# if ! defined (ACE_RCSID)
// This hack has the following purposes:
// 1. To define the RCS id string variable as a static char*, so
// that there won't be any duplicate extern symbols at link
// time.
// 2. To have a RCS id string variable with a unique name for each
// file.
// 3. To avoid warnings of the type "variable declared and never
// used".
# define ACE_RCSID(path, file, id) /
static inline const char* get_rcsid_ ## path ## _ ## file (const char*) /
{ /
return id ; /
} /
static const char* rcsid_ ## path ## _ ## file = /
get_rcsid_ ## path ## _ ## file ( rcsid_ ## path ## _ ## file ) ;
# endif /* #if ! defined (ACE_RCSID) */
#else
// RCS id strings are not wanted.
# if defined (ACE_RCSID)
# undef ACE_RCSID
# endif /* #if defined (ACE_RCSID) */
# define ACE_RCSID(path, file, id) /* noop */
#endif /* #if (defined (ACE_USE_RCSID) && (ACE_USE_RCSID != 0)) */
根据程序和英文注释，他的用处是根据你输入的三个参数生成一个唯一的ID。他的作用有三点（翻译的不是很准确，原文是上面的蓝字）：1。避免外部引用冲突；2。为每个文件起一个独一无二的名字；3。避免编译器保“ariable declared and never used"的警告 。