Question

One nice example of overloading the function call operator () is to allow another form of double-array subscripting popular in some programming languages. Instead of saying chessBoard[ row ][ column ]for an array of objects, overload the function call operator to allow the alternate form chessBoard( row, column ) Create a class DoubleSubscriptedArray that has similar features to class Array in Figs. 11.611.7. At construction time, the class should be able to create an array of any number of rows and any number of columns. The class should supply operator() to perform double-subscripting operations. For example, in a 3-by-5 DoubleSubscriptedArray called a, the user could write a( 1, 3 ) to access the element at row 1 and column 3. Remember that operator() can receive any number of arguments (see class String in Figs. 11.911.10 for an example of operator()). The underlying representation of the double-subscripted array should be a single- subscripted array of integers with rows * columns number of elements. Function operator() should perform the proper pointer arithmetic to access each element of the array. There should be two versions of operator()one that returns int & (so that an element of a DoubleSubscriptedArray can be used as an lvalue) and one that returns const int & (so that an element of a const DoubleSubscriptedArray can be used only as an rvalue). The class should also provide the following operators: ==, !=, =, << (for outputting the array in row and column format) and >> (for inputting the entire array contents).

Short answer

Define a class with a function call operator that uses pointer arithmetic for 2D access and overloads other operators for comprehensive functionality.

Step-by-step solution

Define Class Attributes

Start by defining the attributes of the class `DoubleSubscriptedArray`. These include the number of rows, number of columns, and a pointer to the type int which will act as a single-subscripted array to store the data.

Create Constructor

Write the constructor to initialize the `DoubleSubscriptedArray` object. The constructor takes two arguments, `rows` and `columns`, and dynamically allocates a single-dimensional array of size `rows * columns` to represent our double-subscripted array.

Define Destructor

Implement the destructor to deallocate the memory allocated for the array when a `DoubleSubscriptedArray` object is destroyed. This prevents memory leaks.

Implement the Function Call Operator

Overload the function call operator `operator()` to allow using the syntax `a(row, column)`. Implement two versions: one returning `int&` to modify elements and another returning `const int&` for read-only access. Use pointer arithmetic to access the correct element: return `array[row * columns + column]`.

Implement Assignment and Equality Operators

Overload the assignment operator `operator=`, the equality operator `operator==`, and the inequality operator `operator!=` to enable operations like copying arrays or comparing them for equality. Ensure to handle same-sized arrays for equality checks.

Implement Input and Output Operators

Overload `operator>>` to input values into the array and `operator<<` to display the array. These operators should traverse the single-dimensional array, reading or printing in a row-and-column format.

Write Main Function for Testing

Write a test function to demonstrate the class functionality. Create instances of `DoubleSubscriptedArray`, use the overloaded operators, and verify they work as intended.

Key concepts

DoubleSubscriptedArray

The `DoubleSubscriptedArray` class in C++ is a clever way to represent two-dimensional arrays using operator overloading. This class is constructed to emulate the behavior of traditional arrays with two subscripts (rows and columns). Instead of having **array[row][column]** syntax, it introduces a more intuitive function call style: **array(row, column)**. To achieve this, the class uses a single-dimensional array internally, which helps simplify memory management and element access.

Here's how it works:

• The class constructor takes two parameters: the number of rows and columns.
• It then allocates memory for a one-dimensional array of size **rows * columns**.
• Elements are accessed using the function call operator, managed by performing pointer arithmetic to translate the two-dimensional coordinates into a linear index.

The single subscripted array structure allows efficient memory use and provides good control over the elements, ensuring each function can be called or referenced accurately. This makes `DoubleSubscriptedArray` both practical and powerful in uses where two-dimensional data needs manipulation.

Function Call Operator

In C++, the function call operator **()** can be overloaded to give objects the appearance of a function. For the `DoubleSubscriptedArray`, overloading this operator offers a dynamic and flexible way to reference elements as if they were in a traditional matrix format.

Overloading **operator()** involves:

• Creating two versions of the operator. One that returns references to allow modification, and another that returns a constant reference for read-only access.
• Using pointer arithmetic to grab the element located at the row and column indices. This is performed by calculating the correct index as **row * columns + column**.

This technique gives the class a natural interface for users, making the double-subscripted access pattern familiar and easy to use. Developers often prefer using function call operators when a class represents a collection they want to access like functions, as it provides a syntactically clean and intuitive interface.

Operator Overloading

Operator overloading is a powerful feature in C++ that allows developers to redefine the meaning of operators for user-defined types. In the `DoubleSubscriptedArray` class, several operators are overloaded to provide a robust set of functions.

Key operators included:

• **Assignment (`operator=`):** This allows easy copying of array objects. It should check self-assignment and ensure deep copying of the array data to avoid shared memory issues.
• **Equality (`operator==` and `operator!=`):** These operators facilitate comparison between two arrays. They check whether the dimensions and the actual data stored in each array match.
• **Input (`operator>>`) and Output (`operator<<`):** These are overloaded to make it easier to read from objects or write out the contents. They traverse the array linearly, presenting or inserting data in a logical row-column format.

Overloading these operators serves to enrich the `DoubleSubscriptedArray` class, making it more intuitive and user-friendly in C++ applications. By integrating these capabilities, the class aligns with common C++ idioms, enhancing the natural feel when interacting with array-like entities.