dolfin team mailing list archive

["Martin Sandve Alnæs" <martinal@xxxxxxxxx>]

2008/3/25, Martin Sandve Alnæs <martinal@xxxxxxxxx>:
> 2008/3/25, Johan Hake <hake@xxxxxxxxx>:
>
> > On Tuesday 25 March 2008 13:38:22 Martin Sandve Alnæs wrote:
>
> >  > But what's the point of the "do { ... } while(false);" ??
>  >  > { ... } or just ... should be the same thing as far as I can see.
>  >
>  >
>  > It's because macros are evil! :)
>  >
>  >  http://www.parashift.com/c++-faq-lite/misc-technical-issues.html#faq-39.4
>  >
>  >  It looks like macros with if statements have a risk of nesting with the wrong
>  >  if, if it is used inside an other if statement. (Nice sentence! :) )
>
>
> Yes, but a simple {} should do the trick to define a local scope. No
>  need for do-while.


I stand corrected... Turns out this was the "naive solution", here's
the explanation:


The naive solution is to wrap the statements inside {...}, such as this:

 #define MYMACRO(a,b) \                (Bad)
     { \
         statement1; \
         statement2; \
         ... \
         statementN; \
     }

But this will cause compile-time errors with things like the following:

 if (whatever)
     MYMACRO(foo, bar);
 else
     baz;

since the compiler will see a } ; else which is illegal:

 if (whatever)
 {
     statement1;
     statement2;
     ...
     statementN;
 };  // ERROR: can't have }; before else
 else
     baz;


-- 
Martin