🚀 go-pugleaf

rmartin@rcmcon.com (Robert Martin) writes:
>In reading the WP I see that the scope of variables declared in 'for'
>statements is now identical with the scope of variables declared in
>'if' and 'while' statements...

>Do I have this right?  If so, doesn't this break a lot of old C++
>programs that depended upon variables declared in the 'for' statement
>being local to the enclosing scope.

Yes, this change breaks a great deal of old code.  As best I can
determine, when gcc-2.7.0 implemented this change every significant-sized
C++ program I'm aware of (including all of the more popular freely
redistributable C++ programs) had at least some breakage; hundreds of
distinct cases are often found.  That's why it's so important to provide
backward compatibility flags (-fno-for-scope, in the case of gcc).

It is possible to use the old scope rule (together with warnings) in
the very common case where there would otherwise be a reference to
an undefined variable when the new rule is used.  gcc-2.7.1 will
do this.  Thus in Robert's example

>for (int i=0; i<100; i++)
>{
>  // expressions using i;
>}
>
>if (i == 100) // loop ran to end.

provided that there is no i in a more global scope, the compiler will
issue a warning and then proceed using the old rule.  This permits most
old programs to build.  This can't be done if i is an object with a
destructor rather than an int.



-- 
-- Joe Buck 	<jbuck@synopsys.com>	(not speaking for Synopsys, Inc)
Anagrams for "information superhighway":	Enormous hairy pig with fan
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