#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER);
2011-09-26 16:27
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offsetof(TYPE, MEMBER)
该宏在Linux内核代码(版本2.6.22)中定义如下:
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER);
分析:
(TYPE *)0,将 0 强制转换为 TYPE 型指针,记 p = (TYPE *)0,p是指向TYPE的指针,它的值是0。那么 p->MEMBER 就是 MEMBER 这个元素了,而&(p->MEMBER)就是MENBER的地址,而基地址为0,这样就巧妙的转化为了TYPE中的偏移量。再把结果强制转换为size_t型的就OK了,size_t其实也就是int。
typedef __kernel_size_t size_t;
typedef unsigned int __kernel_size_t;
可见,该宏的作用就是求出MEMBER在TYPE中的偏移量。成员变量的入口地址
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