Hello,
I've a 3x3 2D dynamic array allocated as below
int** matrix = new int* [3];
matrix[0] = new int [3*3];
for (int i = 1; i < 3; ++i)
matrix[i] = matrix[i-1] + 3;
How should I deallocate it? Is it correct:
delete [] matrix;
delete [] matrix[0];
Or should I also delete matrix[1], [2]
Greetings,
You'll need one delete for each new, in reverse order of the new's.
The code:
delete [] matrix;
delete [] matrix[0];
is obviously wrong, as you use matrix after you delete it.
delete [] matrix[0];
delete [] matrix;
is correct, but I can't vouch that the code as whole does something sensible.
Note that you should not delete matrix[1] and matrix[2] as they are just copies of matrix[0]. A rule of thumb is that you should have the same number of calls to delete as you have calls to new.
Every element in the matrix array is an int[], in addition to that, matrix itself is an array of int* (int*[]), taking these rules into account you should do
delete [] matrix[i] { i=0,1,2 }
and then do delete [] matrix to delete the matrix itself.
Hope this helps. Thanks
You need to read this: http://www.parashift.com/c++-faq-lite/freestore-mgmt.html#faq-16.16
The array of pointers may be unnecessary. You could just allocate the 1D array of 9 elements and do the math to convert 2D indexes to 1D indexes.
In addition to swapping around the delete[] operations, you should consider what happens when an allocation fails. If the second allocation throws std::bad_alloc, your program leaks the memory from the first allocation. A correctly-written matrix class (as suggested by Fred Larson) would handle memory deallocation for you.