Re: Review: "int" and "gcd"

From: Gennadiy E. Rozental (rogeeff_at_[hidden])
Date: 2001-09-24 09:37:56

--- In boost_at_y..., Darin Adler <darin_at_b...> wrote:
> on 9/21/01 2:24 PM, Fernando Cacciola at fcacciola_at_g... wrote:
> 
> 
> > * What's the idea of  the 'do { ... } while ( false ) ; ' 
construct?
> 
> That's a standard C macro idiom for turning a set of statements 
into a
> single statement. It prevents problems with hanging ifs. Here's a 
simplified
> example.
> 
>     #define CALL_IF_0(num, func) if (!num) func()
> 
>     if (b)
>         CALL_IF_0(n, f);
>     else
>         g();
> 
> In the code above, the else gets attached to the if statement 
inside the
> macro. The do while false idiom fixes this:
> 
>     #define CALL_IF_0(num, func) do { if (!num) func() } while 
(false)
> 
>     if (b)
>         CALL_IF_0(n, f);
>     else
>         g();
> 
> The else gets attached to the proper if.
> 

It also could be used to simulate goto behaviour.

Gennadiy.

>     -- Darin