noreturn to begin with
b) all attributes are GCC specific, so have no place in portable code
c) people are lazy bums