Confused about specialization of greater predicate??

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I have 2 classes: Card, and CardPile.  My CardPile class has as a state a vector<const Card*>, and a method sortPile().  In the header for my CardPile class, I do the following:
struct greater<const Card*>
   bool operator()(const Card* leftCard, const Card* rightCard) const {
       return ( (*leftCard) < (*rightCard) );
};   //(as suggested by ambience...thank you! )

I then include that file in file, where there is a sortPile method that does the following:

void CardPile::sortPile() {
   sort(_cards.begin(), _cards.end(), greater<Card*>());
}  //_cards is my state which is a vector<const Card*>

All this compiles, until I try to compile it with a main function that includes CardPile's header.  It then crashes and gives me the following error:

'greater' is not a template
explicit specialization of nontemplate '{anonymous struct}'
anonymous class type not used to declare any objects

What am I doing wrong??
Thanks again to ambience for the suggestion, and I imagine it will work
when I figure out what I'm doing wrong!
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Maybe you need to include in the same header file the <functional> header?

Besides, I would have done it differently; I dont see the need to use greater<>() in sort<>(), since as a default it uses less<>(), which calls operator<() for Card.

Did you try defining the following:
bool operator<( const Card& left, const Card& right )
{ /.../ };



The reason I need to use that is because I need to sort it in ascending order and I need to de-reference the Card* so that it will use my Card::operator >, rather than comparing pointers.  

I wasn't including the <functional> header, so I just tried to, and it gave me a big list of compile errors that I can't even read.  They're all from the <algorithm.h> file, and I'm not sure I could tell you what they mean.  

...any idea's??  I'm sure including <functional> is needed, but that doesn't seem to solve the problem...wait...I have an idea...

...IT WORKED!!....thanks for your help!  The problem(in case you were wondering) is that I can't put greater<const Card*>, the const was screwing things up. So I took it out.
Thanks again!!

Dont give up on const...

define sortPile as const, and it will try to use begin() and end() in their const form.

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