C++ Templates - Specifying a container type and that containers element type that it holds

Question

I want to be able to create a function where I specify a parameter to have both a templated container and a templated element type for that container. Is this possible? I get "error C2988: unrecongnizable template declaration/definition" among others. Here is the function in question.

template<class Iter, class Elem>
 void readIntoP(Iter<Elem> aCont){
ifstream ifss("data.dat");
string aString;
int counter = 0;
item tempItem;
while(ifss >> aString){
    istringstream iss(aString);
    if(counter == 0){
        tempItem.name = aString;
    }else if(counter == 1){
        int aNum = 0;
        iss >> aNum;
        tempItem.iid = aNum;
    }else{
        double aNum = 0;
        iss >> aNum;
        tempItem.value = aNum;
        aCont.push_back(tempItem);
        counter = -1;
    }
    ++counter;
   }
 }

Answer 1

You would need to use a template template parameter, e.g.,

template <template <class> class Iter, class Elem>
void readIntoP(Iter<Elem> aCont) { /* ... */ }

Note, however, that the standard library containers take multiple template parameters (vector, for example, takes two: one for the value type to be stored and one for the allocator to use).

You might instead use a single template parameter for the instantiated container type and then use its value_type typedef:

template <typename ContainerT>
void readIntoP(ContainerT aCont)
{
    typedef typename ContainerT::value_type ElementT;
    // use ContainerT and ElementT
}