Creating custom class for vector of pairs

I have the following code:

Code:

#include <iostream>
#include <utility>
using namespace std;

template<typename T>
class Vector {
	public:
		Vector(unsigned int length = 10) {
		}
};

template<typename P, typename Q>
class Pair {

};

template<typename P, typename Q>
class VectorOfPairs : public Vector<Pair<P, Q> > {
	public:
		VectorOfPairs(unsigned int length = 10) {
			Vector<Pair<P, Q> >::Vector(length);
		}
};

int main() {
	VectorOfPairs<int, int> v;
	return 0;
}

What I'm trying to do inside the "VectorOfPairs(unsigned int)" constructor is what we would write in Java as "super(length)". But for some reason, it gives me a compilation error:

Code:

test.cpp: In constructor `VectorOfPairs<P, Q>::VectorOfPairs(unsigned int) [with P = int, Q = int]':
test.cpp:26:   instantiated from here
test.cpp:21: error: dependent-name ` Vector<Pair<P, Q> >::Vector' is parsed as a non-type, but instantiation yields a type
test.cpp:21: note: say `typename  Vector<Pair<P, Q> >::Vector' if a type is meant

It seems to treat ` Vector<Pair<P, Q> >::Vector' as a type. But in reality, the type is ` Vector<Pair<P, Q> >', while the '::Vector' part is the constructor.

So my question is: is there anyway to tell the compiler that Vector<Pair<P,Q> > is the type?

You can't call a constructor like:

Code:

template<typename P, typename Q>
class VectorOfPairs : public Vector<Pair<P, Q> > {
	public:
		VectorOfPairs(unsigned int length = 10) {
			Vector<Pair<P, Q> >::Vector(length);
		}
};

Try:

Code:

template<typename P, typename Q>
class VectorOfPairs : public Vector<Pair<P, Q> > {
	public:
		VectorOfPairs(unsigned int length = 10) : Vector(length) {
		}
};

But why don't you just use std::vector< std:air<int, int> > ?

Originally Posted by EVOEx

You can't call a constructor like:
Try:

Code:

template<typename P, typename Q>
class VectorOfPairs : public Vector<Pair<P, Q> > {
	public:
		VectorOfPairs(unsigned int length = 10) : Vector(length) {
		}
};

Actually, that would be "Vector<Pair<P, Q> >(length)" instead of "Vector(length)", apparently, since "Vector(length)" gives me a compilation error.

Either way, thank you. But I'm curious: is there really no way to call the Vector constructor actually inside the VectorOfPairs constructor?

Originally Posted by EVOEx

But why don't you just use std::vector< std:air<int, int> > ?

Because this is an assignment where we're supposed to make our own Vector and Pair classes. Sorry for not mentioning that earlier.

>> is there really no way to call the Vector constructor actually inside the VectorOfPairs constructor?

You can, but it won't initialize the base class. All base classes and member variables are initialized before the start of the constructor for your class. If you want to initialize them to a certain value or call a specific constructor for them, you must do so in the initializer list.

In general, you should prefer to use the initializer list to initialize all member variables. You must use it to explicitly initialize base classes.