Question

I am trying to return an array Data Member from one smaller 2D Array Object, and trying to insert the array into a larger 2D array object. But when attempting this, I came into two problems.

First problem is that I want to return the name of the 2D array, but I do not know how to properly syntax to return 2D Array name.

This is what my 2D Array data member looks like

 private: int pieceArray[4][4]; // 2D Smaller Array 

and I want to return this array into a function, but this one causes a compiler error:

 int Piece::returnPiece() {     return pieceArray; //not vaild     // return the 2D array name } 

I tired using this return type and it worked:

 int Piece::returnPiece() {     return pieceArray[4][4]; } 

But I am unsure if this is what I want, as I want to return the array and all of it’s content.

The other problem is the InsertArray() function, where I would put the returnPiece() function in the InsertArray()’s argument.

The problem with the InsertArray() is the argument, heres the code for it:

 void Grid::InsertArray( int arr[4][4] ) //Compiler accepts, but does not work {     for(int i = 0; i < x_ROWS ; ++i)     {          for (int j = 0; j < y_COLUMNS ; ++j)          {              squares[i][j] = arr[i][j];          }     } } 

The problem with this is that it does not accept my returnPiece(), and if i remove the ‘[4][4]’, my compiler does not accept.

Mostly all these are syntax errors, but how do I solve these problems?

1. Returning the whole pieceArray in returnPiece()
2. The correct syntax for the argument in InsertArray()
3. The argument of InsertArray() accepting the returnPiece()

These 3 are the major problems that I need help with, and had the same problem when I attempt to use the pointer pointer method. Does anyone know how to solve these 3 problems?

Answer 1

When passing your array around, you have to decide whether or not you want to make a copy of the array, or if you just want to return a pointer to the array. For returning arrays, you can’t (easily) return a copy – you can only return a pointer (or reference in C++). For example:

// Piece::returnPiece is a function taking no arguments and returning a pointer to a // 4x4 array of integers int (*Piece::returnPiece(void))[4][4] {     // return pointer to the array     return &pieceArray; } 

To use it, call it like so:

int (*arrayPtr)[4][4] = myPiece->returnPiece(); int cell = (*arrayPtr)[i][j];  // cell now stores the contents of the (i,j)th element 

Note the similarity between the type declaration and using it – the parentheses, dereferencing operator *, and brackets are in the same places.

Your declaration for Grid::InsertArray is correct – it takes one argument, which is a 4×4 array of integers. This is call-by-value: whenever you call it, you make a copy of your 4×4 array, so any modification you make are not reflected in the array passed in. If you instead wanted to use call-by-reference, you could pass a pointer to an array instead:

// InsertArray takes one argument which is a pointer to a 4x4 array of integers void Grid::InsertArray(int (*arr)[4][4]) {      for(int i = 0; i < x_ROWS; i++)      {          for(int j = 0; j < y_COLUMNS ; j++)              squares[i][j] = (*arr)[i][j];      } } 

These type declarations with pointers to multidimensional arrays can get really confusing fast. I recommend making a typedef for it like so:

// Declare IntArray4x4Ptr to be a pointer to a 4x4 array of ints typedef int (*IntArray4x4Ptr)[4][4]; 

Then you can declare your functions much more readable:

IntArray4x4Ptr Piece::returnPiece(void) { ... } void Grid::InsertArray(IntArray4x4Ptr arr) { ... } 

You can also use the cdecl program to help decipher complicated C/C++ types.