Re: for in D versus C and C++

[Denis Koroskin]

On Thu, 19 Mar 2009 20:32:54 +0300, Walter Bright <newshou...@digitalmars.com> 
wrote:

BCS wrote:

Thu, 19 Mar 2009 06:35:37 -0400, Steve Teale wrote:

for (; a<b; a++);

is illegal in D.

Doesn't this break a lot of C and C++ code?

for (; a<b; a++) {}

is legal.  I don't think that an empty statement after for is used in
"a lot of code."

 it's a trivial fix and easy to find. Heck, you hardly need to think!

No, it isn't easy to find. This is in D because a colleague of mine, who was an expert C programmer (the best in the company I was working for), came to me with:

for (xxx; i < 10; i++);
{
      ... code ...
}

and said he could not figure out why his loop executed only and exactly once. He'd fiddled with it for a whole afternoon. He said he must be missing something obvious. I said you've got an extra ; after the ). He smacked his head and about fell over backwards.

So it's illegal in D, along with:

    if (condition);

and similar constructs. Have to use a { } to indicate a blank statement.

Funny enough, or programming department chief posted the following question in 
our corporate newsgroup:

Why the hell this function enters infinite loop?

void treeWalkWithoutRecursion( Node* head )
{
   Stack   s;
   s.push( head );
   while ( !s.empty() );
   {
       Node* tmp = s.pop();
       if ( !tmp->marked )
       {
           if ( tmp->right  )
               s.push( tmp->right );
           s.push( tmp );
           if ( tmp->left )
               s.push( tmp->left );
           tmp->marked = true;
       }
       else
           doSomeThing( tmp );
   }
}