Re: tlug: GCC compiler question

[Darren Cook <darren@example.com>]

>#define spin_lock_init(x)       do { (x)->lock = 0; } while(0)
>
>If it were used in the following way:
>
>if (true)
>     spin_lock_init (x);
>
>The semi-colon following "spin_lock_init (x);" will be consumed as
>part of the macro expansion as:
>
>if (true)
>   do { (x)->lock = 0; } while(0);
>
>
>If we were to declare the macro as follows:
>
>#define spin_lock_init(x)       { (x)->lock = 0; }
>
>Then this would expand to  
>
>if (true)
>   { (x)->lock = 0; }

Wouldn't it expand to this?

  if (true)
     { (x)->lock = 0; };

>...and not be syntactically correct, this will cause a compile error as
>no semi-colon is present.

Where is the syntax error?

>#define m(A) if(A){exp1; exp2;}
>
>You can see the problems with the semi-colon when this is expanded,
>we need to wrap it in a "do{ ... } while(0)".

Doesn't "m(myptr);" expand to this?

   if(myptr){exp1; exp2;};


Am I missing something obvious here?

Darren

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