using BOOST_FOREACH with std::map

The problem is with the first member of the pair, which should be const. Try this:

typedef std::map<int, int> map_t;
map_t mmap;  
BOOST_FOREACH( map_t::value_type &i, mmap )
    i.second++;

This is an old thread, but there is a more convenient solution.

boost has the notion of 'range adapters' that perform a transformation on iterator ranges. There are specific range adapters for this exact use case (iterating over map keys or values): boost::adaptors::map_values and boost::adaptors::map_keys.

So you could iterate over map values like this:

BOOST_FOREACH(int& size, mmap | boost::adaptors::map_values)
{ 
    ++size;
}

More information here.

Another option is to use BOOST_FOREACH_PAIR, see my answer here:

BOOST_FOREACH & templates without typedef