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

/* Maybe use perror() for readdir() setting errno? */

void tab(int num_spaces) 
{
	for ( ; num_spaces>0; num_spaces--)
		putchar(' ');
} 

void walk_tree (char *path, int level)
{
	DIR *pdir;
	struct dirent *entry;

	pdir = opendir(path);
	if (!pdir) {
		/* could check errno */
                /* to see why        */
		fprintf(stderr, "Unable to open directory: %s\n", path); 
		return; 
	}
	fprintf(stderr, "Opened directory: %s\n", path);
  
	while (errno = 0, entry = readdir(pdir)) {
		tab(level);
		printf("  %s\n", entry->d_name);
		/* If entry is a directory, traverse it. */
	}

	if (errno != 0) fprintf(stderr, "Unable to readdir: %s", path);

	if (closedir(pdir) == -1)
		fprintf(stderr, "Error closing directory: %s\n", path);
  
	return;
} /* walk_tree() */

int main(int argc, char* argv[])
{
	char *path;

	/* We are either
	   - called with exactly one argument, which is the
	   pathname of a directory in which to start our traversal, or
	   - called with no arguments, in which case we start with
	   the current working directory.
	*/
	if (argc > 2) {
		fprintf(stderr, "Usage: %s [pathname]\n", argv[0]);
		exit(-1);
	}
	if (argc == 2)
		path = argv[1];
	else
		path = ".";

	walk_tree(path, 0);
} /* main() */