使用arc后的url编码方法
NSString* escaped_value = (__bridge NSString *)CFURLCreateStringByAddingPercentEscapes( NULL, /* allocator */ (__bridge CFStringRef)value, NULL, /* charactersToLeaveUnescaped */ (CFStringRef)@"!*'();:@&=+$,/?%#[]", kCFStringEncodingUTF8); 需要加入__bridge