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How do you read the second line of this macro? What does (type *)0 mean in this context?
#define container_of(ptr, type, member) ({ \
const typeof( ((type *)0)->member ) *__mptr = (ptr); \
(type *)( (char *)__mptr - offsetof(type,member) );})
You’re finding the type of
((type *)0)->member. It’s not actually dereferencing the pointer (that would be madness, I tell you. Madness!)It’s a weirdness of C. Maybe it would make more sense if they wrote
typeof(type.member)but sadly that is not allowed.