Array of objects, difference between Java and C++

Question

I am new to C++ and I am porting over a Java project to C++.

Consider the following Java code, where Piece is a class representing a chess piece:

Piece[][] myPieces = new Piece[8][8];

It creates an array where all the entries are null.

How can I achieve the same thing in C++? I tried:

Piece* myPieces = new Piece[8][8];

But this will create an array with all the entries initialized with the default constructor.

Thanks

Edit: I want the C++ code to be efficient/elegant and I do not care nor wnant to copy paste from Java to C++. I am happy to heavily modify the code structure if needed.

Edit 2: The code is for chess programm, the size of the array will never change and performance is critical.

Answer 1

The simplest way to declare an 8x8 array of optional objects in C++ is like so:

boost::optional<Piece> myPieces[8][8];

The boost::optional type represents an optional object (like your nullable references in Java) that doesn't have all the pitfalls of using pointer types. It should be available as part of the standard library in the next few years.

You may prefer to use the std::array type, which is an encapsulation of fixed-size arrays that allows them to be treated as first-class citizens and also provides a nicer interface:

std::array<std::array<boost::optional<Piece>, 8>, 8> myPieces;

If you want to be able to resize your arrays at run-time, consider std::vector instead.

Answer 2

As you want it performant, and right for C++ instead of a dumb translation, how about this:

Use a size-1 POD-type for piece.
Add all the convenience-methods you might want to it:

struct Piece {
    unsigned char value;
    constexpr Piece() : value() {}
    constexpr operator bool() const {return !value;}
    constexpr bool empty() const {return *this;};
    constexpr bool black() const {return value&0x80;}
    constexpr bool white() const {return value && !black();}
    constexpr unsigned piece() const {return value & 0x7f;}
};

Now that would be an equivalent raw array:

Piece board[8][8];

Or use std::array:

#include <array>
std::array<std::array<Piece, 8>, 8> board;