从NSString中提取URL

 1 NSString *src = @"<a href="http://weibo.com" rel="nofollow">新浪微博</a>"
 2 NSRange r=[src rangeOfString:@"<a href"];
 3         if (r.location!=NSNotFound) {
 4             
 5             NSRange start=[src rangeOfString:@"<a href=\""];
 6             if (start.location!=NSNotFound) {
 7                 int l=[src length];
 8                 NSRange fRange=NSMakeRange(start.location+start.length, l-start.length-start.location);
 9                 NSRange eRange=[src rangeOfString:@"\"" options:NSCaseInsensitiveSearch range:fRange];
10                 if (eRange.location!=NSNotFound) {
11                     
12                     r.location=start.location+start.length;
13                     r.length=eRange.location-r.location;
14                     NSString * sourceUrl=[src substringWithRange:r];
15                     
16                 }
17                 
18             }