Three dimensional arrays of integers in C++

Question

I would like to find out safe ways of implementing three dimensional arrays of integers in C++, using pointer arithmetic / dynamic memory allocation, or, alternatively using

Answer 1

Each pair of square brackets is a dereferencing operation (when applied to a pointer). As an example, the following pairs of lines of code are equivalent:

x = myArray[4];
x = *(myArray+4);

 

x = myArray[2][7];
x = *((*(myArray+2))+7);

To use your suggested syntax you are simply dereferencing the value returned from the first dereference.

int*** myArray = (some allocation method, keep reading);
//
// All in one line:
int   value = myArray[x][y][z];
//
// Separated to multiple steps:
int** deref1 = myArray[x];
int*  deref2 = deref1[y];
int   value = deref2[z];

To go about allocating this array, you simply need to recognise that you don't actually have a three-dimensional array of integers. You have an array of arrays of arrays of integers.

// Start by allocating an array for array of arrays
int*** myArray = new int**[X_MAXIMUM];

// Allocate an array for each element of the first array
for(int x = 0; x < X_MAXIMUM; ++x)
{
    myArray[x] = new int*[Y_MAXIMUM];

    // Allocate an array of integers for each element of this array
    for(int y = 0; y < Y_MAXIMUM; ++y)
    {
        myArray[x][y] = new int[Z_MAXIMUM];

        // Specify an initial value (if desired)
        for(int z = 0; z < Z_MAXIMUM; ++z)
        {
            myArray[x][y][z] = -1;
        }
    }
}

Deallocating this array follows a similar process to allocating it:

for(int x = 0; x < X_MAXIMUM; ++x)
{
    for(int y = 0; y < Y_MAXIMUM; ++y)
    {
        delete[] myArray[x][y];
    }

    delete[] myArray[x];
}

delete[] myArray;