list.h linux用户控件,(转)linux之list.h用户使用态

((size_t) &(type

*)0)->member)把0地址转化为type结构的指针，然后获取该结构中member成员的指针，并将其强制转换为size_t类型。于是，由于结构从0地址开始定义，因此，这样求出member的成员地址，实际上就是它在结构中的偏移量。为了更好的理解这些，我们可以写一段程序来验证:

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#include

#include

struct foobar{

unsigned int foo;

char bar;

char boo;

};

int main(int argc, char** argv){

struct foobar tmp;

printf("address of &tmp is= %p\n\n", &tmp);

printf("address of tmp->foo= %p \t offset of tmp->foo= %lu\n", &tmp.foo, (unsigned long) &((struct foobar *)0)->foo);

printf("address of tmp->bar= %p \t offset of tmp->bar= %lu\n", &tmp.bar, (unsigned long) &((struct foobar *)0)->bar);

printf("address of tmp->boo= %p \t offset of tmp->boo= %lu\n\n", &tmp.boo, (unsigned long) &((struct foobar *)0)->boo);

printf("computed address of &tmp using:\n");

printf("\taddress and offset of tmp->foo= %p\n",

(struct foobar *) (((char *) &tmp.foo) - ((unsigned long) &((struct foobar *)0)->foo)));

printf("\taddress and offset of tmp->bar= %p\n",

(struct foobar *) (((char *) &tmp.bar) - ((unsigned long) &((struct foobar *)0)->bar)));

printf("\taddress and offset of tmp->boo= %p\n",

(struct foobar *) (((char *) &tmp.boo) - ((unsigned long) &((struct foobar *)0)->boo)));

return 0;

}

Output from this code is:

address of &tmp is= 0xbfffed00

address of tmp->foo= 0xbfffed00 offset of tmp->foo= 0

address of tmp->bar= 0xbfffed04 offset of tmp->bar= 4

address of tmp->boo= 0xbfffed05 offset of tmp->boo= 5

computed address of &tmp using:

address and offset of tmp->foo= 0xbfffed00

address and offset of tmp->bar= 0xbfffed00

address and offset of tmp->boo= 0xbfffed00

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到此，我们对链表的实现机制有所了解，但在此止步的话，我们依然无法领略这风景背后的韵味。

尽管list.h是内核代码中的头文件，但我们可以把它移植到用户空间使用。且看下一讲，链表接口之应用。