C++ multi dimensional array [duplicate]

Answer 1

Since this is a question about C++:

Do not use C-style arrays or pointers (neither for 1D nor 2D arrays). Use the C++ data types, such as vector:

vector<int> image(W * H); // 1D array

vector<vector<int> > image(W, vector<int>(H)); // “2D” nested array.

This requires the vector standard header.

Answer 2

int** image = new int*[H];
for(int i = 0; i < H; i++)
    image[i] = new int[W];

Answer 3

I use something like

int ** image....

Answer 4

int *image = new int[W][H]; -- is it wrong??

It will NOT compile. You should compile your code first, to know the answer of your question.

I think you want to do this:

//memory allocation
int **image = new int*[W];
for(size_t i = 0 ; i < W ; i++ )
   image[i] = new int[H];

//use it as
 for(size_t i = 0 ; i < W ; i++ )
    for(size_t j = 0 ; j < H ; j++ )
          image[i][j] = some_value;
int value = image[20][30]; //get value at (20,30) assuming 20 < W and 30 < H

//memory deallocation
for(size_t i = 0 ; i < W ; i++ )
   delete [] image[i];
delete [] image;

But then why do all these when you've std::vector? You could use it which will do all these nasty thing itself. Here is how you should be using std::vector:

std::vector<std::vector<int> > image(W, std::vector<int>(H));
for(size_t i = 0 ; i < W ; i++ )
    for(size_t j = 0 ; j < H ; j++ )
          image[i][j] = some_value;
int value = image[20][30]; //get value at (20,30) assuming 20 < W and 30 < H