c 语言 __P()宏

          The __P() macro is usually used to support C implementations from the days of K&R C, when there were no prototypes (which were introduced to C with C89)。

          代码如下：

#if defined(__STDC__) || defined(__cplusplus)
#define __P(protos)     protos          /* full-blown ANSI C */
#else   /* !(__STDC__ || __cplusplus) */
#define __P(protos)     ()              /* traditional C preprocessor */
#endif  /* !__GNUC__ */

          是用来和特别老的编译器进行兼容的，基本可以忽略。