Expand|Select|Wrap|Line Numbers

1. class CScore
2. {
3. public:
4. int L;
5. int C;
6.  
7. CScore(int l, int c)
8. {
9. L = l;
10. C = c;
11. }
12.  
13. bool operator < (const CScore& score) const
14. {
15. // What to do?
16. }
17. };
18.  

1st Question:
I've this object to insert on a multiset and I want it ordered
descendent by L and after that by C. I know I've to override operator
< but my tries aren't working to keep items listed by that order.

2nd Question:
Before insert I want to check if CScore exists on multiset.
(multiset.find(score) != multiset.end()) doesn't seem to work should I
overload == operator ?
They're equal when L and C match.

Waiting answers. Thanks in advanced!

João Correia wrote:

Expand|Select|Wrap|Line Numbers

1. class CScore
2. {
3.     public:
4.         int L;
5.         int C;
6. >
7.         CScore(int l, int c)
8.         {
9.             L = l;
10.             C = c;
11.         }
12. >
13.         bool operator < (const CScore& score) const
14.         {
15.             // What to do?
16.         }
17. };
18.  

>
1st Question:
I've this object to insert on a multiset and I want it ordered
descendent by L and after that by C. I know I've to override operator
< but my tries aren't working to keep items listed by that order.

Show us what you've tried.

>
2nd Question:
Before insert I want to check if CScore exists on multiset.
(multiset.find(score) != multiset.end()) doesn't seem to work should I
overload == operator ?
They're equal when L and C match.

Checking if find() returns end() will work, but you need to have a
working operator<() first. There's no point overloading operator==()
since the map /set family doesn't use this. From a map or set's point
of view, two keys are equal if neither is less than the other. That is,
A equals B if "A < B" and "B < A" both return false.

Mark

João Correia wrote:

Expand|Select|Wrap|Line Numbers

1. class CScore
2. {
3.     public:
4.         int L;
5.         int C;
6. >
7.         CScore(int l, int c)
8.         {
9.             L = l;
10.             C = c;
11.         }
12. >
13.         bool operator < (const CScore& score) const
14.         {
15.             // What to do?
16.         }
17. };
18.  

>
1st Question:
I've this object to insert on a multiset and I want it ordered
descendent by L and after that by C. I know I've to override operator
< but my tries aren't working to keep items listed by that order.
>
2nd Question:
Before insert I want to check if CScore exists on multiset.
(multiset.find(score) != multiset.end()) doesn't seem to work should I
overload == operator ?
They're equal when L and C match.
>
Waiting answers. Thanks in advanced!
>

This will help you understand how to use multiset
in your context.

HTH

-------------------------------------------------------
#include <iostream>
#include <utility>
#include <set>

using namespace std;

class CScore
{
public:
int L;
int C;

CScore(int l, int c)
{
L = l;
C = c;
}

// the ordering should be a functor not an operator<
// bool operator < (const CScore& score) const
// {
// // What to do?
// }

class StrictWeakOrdering :
public std::binary_function<CScore, CScore, bool>

{
public:
result_type operator()( first_argument_type const & a,
second_argument_type const & b )
{
if( a.L < b.L )
{
return true;
}
else if( a.L == b.L )
{
if( a.C < b.C )
{
return true;
}
}
return false;
}
};

};


int
main()
{
// note you need to explicitly pass in the ordering here
typedef std::multiset<CScore,CScore::StrictWeakOrderingmyM ultiSet;
myMultiSet set;
set.insert( CScore( 1, 1 ) );
set.insert( CScore( 1, 1 ) );
set.insert( CScore( 1, 2 ) );
set.insert( CScore( 2, 1 ) );

if( set.find( CScore(1,1) ) == set.end() )
{
cerr << "(1,1) not in set" << endl;
}
else
{
cerr << "(1,1) in set" << endl;
}

if( set.find( CScore(2,2) ) == set.end() )
{
cerr << "(2,2) not in set" << endl;
}
else
{
cerr << "(2,2) in set" << endl;
}
}
---------------------------------------------
This code prints:
(1,1) in set
(2,2) not in set