stl container with 2 keys

[haoshi]

Hello all,

I need a container which can handle 2 keys. Actually I need the sequence is sorted by primary key(a date time) and then second key(a businessId). Can any body help me on this?

Thanks in advance.

[Philip Nicoletti]

You can use pretty much any container you want, you just need
to specify a sorting function ob ject that does what you want.
Here is a sample using vector and set ...


#include <vector>
#include <algorithm>
#include <iostream>
#include <set>

struct S
{
S() {}
S(int d , int i) : date(d) , id(i) {}
int date;
int id;
};

struct SortByDateID
{
bool operator () (const S & lhs , const S & rhs) const
{
// sort by primary key first (date)

if ( lhs.date < rhs.date ) return true;
if ( lhs.date > rhs.date ) return false;

// here the dates are equal , sort by secondary key (id)

return lhs.id < rhs.id;
}
};

using namespace std;

int main()
{
vector<S> v;

v.push_back( S(1,1) );
v.push_back( S(2,3) );
v.push_back( S(5,1) );
v.push_back( S(2,1) );
v.push_back( S(2,8) );

sort( v.begin() , v.end() , SortByDateID() );

//print sorted vector

for (int i=0; i<v.size(); ++i)
{
cout << v[i].date << " : " << v[i].id << "\n";
}

cout << "\n\n\n";

set<S,SortByDateID> s;

s.insert( S(1,1) );
s.insert( S(2,3) );
s.insert( S(5,1) );
s.insert( S(2,1) );
s.insert( S(2,8) );

set<S,SortByDateID>::iterator it = s.begin();

while (it != s.end())
{
cout << it->date << " : " << it->id << "\n";
++it;
}

return 0;
}

[haoshi]

Thanks Philip.
Let me extend my requirement. I need an automatic sortable container that can sort by the primary key; I need another mechanism to sort the elements by second key. I need these can be done automatically when I insert an element into the container.
What I am trying is to do is using a multimap to control a sequence of pointer pair. (*it)->first is a pointer to a structure that contains a date and an ID. I can provide a Less<key> function to the container like this:
class MyLess : public binary_function<CKeyStru *, CMyValue *, bool>
{
public:
bool operator()(const CKeyStru * p1, const CKeyStru * p2) const
{
return (_tcscmp(p1->m_bstrId, p2->m_bstrId) < 0);
}
};

Now the elements are sorted by ID in the container. I need it can sorted by second key which is date time. I know that multiset can't do this but I just use this as an example. During the retrieving I can use a loop but I don't want to use a loop.

Any idea is apprecated.