unix/linux編程實踐教程：pwd命令

1. pwd命令通過不斷讀取上層目錄，來進行遞歸查找目錄名。當路徑"."的i結點等於路徑".."的i結點，說明已經到達了根目錄，顯示出來即可。

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

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

int main()
{
	printpathto( get_inode( "." ) );
	putchar( '\n' );
	return 0;
}

void printpathto( ino_t this_inode )
{
	ino_t my_inode;
	char	its_name[ BUFSIZ ];
	if ( get_inode( ".." ) != this_inode ){
		chdir( ".." );
		inum_to_name( this_inode, its_name, BUFSIZ );
		my_inode = get_inode( "." );
		printpathto( my_inode );
		printf("/%s", its_name );
	}
}

void inum_to_name( ino_t inode_to_find, char *namebuf, int buflen )
{
	DIR	*dir_ptr;
	struct dirent *direntp;
	dir_ptr = opendir( "." );
	if ( dir_ptr == NULL ){
		perror(".");
		exit( 1 );
	}
	while ( ( direntp = readdir( dir_ptr ) ) != NULL )
		if ( direntp->d_ino == inode_to_find ){
			strncpy( namebuf, direntp->d_name, buflen );
			closedir( dir_ptr );
			return;
		}
	fprintf( stderr, "error looking for inum %d\n", inode_to_find );
	exit( 1 );
}

ino_t get_inode( char *fname )
{
	struct stat info;
	if ( stat( fname, &info ) == -1 ){
		fprintf(stderr, "cannot stat" );
		perror( fname );
		exit( 1 );
	}
	return info.st_ino;
}