17.All the information in the i-node is stored separately from the actual contents of the file.
18.A directory is simply a file containing directory entries:filenames and associated i-node numbers.
19.
typedef的一个用法:
typedef int Func(int a,int b); //这声明了一个新的函数类型，Func,这种函数类型有两个int类型的参数，返回值也是int类型
static Func my_func1; //my_func1的函数原型,完整的写法是static int my_func1(int a ,int b);
在这里使用typedef，会使得代码更加简洁，清晰，对代码的可读性有好处
20.
char *p; *p++='0'; 是将*p赋值为'0'后，p指针再加1个单位的地址
*++p='0'; 是先将p执行加一个单位的地址后，再将*p赋值为'0';
这是一个比较容易混淆和容易记错的地方
21.char *ptr; ptr[-1]是指是的ptr指向位置的上一个元素。
22.The current working directory is an attribute of a process .
23. If we try,using either open or creat,to create a file that alredy exists,the file's access permission bits are not changed but the files were truncated(被清空).
24.The size of a directory should never be 0,since there should always be entries for dot and dot-dot.The size of a symbolic link is the number of characters in the pathname contained in the symbolic link,and this pathname must always contain at least one character.
25.time ./pro1 计算整个pro1程序执行的时间
26.The kernel has no inherent limit on the depth of a directory tree.But many commands will fail on pathnames that exceed PATH_MAX,比如getcwd.
参考资料:apue