Linux C编程小例子——pwd命令的实现

#include
#include
#include
#include
#include
ino_t get_inode(char *);
void printpathto(ino_t);
void inum_to_name(ino_t, char *, int);

int main() {
printpathto(get_inode(".")); /* print path to here */
putchar('\n'); /* then add newline */
return 0;
}

/*
* prints path leading down to an object with this inode
* kind of recursive
*/
void printpathto(ino_t this_inode) {
ino_t my_inode;
char its_name[BUFSIZ];
if (get_inode("..") != this_inode) {
chdir(".."); /* up one dir */
inum_to_name(this_inode, its_name, BUFSIZ);/* get its name*/
my_inode = get_inode("."); /* print head */
printpathto(my_inode); /* recursively */
printf("/%s", its_name); /* now print name of this */
}
}
void inum_to_name(ino_t inode_to_find, char *namebuf, int buflen) {
DIR *dir_ptr; /* the directory */
struct dirent *direntp; /* each entry */
dir_ptr = opendir(".");
if (dir_ptr == NULL) {
perror(".");
exit(1);
}/* search directory for a file with specified inum */
while ((direntp = readdir(dir_ptr)) != NULL)
if (direntp->d_ino == inode_to_find) {
strncpy(namebuf, direntp->d_name, buflen);
namebuf[buflen - 1] = '\0'; /* just in case */
closedir(dir_ptr);
return;
}
fprintf(stderr, "error looking for inum %d\n", inode_to_find);
exit(1);

}

/*
* returns inode number of the file
*/
ino_t get_inode(char *fname) {
struct stat info;

if (stat(fname, &info) == -1) {
fprintf(stderr, "Cannot stat ");
perror(fname);
return 1;
}
return info.st_ino;
}