Linux C编程小例子——pwd命令的实现

#include	<stdio.h>
#include	<sys/types.h>
#include	<sys/stat.h>
#include	<dirent.h>
#include     <pwd.h>
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;
}