前置声明：(forward declaration), 跟普通的声明一样，就是个声明, 没有定义。之所以叫前置声明，看下面一小段代码：
class Useful; // 对Userful类的前置声明
class Boss
{
Useful *userful_; // 实际要用到它的地方
};
<cstdarg>就能够使用c语言中<stdarg.h>里面定义的几个宏来完成变长参数的处理，先看一个实例：
...
| 类型 | 锚点 | 忽略锚点 | contentSize | position | 直接父类 | 备注 |
|---|---|---|---|---|---|---|
| CCNode | (0,0) | false | (0, 0) | (0, 0) | CCObject | |
| CCNodeRGBA | 同CCNode | 同CCNode | 同CCNode | 同CCNode | CCNode | |
| CCDrawNode | 同CCNode | 同CCNode | 同CCNode | 同CCNode | CCNode | |
| CCAtlasNode | 同CCNode | 同CCNode | 同CCNode | 同CCNode | CCNode |
Good programming is notoriously difficult to teach. Programming books generally all start out in the same way: “Here is an example of an X, and here is an example.”. Teaching the building blocks is easy. There are only so many. The hard part is teaching the consequences of each choice. The common advice is to write a lot of code to get good. This is necessary but not sufficient. To learn we still need to decide what code to write, and how to improve that code. ...