c - Purpose of #define foo() do { } while (0) -

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While browsing the sources of LinCAN driver, I found some macros that were bothering me. 

  # other / * CONFIG_PREEMPT * / #define can_preempt_disable () while doing (0) #define can_preempt_enable () while {0} #endif / * CONFIG_PREEMPT * /

I understand

utility of {...} ... if break (position); ...} while (0); Type a throw by using

break . I wrap the sequence of works like quote eg 

  #define FOO () do {foo (); times (); } While avoiding unconscious  if  I understand that sometimes "no-op statements" are required for #define, but this is particularly important to (0)

Why? In particular, empty braces, false conditions, while ... do? Some syntax warnings do not quite understand me?

This is: 

  #if! Defined (CONFIG_PREEMPT_RT) & amp; Amp; (Defined (CONFIG_PREEMPT) || (LINUX_VERSION_CODE & gt; = KERNEL_VERSION (2,6,0)) #define can_preempt_disable preempt_disable #define can_preempt_enable preempt_enable #else/ * CONFIG_PREEMPT * / #define can_preempt_disable () Make {} while (0) # In this way, the first part is the code that you get when you ask for pre-quarling protection, otherwise you get empty, not-nothing, loop.  
 I think they are common causes , I.e. to ensure that the macro is still a valid statement.  
> Definition A A termination should not be semicolon, because this will be the code using it, as it starts:  
  int c_can_wakeup_tx (struct canchip_t * chip, struct msgobj_t * obj) {Can_preempt_disable (); ..  
 
 Therefore, the macro is used like any other function call, and semicolon is correct where the macro is applied. This is very common. 
 
  UPDATE 2 : define this as ;  leads to double semicolon which is weak, at least in my opinion a  empty brace pair  {}  works  I think, but it < Creating code / time  is also more idiotic because it is often used in these cases. 
 
 <3> Update : As mentioned in a comment, a blank brace pair will not work since you can not insert a semicolon after the call. Ahh. Thanks!

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