C++ Overloading : Overloading the [][] operator [duplicate]

Answer 1

There is no special [][] operator; it's operator[] applied to the result of another operator [].

You can give special meaning to [][] construct by having the first operator returning a special temporary object, which also has [] operator.

Answer 2

No, you will have to overload [] to return a value which itself has [] overloaded.

Answer 3

As others have pointed out, there is no [][] operator, it's a [] operator applied to the results of a [] operator. In the most general case, the first [] operator will return a proxy, which implements itself a [] operator. In the simplest case, the “proxy” can be a T*, since in C++, pointers implement the [] operator. A more generic implementation might be along the lines of:

class ElementProxy
{
    Container* myOwner;
    int myRowIndex;
    int myColumnIndex;
public:
    ElementProxy( Container* owner, int rowIndex, int columnIndex )
        : myOwner( owner )
        , myRowIndex( rowIndex )
        , myColumnIndex( columnIndex )
    {
    }

    operator Type() const  //  lvalue to rvalue conversion
    {
        return myOwner->get( myRowIndex, myColumnIndex );
    }

    void operator=( Type const& rhs ) const
    {
        myOwner->set( myRowIndex, myColumnIndex, rhs );
    }
};

class RowProxy
{
public:
    RowProxy( Container* owner, int rowIndex )
        : myOwner( owner )
        , myRowIndex( rowIndex )
    {
    }
    ElementProxy operator[]( int columnIndex ) const
    {
        return ElementProxy( myOwner, myRowIndex, columnIndex );
    }
};

This isn't perfect; if you are dealing with class types, it's impossible to support something line container[i][j].x, for example; we can't overload operator.. If you need to support this, about the best you can do is overload operator-> on the ElementProxy, and require client code to use -> instead of ., even though it's not really a pointer, smart or otherwise.

Answer 4

There are two operators. To do what you want you must overload operator[] which returns vector of objects.

Answer 5

The subscript operator in c++ is []. when you use a syntax like this "object[][]" you are calling the operator [] to scubscript the first object and then the second operator [] over the object selected by the first.

Substancially you can't overload the operator "[][]" because this operator does not exist. You should overload the subscript operator on the container object and then overload it also in the inner object.