格式化新浪微博日期成NSDate

- (NSDate *)dateFromString:(NSString *)string {

    //Wed Mar 14 16:40:08 +0800 2012

    if (!string) return nil;

   struct tm tm;

    time_t t;

    string=[string substringFromIndex:4];

    strptime([string cStringUsingEncoding:NSUTF8StringEncoding], "%b %d %H:%M:%S %z %Y", &tm);

    tm.tm_isdst = -1;

    t = mktime(&tm);

    return [NSDate dateWithTimeIntervalSince1970:t];

}