Re: C help please - C newbie

"John R. Strohm" <[EMAIL PROTECTED]> wrote in
news:[EMAIL PROTECTED]: 

>> > Not if the compiler can determine that they're no longer needed after
>> > some point in program flow.  They must behave *as if* they persisted
>> > for the duration of the program --- but if the program doesn't look,
>> > the compiler is allowed to re-use the space otherwise.
>>
>> I'd like to know if you have an example of such a condition as I'm
>> having a hard time seeing how a compiler could know that it will swap
>> out a function for use by another. Maybe I'm too used to Harvard
>> architectures. 
> 
> Observe.
> 
> static int switch = 0;
> static int x;
> static int y;
> 
> void test(void){
>   if (switch == 0) {
>     do a whole bunch of stuff with x
>     if (some interesting case) {
>       switch = 1;
>     }
>     do a bunch of stuff with y;
>   } else {
>     do a bunch of other stuff with y;
>   }
> }
> 
> Observe that the switch initially points to x, and the program uses x. 
> Once the switch is thrown to y, the program only uses y, and NEVER AGAIN
> TOUCHES X.  A sufficiently-advanced compiler could, in principle, notice
> that x and y have disjoint lifetimes, and use the same storage location
> for the two variables.

First, you can't have a variable names 'switch' since this is a keyword.
Second, I was asking about static not not having program duration for a
function, not a variable. 

Thanks.

-- 
- Mark ->
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