This is the yahoo news rss feed
<p><a href="http://us.rd.yahoo.com/dailynews/rss/us/*http://news.yahoo.com/s/ap/20110521/ap_on_re_us/us_michelle_obama_west_point"><img src="http://d.yimg.com/a/p/ap/20110520/capt.53a8af4c675f421c8b7cba014c589d29-53a8af4c675f421c8b7cba014c589d29-0.jpg?x=130&y=97&q=85&sig=iOyBvkyg0rEKSK3hjlSsNA--" align="left" height="97" width="130" alt="First lady Michelle Obama, left, and Lt. Gen. David Huntoon, superintendent at the U.S. Military Academy, arrive in Washington Hall for a graduation banquet, Friday, May 20, 2011, in West Point, N.Y. (AP Photo/Mike Groll)" border="0" /></a>AP - First lady Michelle Obama urged more than 1,000 cadets Friday night on the brink of graduating to keep in mind the families of the soldiers they will lead.</p><br clear="all"/>
我如何从此字符串中提取图像源（http://d.yimg.com/a/p/ap/20110520/capt.53a8af4c675f421c8b7cba014c589d29-53a8af4c675f421c8b7cba014c589d29-0.jpg）。
您可以使用NS扫描仪 http://developer.apple.com/library/ios/#documentation/Cocoa/Reference/Foundation/Classes/NSScanner_Class/Reference/Reference.html#//apple_ref/doc/uid/TP40003726。像这样的东西：
NSString *src = nil;
NSString *newsRSSFeed = @"<p><a href=\"http://us.rd.yahoo.com/dailynews/rss/us/*http://news.yahoo.com/s/ap/20110521/ap_on_re_us/us_michelle_obama_west_point\"><img src=\"http://d.yimg.com/a/p/ap/20110520/capt.53a8af4c675f421c8b7cba014c589d29-53a8af4c675f421c8b7cba014c589d29-0.jpg?x=130&y=97&q=85&sig=iOyBvkyg0rEKSK3hjlSsNA--\" align=\"left\" height=\"97\" width=\"130\" alt=\"First lady Michelle Obama, left, and Lt. Gen. David Huntoon, superintendent at the U.S. Military Academy, arrive in Washington Hall for a graduation banquet, Friday, May 20, 2011, in West Point, N.Y. (AP Photo/Mike Groll)\" border=\"0\" /></a>AP - First lady Michelle Obama urged more than 1,000 cadets Friday night on the brink of graduating to keep in mind the families of the soldiers they will lead.</p><br clear=\"all\"/>";
NSScanner *theScanner = [NSScanner scannerWithString:newsRSSFeed];
// find start of IMG tag
[theScanner scanUpToString:@"<img" intoString:nil];
if (![theScanner isAtEnd]) {
[theScanner scanUpToString:@"src" intoString:nil];
NSCharacterSet *charset = [NSCharacterSet characterSetWithCharactersInString:@"\"'"];
[theScanner scanUpToCharactersFromSet:charset intoString:nil];
[theScanner scanCharactersFromSet:charset intoString:nil];
[theScanner scanUpToCharactersFromSet:charset intoString:&src];
// src now contains the URL of the img
}
NSLog(@"%@",src);
// --> http://d.yimg.com/a/p/ap/20110520/capt.53a8af4c675f421c8b7cba014c589d29-53a8af4c675f421c8b7cba014c589d29-0.jpg?x=130&y=97&q=85&sig=iOyBvkyg0rEKSK3hjlSsNA--
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