hello,every one

now i have a struct like this

struct a {

a(const std::string &m1_, const std::string &m2_, boost::int16_t m3_)

: m1(m1_),m2(m2_), m3(m3_) {}

std::string m1;

std::string m2;

boost::int16_t m3;

};

typedef boost::multi_index::multi_index_container <

boost::multi_index::indexed_by<

boost::multi_index::hashed_unique<

BOOST_MULTI_INDEX_MEMBER(a, std::string, m1)

boost::multi_index::ordered_non_unique<

BOOST_MULTI_INDEX_MEMBER(a, std::string, m2)

boost::multi_index::ordered_non_unique <

BOOST_MULTI_INDEX_MEMBER(a, boost::uint16_t, m3)

> my_data;

i want to list all unique keys of m2 and m3 after the container has been filled with a lot of records, is there a example ?

my_data data;

data.insert(a("a1","k1", 1));

data.insert(a("a2","k1", 2));

data.insert(a("a3","k2", 3));

.....

data.insert(a("a10000","k1", 1));

i want to get all data that m2 equal to "k1", when this data has been processed, get all data that m2 equal to "k2" ... but i do not how many unique keys in the container, am i need to store another set to store that when i fill the container?

i need a function to get the keys like the SQL:"select distinct(m2) from data".

thanks a lot!

best regards.

Bill