Thread: Templates and Templates objects

Code:

#include <iostream>

using namespace std;

template <class T>
class Array{
    private:
        T* array;
        int size;
    
    public:
        Array();
        Array(int _size);
        Array (Array& rhs);
        ~Array();
        
        T& operator [] (int offset);
};

template <class T>
Array<T>::Array():size(0), array(NULL) {};

template <class T>
Array<T>::Array(int _size): size(_size){
    array=new T[size];
}

template <class T>
Array<T>::Array (Array& rhs){
    size=rhs.size;
    array=new T[size];
    
    for (int i=0;i<size;i++){
        array[i]=rhs[i];    
    }
}

template <class T>
Array <T>::~Array(){
    delete[] array;
} 

template <class T>
T& Array<T>::operator [] (int offset){
//     T t=array[offset];
//     return t;
    return array[offset];
}

class Cat{
    public:
        void meaw (void){
            cout<<"Mieaaw\n";
        }
        
        void present (void){
            cout<<"furrColor: "<<furrColor<<" age: "<<age<<"\n";
        }
        
        string furrColor;
        int age;
        Cat (): furrColor("Black"), age(1){};
};


int main (void){
    
    Array<Cat> array(20)/*[20]*/ ;
    
    for (int i=0;i<20;i++){
        array[i].present();
    }
    
    return 0;
}

First, this

Code:

$ g++ bar.cpp
bar.cpp: In member function ‘T& Array<T>::operator[](int) [with T = Cat]’:
bar.cpp:70:16:   instantiated from here
bar.cpp:45:7: warning: reference to local variable ‘t’ returned [enabled by default]

Note that I return a reference to the actual object, not a reference to a local variable copy of the object.

> Array<Cat> array(20)/*[20]*/ ;
See how this creates an array with 20 elements (the array is inside the Array class).

You can have array[20], but it's a completely different animal, and would need array[x][y] to subscript it!

Line 67 is declaring an array of 20 objects of type Array<cat>. It is not creating an Array<Cat> for which the _size member is equal to 20. Your code is treating it as if it does, hence the compiler complaint. Despite similarity, there is no relationship between "array" (as per meaning of that term in the C or C++ standards) and "Array" (the name of your templated class).


Also, get out of the habit of having member, argument, or variable names prefixed by an underscore. The standard reserves such identifiers for use (in a number of circumstances) by the implementation.

Your copy constructor should take its argument by const reference.
You should also create an assignment operator and make a const version of the index operator.
You are also aware that this essentially duplicates std::vector, yes?

Originally Posted by Dave11

2) this exercise is for studying only. I do aware it's a (bad) replica of <vector> .. thanks

Okay, that's fine. Just checking.