CODEWITHSUNDEEP
c++templates
JosiP
JosiP

Reputation: 3079

using methods within templates in c++

I'm trying to get basic view of templates and i'm very confused. I have 3 classes, each based on template:

#include <map>

using namespace std;

typedef void (*cb1)(int a, int b);
typedef void (*cb2)(int a, int b, int c);

template <class H>
class CHandle{
    H m_id;
};

template <typename H>
class HndFactory {
public:
    CHandle<H>* createHandle() {
        return new CHandle<H>();
    }
};

template <typename H>
CHandle<H> *createHandle(){
    CHandle<H> *h = new CHandle<H>();
    h->m_id = 100;
    return h;
}

template <class S>
class CSubscriber{
    S m_proc;
};

template <class H, class S>
class CEvent{
    H m_handle;
    S m_subscriber;
    std::map<CHandle<H>, CSubscriber<S> > m_map;
public:
    void subscribe(CHandle<H> *h);
    void unsubscribe(CHandle<H> *h);
};
template <class H, class S>
void CEvent<H, S>::subscribe(CHandle<H> *h){

}
int main(void){
    HndFactory<int> f;
    CSubscriber<cb1> s;
    CHandle<int> *h = f.createHandle();
    CEvent<CHandle<int>, CSubscriber<cb1> > myevent;
    myevent.subscribe(h);
    return 0;
}

when i'm trying to run method "myevent.subscribe" i got this compiler error:

CGlue.cpp: In function âint main()â:
CGlue.cpp:64: error: no matching function for call to âCEvent<CHandle<int>, CSubscriber<void (*)(int, int)> >::subscribe(CHandle<int>*&)â
CGlue.cpp:54: note: candidates are: void CEvent<H, S>::subscribe(CHandle<H>*) [with H = CHandle<int>, S = CSubscriber<void (*)(int, int)>]

How shall i call this method in a proper way ? I tought that when i create object 'h' it has already defined type ?

best regards J.

Upvotes: 0

Views: 82

Answers (3)

user93353
user93353

Reputation: 14039

You either need to change your class members to

std::map<H, S> m_map;

void subscribe(H *h);
void unsubscribe(CHandle<H> *h);

or

Your CEvent object should be declared as

CEvent<int, cb1> myevent;

You have to make one of these 2 changes.

Your current code does the template thing twice. With

template <class H, class S>
class CEvent{

and 

CEvent<CHandle<int>, CSubscriber<cb1> > myevent;

what you have is

H == CHandle<int> & S = CSubscribe<cb1>

So

void subscribe(CHandle<H> *h);

becomes 

void subscribe(<CHandle<CHandle<H> > * h);

once the template is instantiated.

Upvotes: 0

Mark B
Mark B

Reputation: 96241

The error message actually tells you what's wrong here with a little digging into its details:

candidates are: void CEvent<H, S>::subscribe(CHandle<H>*) [with H = CHandle<int>

From this we see that the candidate method is listed, with template type and the type being deduced for H. When you substitute H with the type in question you get a candidate of:

void CEvent<H, S>::subscribe(CHandle<CHandle<int> >*) which now hopefully clearly doesn't match the CHandle<int> being passed in.

Instead, I think you want to use CEvent<int, cb1> myevent; as your event object. Note that you may wish to use a typedef for the various handle and subscriber types within the CEvent class as it may make future maintenance easier.

Upvotes: 0

ecatmur
ecatmur

Reputation: 157354

CEvent<CHandle<int>, CSubscriber<cb1> > myevent;

should be

CEvent<int, cb1> myevent;

Upvotes: 2

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