std::nothrow

1、在内存不足时，new (std::nothrow)并不抛出异常，而是将指针置NULL。

若不使用std::nothrow,则分配失败时程序直接抛出异常。

2、使用方式：

1 #include 
      
          2 #include 
       
         // for std::cerr   3 #include 
        
          // for std::exit()   4 Task * ptask = new (std::nothrow) Task;   5 if (!ptask)   6 {   7 std::cerr<<"allocation failure!";   8 std::exit(1);   9 }  10 //... allocation succeeded; continue normally
        
       
      

1 #include 
      
         2 std::nothrow_t nt;  3 Task * ptask = new (nt) Task; //user-defined argument  4 if (!ptask)  5 //...
      

3、分配失败是非常普通的，它们通常在植入性和不支持异常的可移动的器件中发生更频繁。因此，应用程序开发者在这个环境中使用nothrow new来替代普通的new是非常安全的。

 4、一种宏实现的方式，取自ACE：

1 #   define ACE_nothrow   ::std::nothrow 2 #   define ENOMEM          12 3 #   define errno (* (ACE_CE_Errno::instance ())) 4  5 #if defined (ACE_NEW_THROWS_EXCEPTIONS) 6 #  if defined (ACE_HAS_NEW_NOTHROW) 7 #    define ACE_NEW_RETURN(POINTER,CONSTRUCTOR,RET_VAL) \ 8    do { POINTER = new (ACE_nothrow) CONSTRUCTOR; \ 9      if (POINTER == 0) { errno = ENOMEM; return RET_VAL; } \10    } while (0)11 #    define ACE_NEW(POINTER,CONSTRUCTOR) \12    do { POINTER = new(ACE_nothrow) CONSTRUCTOR; \13      if (POINTER == 0) { errno = ENOMEM; return; } \14    } while (0)15 #    define ACE_NEW_NORETURN(POINTER,CONSTRUCTOR) \16    do { POINTER = new(ACE_nothrow) CONSTRUCTOR; \17      if (POINTER == 0) { errno = ENOMEM; } \18    } while (0)19 20 #  else21 22 #    define ACE_NEW_RETURN(POINTER,CONSTRUCTOR,RET_VAL) \23    do { try { POINTER = new CONSTRUCTOR; } \24      catch (ACE_bad_alloc) { ACE_del_bad_alloc errno = ENOMEM; POINTER = 0; return RET_VAL; } \25    } while (0)26 27 #    define ACE_NEW(POINTER,CONSTRUCTOR) \28    do { try { POINTER = new CONSTRUCTOR; } \29      catch (ACE_bad_alloc) { ACE_del_bad_alloc errno = ENOMEM; POINTER = 0; return; } \30    } while (0)31 32 #    define ACE_NEW_NORETURN(POINTER,CONSTRUCTOR) \33    do { try { POINTER = new CONSTRUCTOR; } \34      catch (ACE_bad_alloc) { ACE_del_bad_alloc errno = ENOMEM; POINTER = 0; } \35    } while (0)36 #  endif /* ACE_HAS_NEW_NOTHROW */37 38 #else /* ACE_NEW_THROWS_EXCEPTIONS */39 40 # define ACE_NEW_RETURN(POINTER,CONSTRUCTOR,RET_VAL) \41    do { POINTER = new CONSTRUCTOR; \42      if (POINTER == 0) { errno = ENOMEM; return RET_VAL; } \43    } while (0)44 # define ACE_NEW(POINTER,CONSTRUCTOR) \45    do { POINTER = new CONSTRUCTOR; \46      if (POINTER == 0) { errno = ENOMEM; return; } \47    } while (0)48 # define ACE_NEW_NORETURN(POINTER,CONSTRUCTOR) \49    do { POINTER = new CONSTRUCTOR; \50      if (POINTER == 0) { errno = ENOMEM; } \51    } while (0)52 #endif

使用时：

1 ACE_Thread_Descriptor *thr_desc = 0;2 ACE_NEW_RETURN (thr_desc,3                       ACE_Thread_Descriptor,4                       -1);