将模板添加到类中，该模板正在多集合中使用

Question

The fix for this is probably very simple, but I cannot find the answer. An answer will be rewarded with my thanks and my tears.

Basically the below code works just fine without the template (with the T's as primitives of course) but once I add the template, it says my argument list is missing. I figured this has to do with declaring , but these functions are not using scope resolution, at least not in a way I'm familiar with. How do I get this to work?

template<class T>
class Foo
{
public:
    Foo(T s, int i) : Data(s), pri(i) {}

    //Overload the relational operator so that the priority is compared.
    bool operator < (const Foo<T>& n) const { return n.pri < pri; }
    T getData() { return Data; }
    int getId() { return pri; }

private:
    T Data;
    int pri;
};

This is main

int main(void)
{
    set<Foo> s; //These should actually be multiset, but was trying to get it to
    s.insert(Foo("C++", 9)); //work as a set before jumping to multiset
    s.insert(Foo("Is ", 7));
    s.insert(Foo("Fun ", 3));

    set<Foo>::iterator p;
    for (p = s.begin(); p != s.end(); p++)
    {
        Foo n = *p;
        cout << "Id: " << n.getId() << "\t Data: " << n.getData() << endl;
    }

    return 0;
}

If you're curious, the program is supposed to take a string(or other type) along with a priority and sort the priority, the program isn't complete, but I'm supposed to use this Class in my program, but I'm tripped up over in converting it into a template.

Answer 1

std::set expect a type .

Before the introduction of the template part, Foo was a type.

Now that is a template class, Foo isn't a type anymore. Foo<int> is a type; Foo<std::string> is a type; not Foo .

So

std::set<Foo<int>> s;

can work,

std::set<Foo> s;

give an error.

Answer 2

When you declare class Foo {}; , Foo is the name of a class. However, when you declare template <class T> class Foo {}; , Foo is the name of a template. A template is not a class: it's a recipe for creating classes. Classes such as Foo<int> or Foo<char> .

It seems you want to store std::string s in your Foo s in the set, which means the code should look like this:

int main(void)
{
    set<Foo<string>> s; //These should actually be multiset, but was trying to get it to
    s.insert(Foo<string>("C++", 9)); //work as a set before jumping to multiset
    s.insert(Foo<string>("Is ", 7));
    s.insert(Foo<string>("Fun ", 3));

    set<Foo<string>>::iterator p;
    for (p = s.begin(); p != s.end(); p++)
    {
        Foo<string> n = *p;
        cout << "Id: " << n.getId() << "\t Data: " << n.getData() << endl;
    }

    return 0;
}