[定义](%E5%AE%9A%E4%B9%89.md) [常用操作](%E5%B8%B8%E7%94%A8%E6%93%8D%E4%BD%9C.md) [预定义常量](%E9%A2%84%E5%AE%9A%E4%B9%89%E5%B8%B8%E9%87%8F.md) [魔术常量](%E9%AD%94%E6%9C%AF%E5%B8%B8%E9%87%8F.md)