Re: [Boost-users] BOOST_FOREACH and maps

Dave Steffen wrote:

Sebastian Redl writes:

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On Mon, September 18, 2006 12:52 pm, Rob Caldecott wrote:

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Can the pair be declared without a typedef? Is this a limitation of the MS compiler?

It is a limitation of the preprocessor. It does not recognize <> as any sort of parentheses, so it thinks the , separating the template parameters is a macro argument separator.

You can try wrapping the whole argument in parentheses: BOOST_FOREACH((std::pair p), m)

But I'm not sure if the PP passes the parentheses on - in that case, you might get syntax errors in the generated code. If that's the case, you'll have to use the typedef.

I've done something like this:

#include "boost/tuple/tuple.hpp"

#define FOREACH_PAIR( KEY, VAL, COL) FOREACH (boost::tie(KEY,VAL),COL)

// and then, for example

int key, value;

FOREACH_PAIR(key, value m);

It's not perfect; specfically, I don't think that you can write into the map this way. I suspect there _is_ a way for that to work, I just haven't figured it out yet. :-)

I'd like the eventual "official" FOREACH to have some additional variations like this...

Boost.Parameter(cvs head) seems to already have a workaround for it. #include #define UNPARENTHESIZE BOOST_PARAMETER_PARENTHESIZED_TYPE int main() { std::map m; BOOST_FOREACH ( UNPARENTHESIZE((std::pair)) p, m ) { } } -- Shunsuke Sogame