template metaprogramming problem

Question

template <int p>    
bool FComapare (Node *lId, Node* rId)    
{    
    if(lId->getDiff(p) < rId->getDiff(p))
        return true;
    else if(lId->getDiff(p) == rId->getDiff(p))
    {
        if(lId->getLT() < rId->getLT())
            return true;
        else if(lId->getLT() == rId->getLT())
            return (lId->getTFG() < rId->getTFG());
    } 
    return false;
}

vector<set<Node*, bool (*)(Node*,Node*) > > m_F;

for (int i = 0;i < partNum; ++i)
{
    //This doesn`t workbecause of  const problem...
    set<Node *, bool (*)(Node*,Node*) > f(&FComapare<i>);
    m_F.push_back(f);
}

I am getting following error

error C2664: 'std::set<_Kty,_Pr>::set(bool (__cdecl *const &)(Node *,Node *))' : cannot convert parameter 1 from 'bool (__cdecl *)(Node *,Node *)' to 'bool (__cdecl *const &)(Node *,Node *)' 1> with 1> [ 1> _Kty=Node *, 1> _Pr=bool (__cdecl *)(Node *,Node *) 1> ] Reason: cannot convert from 'overloaded-function' to 'bool (__cdecl *const )(Node *,Node *)' 1> None of the functions with this name in scope match the target type

How can I solve the problem and get the same functionality? How do I define correctly

vector<set<Node*, bool (*)(Node*,Node*) > > m_F;

Thanks

"How can I solve the problem and get the same functionality?" - What functionality? You forgot to tell us exactly what functionality you want in the first place. What end goal are you trying to achieve here? — In silico
– In silico, Commented Dec 19, 2010 at 20:03

UncleBens · Accepted Answer · 2010-12-19 20:12:04Z

3

You can't use a variable for the non-type argument.

Instead of a template function, try a function object that stores the value of i.

class FCompare
{
    int p;
public:
    FCompare(int p): p(p) {}
    bool operator()(const Node *lId, const Node* rId) const {...}
};

set<Node *, FCompare > f((FCompare(i)));

answered Dec 19, 2010 at 20:12

UncleBens

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2 Comments

YAKOVM Over a year ago

set<Node *, FCompare > it doesn`t compile

YAKOVM Over a year ago

vector<set<Node*, bool ()(Node,Node*) > > m_F; so how can I define set correctly?

kankan · Accepted Answer · 2010-12-19 20:09:30Z

2

Template parameters should be known at compile time. In your case you are trying to using a local variable to instantiate a template function that is wrong.

I suppose the best solution is don't use a template, just create a class with operator() that will do the same as FComapare() and store the p as a class member.

answered Dec 19, 2010 at 20:09

kankan

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Comments

sepp2k · Accepted Answer · 2010-12-19 20:09:31Z

1

Template arguments need to be known at compile time. You can't use runtime values as template arguments.

Since there is no reason that p needs to be a template parameter in this case, this isn't a problem though. You can just put the logic of FCompare into the operator() of a class, which has p as a member variable and then pass an instance of that class as the argument to set's constructor.

answered Dec 19, 2010 at 20:09

sepp2k

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1 Comment

YAKOVM Over a year ago

How can I define m_F in this case?

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