Allocating matrices

I forgot how to allocate dynamic matrices! How can I do it??

Code:

---

  int **matrix;
  matrix = new ...
  for(int i...)
      for(int j...)
        matrix[i][j]=...

---

But the only thing I see is a matrix beeing allocated within a for. Can't I allocate all the memory that I want at once?

>Can't I allocate all the memory that I want at once?
Yes, but if you want to use array-like indexing you'll have to work a bit harder than that. You can find a number of different methods for allocating matrices through a board search even though the most common one uses loops to handle multiple dimensions.

Ok thanks than :)

Hi there! I made what I was told to do, but now I get Segmentation fault. Does anyone know why?

Code:

---

        int **edges;
        *edges = new int[num_nodes];
        assert(*edges);
       
        for(int i=0;i<num_nodes;i++)
        {
                edges[i] = new int[num_nodes];
        }

        cout << "Edges generated" << endl;

---

The cout never occur!!!

>*edges = new int[num_nodes];
*edges doesn't point to anything. Never dereference until you have something to reference. Try this instead:

Code:

---

edges = new int*[num_nodes];
assert(edges != 0);

---

Also, the current standard requires new to throw an exception if it fails except when tagged with (nothrow). If you have a compiler that conforms to this then the assert is useless.

THANKS SO MUCH!! IT WORKED(of course!)!!!
Now, just one more question: Do I still need the for to allocate the matrix? I've never see this way of allocating before!!!!!!

>Do I still need the for to allocate the matrix?
Yes. You're using a pointer to a pointer here so you'll need to allocate first an array of pointers, then allocate memory to each of the pointers in the array. Then you'll have a matrix.

Understood!!! Thanks again!!!