From: Stefan Strasser (sstrasser_at_[hidden])
Date: 2005-05-10 17:39:37
Dave Steffen schrieb:
> Another question about the to-be-released FOREACH macro, which I find
> I am using heavily... (BTW - Thanks Eric for your quick responses, and
> for the cool macro!)
>
> The issue is declaring the 'loop variable' for maps. For example,
>
>
> vector<int> v;
> ...
> FOREACH (int a, v) { ... } // this compiles
> int b;
> FOREACH (b, v) {...} // this also compiles
>
> However, for maps, the second variation (declaring outside the macro)
> doesn't work:
>
> map<int,int> m;
> ...
> FOREACH (map<int,int>::value_type i, m) {...} // compiles
> map<int,int>::value_type i;
> FOREACH (i, m) {...} // COMPILE ERROR
>
>
> Specifically, the compiler says
>
> error: non-static const member
> ` const int std::pair<const int,int>::first',
> can't use default assignment operator
>
> (from GCC 3.3.1). Despite my best efforts, I can't figure out what
> this error means, or what it's talking about. Anybody else run into
> this? Any thoughts?
>
this also doesn't work:
map<int,int>::value_type i;
i=std::pair<int,int>(1,2); // error
that's because map<Key,Value>::value_type is defined to
std::pair<Key /**/const/**/,Value>.
and that's probably because you're not allowed to change the key of a
map entry when you're e.g. iterating over the map.
just use std::pair<int,int> instead and your example compiles.
-- Stefan Strasser