Understanding Unix/Linux Programming-pwd指令练习

             1 #include <sys/types.h>
 2 #include <sys/stat.h>
 3 #include <unistd.h>
 4 #include <stdio.h>
 5 #include <dirent.h>
 6 #include <stdlib.h> // Just in case of some calls 7 8 ino_t get_inode(char *) ; 
 9void printpathto(ino_t) ;
10void inum_to_name(ino_t , char * , int ) ;
1112int main()
13{
14     printpathto(get_inode("."));
15     putchar(‘\n‘);
16return0 ;
17}
1819void printpathto(ino_t this_inode)
20{
21    ino_t my_inode ;
22char its_name[BUFSIZ] ;
23if(get_inode("..") != this_inode)
24    {
25         chdir("..") ;
26        inum_to_name(this_inode , its_name , BUFSIZ) ;
27         my_inode = get_inode(".");
28        printpathto( my_inode ) ;
29         printf("/%s", its_name );
30    }
31}
3233void inum_to_name(ino_t inode_to_find , char namebuf[] , int buflen)
34{
35     DIR * dir_ptr ;
36struct dirent * direntp ;
37     dir_ptr = opendir(".") ;
38if(dir_ptr == NULL )
39    {
40         perror(".");
41         exit(1);
42    }
43while( (direntp = readdir(dir_ptr)) != NULL )
44    {
45if(direntp -> d_ino == inode_to_find )
46        {
47             strncpy(namebuf , direntp -> d_name , buflen );
48             namebuf[buflen - 1 ] = ‘\0‘ ; // The book says : just in case of a mistake49            closedir(dir_ptr) ;
50return ;
51        }
52    }
53     fprintf(stderr, "%s\n", "Error looking for inode_num:" , inode_to_find );
54     exit(1) ;
55}    
5657 ino_t get_inode(char * fname)
58{
59struct stat info ;
60if(stat(fname , &info ) != -1 )
61    {
62return info.st_ino ;
63    }
64else65    {
66         fprintf(stderr, "%s\n", "Can not stat." );
67        perror(fname) ;
68         exit(1) ;
69    }
70 }