search.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#include <u.h>
#include <libc.h>
#include <bio.h>
#include <thread.h>
#include "object.h"
#include "parse.h"
#include "search.h"

Object *
search(Object *rt, Object *parent, Reprog *preg) {
	/* Create a `search object', a subtree of rt containing
	 * only objects with s in their value of key fields plus
	 * their parentage.
	 *
	 * Algorithm: depth-first traversal of rt.  On the way down,
	 * copy rt to nr (new root), on the way back up, delete
	 * subtrees without match.
	 *
	 * returns null when there are no matches in rt's subtree
	 */
	Object *o, *nr;
	char *s;
	int i;
	int yes = 0;

	nr = newobject(rt->type, parent);
	nr->orig = rt->orig?rt->orig:rt;
	nr->value = rt->value;
	strncpy(nr->key, rt->key, KEYLEN);

	if((((s = nr->value)) && regexec(preg, s, nil, 0) == 1)
	|| (((s = nr->value)) && regexec(preg, s, nil, 0) == 1))
		yes = 1;
	for(i = 0; i < rt->nchildren; i++)
		if((o = search((Object*)rt->children[i], nr, preg))){
			yes = 1;
			addchild(nr, o, "search");
		}
	if(yes == 0){
		freeobject(nr, "s");
		return nil;
	}
	return nr;
}