how to implement c++ table lookup?

[HighCommander4]

[][] should word automatically with a map< int, map<int,int> >.....

Although, there is one thing to be careful of. Using [] on a map *will* add that key to the map if it isn't there already (with a default-constructed value, in this case 0).

If you want to be able to test whether or not a pair is in the map yet, you'll have to use find() instead.

Right. I was too lazy to write the error-checking part of the operator[]'s, but looking at it again I now see that it wasn't clear why I had the proxy class. Let me try again:

#include <map>
using namespace std;

class Table
{
    typedef map<int, map<int, int> > TableMap;
    TableMap m_table;

    class proxy
    {
        const map<int, int>& m_map;
        
    public:
        proxy(const map<int, int>& m) : m_map(m) {}

        int operator[](int x) const
        {
            map<int, int>::const_iterator iter = m_map.find(x);
            if (iter == m_map.end())
                // throw exception or something
            else
                return iter->second;
        }
    };        
public:
    Table()
    {
        // initialize table
    }

    proxy operator[](int x) const
    {
        map<int, map<int, int> >::const_iterator iter = m_table.find(x);
        if (iter == m_table.end())
            // throw exception or something
        else
            return proxy(iter->second);
    }
};

If I try some random x and y where table[x][y] doesn't exist, it will make one? And then return 0 ?

Yup. That's the point of the proxy class. Otherwise you could just do this:

#include <map>
using namespace std;

class Table
{
    typedef map<int, map<int, int> > TableMap;
    TableMap m_table;

public:
    Table()
    {
        // initialize table
    }

    const map<int, int>& operator[](int x) const
    {
        return m_table[x];
    }
};

(or even just a conversion operator to const map<int, map<int, int> >&).