ACE网络编程之ACE_NEW_RETURN，ACE_NEW，ACE_NEW_NORETURN

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ACE源码OS_Memory.h是这样定义的。

#  if defined (ACE_HAS_NEW_NOTHROW)#    define ACE_NEW_RETURN(POINTER,CONSTRUCTOR,RET_VAL) \   do { POINTER = new (ACE_nothrow) CONSTRUCTOR; \     if (POINTER == 0) { errno = ENOMEM; return RET_VAL; } \   } while (0)#    define ACE_NEW(POINTER,CONSTRUCTOR) \   do { POINTER = new(ACE_nothrow) CONSTRUCTOR; \     if (POINTER == 0) { errno = ENOMEM; return; } \   } while (0)#    define ACE_NEW_NORETURN(POINTER,CONSTRUCTOR) \   do { POINTER = new(ACE_nothrow) CONSTRUCTOR; \     if (POINTER == 0) { errno = ENOMEM; } \   } while (0)#  else#    define ACE_NEW_RETURN(POINTER,CONSTRUCTOR,RET_VAL) \   do { try { POINTER = new CONSTRUCTOR; } \     catch (ACE_bad_alloc) { ACE_del_bad_alloc errno = ENOMEM; POINTER = 0; return RET_VAL; } \   } while (0)#    define ACE_NEW(POINTER,CONSTRUCTOR) \   do { try { POINTER = new CONSTRUCTOR; } \     catch (ACE_bad_alloc) { ACE_del_bad_alloc errno = ENOMEM; POINTER = 0; return; } \   } while (0)#    define ACE_NEW_NORETURN(POINTER,CONSTRUCTOR) \   do { try { POINTER = new CONSTRUCTOR; } \     catch (ACE_bad_alloc) { ACE_del_bad_alloc errno = ENOMEM; POINTER = 0; } \   } while (0)#  endif /* ACE_HAS_NEW_NOTHROW */#else /* ACE_NEW_THROWS_EXCEPTIONS */# define ACE_NEW_RETURN(POINTER,CONSTRUCTOR,RET_VAL) \   do { POINTER = new CONSTRUCTOR; \     if (POINTER == 0) { errno = ENOMEM; return RET_VAL; } \   } while (0)# define ACE_NEW(POINTER,CONSTRUCTOR) \   do { POINTER = new CONSTRUCTOR; \     if (POINTER == 0) { errno = ENOMEM; return; } \   } while (0)# define ACE_NEW_NORETURN(POINTER,CONSTRUCTOR) \   do { POINTER = new CONSTRUCTOR; \     if (POINTER == 0) { errno = ENOMEM; } \   } while (0)

以上是用宏定义替换的表达式，功能都是用一个POINTER指针new一个CONSTRUCTOR实例，内部做了一些错误信息的标志和异常处理。
宏ifelse对平台的不同进行了分离，每个平台下都有三种new的方法，他们的区别是return。

每个宏定义都用到了do{}while(0)，是因为宏只能替换一句表达式，而你用do{}while(0)可以方便的把多个表达式集中起来。

转自：http://www.cppblog.com/cxiaojia/archive/2013/03/26/198838.html