Re: [Boost-users] FOREACH with maps

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 m; ... FOREACH (map::value_type i, m) {...} // compiles map::value_type i; FOREACH (i, m) {...} // COMPILE ERROR

Specifically, the compiler says

error: non-static const member ` const int std::pair::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::value_type i; i=std::pair(1,2); // error that's because map::value_type is defined to std::pair. 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 instead and your example compiles. -- Stefan Strasser