linux初级入门-经典函数记录

offsetof

offsetof (type,member)

Return member offset
This macro with functional form returns the offset value in bytes of member member in the data structure or union type
type.

The value returned is an unsigned integral value of type
size_t with the number of bytes between the specified member and the beginning of its structure.

Parameters

typeA type in which member is a valid member designator.

C
C++98
C++11


type shall be a structure or union type.

type shall be a POD class (including unions).

type shall be a standard-layout class (including unions).

memberA member of type.

Return value

A value of type size_t with the offset value of
member in type.

Example

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

/* offsetof example */ #include <stdio.h> /* printf */ #include <stddef.h> /* offsetof */ struct foo { char a; char b[10]; char c; }; int main () { printf ("offsetof(struct foo,a) is %d\n",(int)offsetof(struct foo,a)); printf ("offsetof(struct foo,b) is %d\n",(int)offsetof(struct foo,b)); printf ("offsetof(struct foo,c) is %d\n",(int)offsetof(struct foo,c)); return 0; }

Output:

offsetof(struct foo,a) is 0 offsetof(struct foo,b) is 1 offsetof(struct foo,c) is 11

转自http://www.cplusplus.com/reference/cstddef/offsetof/