typeof operator

http://gcc.gnu.org/onlinedocs/gcc/Typeof.html

 

typeof is a way to refer to the type of an expression, supported by gcc

e.g.

#define max(a, b)/

({typeof(a) _a = (a);/

typeof(b) )_b =(b);/

_a>_b?_a:_b;})

To declare y as an array of the same type as x:

typeof (x) y[4];

又如： #define pointer(T) typeof(T*)

 

e.g. to cast a member of a structure to the container structure

#define container_of(ptr, type, member) ({ /

             const typeof(((type *)0)->member)) *__mptr = (ptr); /

            (type *)( (char *)__mptr - offsetof(type, member));  })

#define offsetof(TYPE, MEMBER)  ((size_t)&((TYPE *)0)->MEMBER)